No description available.

An understanding of the distribution of the Bracken fern (Pteridium aquilinum (L.) Kuhn) is critical for providing an appropriate management strategy. In this regard, remote sensing can play a critical role in mapping and modelling such distribution. In this study, an integrated approach using the random forest, maximum likelihood and vegetation indices was developed and tested to determine the capability of WorldView-2 multispectral eight band image in characterising the Bracken fern. Results based on the WorldView-2 were further compared to SPOT-5 multispectral (MS) image findings. The WorldView-2 (WV-2) image was spectrally resized to four traditional bands (blue, 450-510nm; green, 510-580 nm; red, 630-690 nm and NIR1, 770-895 nm) and four additional bands (coastal blue, 400-450 nm; yellow, 585-625 nm; red-edge, 705-745 nm and NIR2, 860-1040 nm) to evaluate the practicality of the spectral resolution in mapping the Bracken fern. The results from this analysis showed that the spectrally resized additional bands were more successful in general land cover mapping and characterising the Bracken fern. The result’s overall accuracy was 79.14% while the user’s and producer’s accuracies were 97.62% and 91.11% respectively. The second part of the study sought to improve the classification accuracy by applying a robust machine learning algorithm, the random forest. Since the random forest does not automatically choose the optimal bands, the backward variable elimination technique was employed to identify the optimum wavelengths in WV-2 for the identification of the Bracken fern. Respective out-of-bag (OOB) errors of 13.1% and 9.17% were achieved when the WV-2’s eight bands and optimally selected bands (n= 5) were used. These bands lie in the green (510-580nm), near-infrared1 (770-895nm), red-edge (705-745nm), near-infrared2 (860-1040nm) and the coastal blue (400-450nm) regions of the electromagnetic spectrum. These findings confirm the importance of the additional bands in vegetation analyses. The vegetation indices computed from these regions of the spectrum were superior to those in the visible region. The classification accuracy using WV-2 bands was superior to that from the commonly used SPOT 5 image. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2014.

A infestação de pastagens por populações de Pteridium arachnoideum é um problema que afeta a pecuária, em diversas partes do mundo. Os efeitos deletérios da infestação pela planta sobre a bovinocultura são manifestados na forma de mortalidades e de redução das áreas de pastagens, assim como de perdas produtivas. Devido à importância dessas perdas na produção de bovinos, foi proposto o acompanhamento de uma propriedade do Rio Grande do Sul com problemas decorrentes da infestação pela planta em sua casuística e métodos de controle empregados. Adicionalmente, realizou-se teste da viabilidade de ovinos como ferramenta de controle biológico. Dos casos de intoxicação naturais acompanhados na propriedade, observou-se a ocorrência de quadro agudo de diátese hemorrágica e de quadro crônico de carcinomas do trato digestório superior. Observou-se que quando expostos a fatores predisponentes, como a introdução em áreas recentemente roçadas, os bovinos podem consumir altas doses da planta e assim desenvolver a enfermidade aguda em forma de surtos. Em diversos bovinos jovens com quadro de diátese hemorrágica, além das hemorragias disseminadas e infartos múltiplos, observou-se acentuado edema laríngeo, que cursava clinicamente com dispneia e estertores respiratórios característicos. Os carcinomas do trato digestório superior, apesar de menos frequentes, causaram expressivas perdas devido a mortalidades anuais de matrizes. A tentativa de controle pelo pastejo por ovinos não foi eficiente, devido ao consumo pouco expressivo na lotação praticada. Mortalidade de ovinos, no entanto, decorrente do consumo da planta não foi registrada. O método de combate à planta aplicado na propriedade combinava ou associava a roçagem em áreas densamente povoadas com o uso de herbicidas, nomeadamente metilsulfuron-metil e picloram, em todos os piquetes. A redução da cobertura da P. arachnoideum foi variada em diferentes piquetes; entretanto, possibilitou a recuperação de algumas áreas de pastejo. / The infestation of pastured areas by Pteridium arachnoideum populations has been a considerable and global problem to the livestock production. The deleterious effects of the plant infestation on cattle are manifested as animal mortality and pasture coverage reduction. Given the importance of P. arachnoideum in cattle production, it has been proposed to monitor a beef cattle farm in Rio Grande do Sul, to assess some of the losses associated with the plant consumption apart of the methods employed for controlling the plant. In addition, the viability of sheep’s grazing as a biological control tool was tested. Cases of natural poisoning observed in the farm included the acute form, known as hemorrhagic diathesis as well as the chronic form, consisting in digestive carcinomas. When cattle were exposed to any predisposing factor, such as being moved to newly mowed areas, it was noted that the amount of plant consumed can readily lead to an outbreak of acute poisoning. Several cases of hemorrhagic diathesis in young cattle went along with marked laryngeal edema, which was clinically manifested as dyspnea and roaring, in addition to the classic pathological changes of widespread hemorrhages and infarcts. Even though less frequent, carcinomas of the upper digestive tract caused significant losses, due to annual mortality of mature cows. The attempt through grazing by sheep wasn’t efficient to control P. aquilinum, due to the low consumption of the plant seen in the actual stocking. However, sheep mortality, by P. arachnoideum consumption was not recorded. The plant control method applied at the farm combined mowing of densely populated areas with herbicide applications, namely metilsulfuron-methyl and picloram, in all paddocks. The reduction of P. arachnoideum coverage was varied in different paddocks; however, allowed the recovery of some grazing areas.

A infestação de pastagens por populações de Pteridium arachnoideum é um problema que afeta a pecuária, em diversas partes do mundo. Os efeitos deletérios da infestação pela planta sobre a bovinocultura são manifestados na forma de mortalidades e de redução das áreas de pastagens, assim como de perdas produtivas. Devido à importância dessas perdas na produção de bovinos, foi proposto o acompanhamento de uma propriedade do Rio Grande do Sul com problemas decorrentes da infestação pela planta em sua casuística e métodos de controle empregados. Adicionalmente, realizou-se teste da viabilidade de ovinos como ferramenta de controle biológico. Dos casos de intoxicação naturais acompanhados na propriedade, observou-se a ocorrência de quadro agudo de diátese hemorrágica e de quadro crônico de carcinomas do trato digestório superior. Observou-se que quando expostos a fatores predisponentes, como a introdução em áreas recentemente roçadas, os bovinos podem consumir altas doses da planta e assim desenvolver a enfermidade aguda em forma de surtos. Em diversos bovinos jovens com quadro de diátese hemorrágica, além das hemorragias disseminadas e infartos múltiplos, observou-se acentuado edema laríngeo, que cursava clinicamente com dispneia e estertores respiratórios característicos. Os carcinomas do trato digestório superior, apesar de menos frequentes, causaram expressivas perdas devido a mortalidades anuais de matrizes. A tentativa de controle pelo pastejo por ovinos não foi eficiente, devido ao consumo pouco expressivo na lotação praticada. Mortalidade de ovinos, no entanto, decorrente do consumo da planta não foi registrada. O método de combate à planta aplicado na propriedade combinava ou associava a roçagem em áreas densamente povoadas com o uso de herbicidas, nomeadamente metilsulfuron-metil e picloram, em todos os piquetes. A redução da cobertura da P. arachnoideum foi variada em diferentes piquetes; entretanto, possibilitou a recuperação de algumas áreas de pastejo. / The infestation of pastured areas by Pteridium arachnoideum populations has been a considerable and global problem to the livestock production. The deleterious effects of the plant infestation on cattle are manifested as animal mortality and pasture coverage reduction. Given the importance of P. arachnoideum in cattle production, it has been proposed to monitor a beef cattle farm in Rio Grande do Sul, to assess some of the losses associated with the plant consumption apart of the methods employed for controlling the plant. In addition, the viability of sheep’s grazing as a biological control tool was tested. Cases of natural poisoning observed in the farm included the acute form, known as hemorrhagic diathesis as well as the chronic form, consisting in digestive carcinomas. When cattle were exposed to any predisposing factor, such as being moved to newly mowed areas, it was noted that the amount of plant consumed can readily lead to an outbreak of acute poisoning. Several cases of hemorrhagic diathesis in young cattle went along with marked laryngeal edema, which was clinically manifested as dyspnea and roaring, in addition to the classic pathological changes of widespread hemorrhages and infarcts. Even though less frequent, carcinomas of the upper digestive tract caused significant losses, due to annual mortality of mature cows. The attempt through grazing by sheep wasn’t efficient to control P. aquilinum, due to the low consumption of the plant seen in the actual stocking. However, sheep mortality, by P. arachnoideum consumption was not recorded. The plant control method applied at the farm combined mowing of densely populated areas with herbicide applications, namely metilsulfuron-methyl and picloram, in all paddocks. The reduction of P. arachnoideum coverage was varied in different paddocks; however, allowed the recovery of some grazing areas.

Submitted by Daniele Amaral (daniee_ni@hotmail.com) on 2016-10-05T20:11:42Z No. of bitstreams: 1 TeseLJJ.pdf: 3082295 bytes, checksum: 1f3b55b503c9c9ccf53f773842702e2c (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-20T16:22:19Z (GMT) No. of bitstreams: 1 TeseLJJ.pdf: 3082295 bytes, checksum: 1f3b55b503c9c9ccf53f773842702e2c (MD5) / Approved for entry into archive by Marina Freitas (marinapf@ufscar.br) on 2016-10-20T16:22:27Z (GMT) No. of bitstreams: 1 TeseLJJ.pdf: 3082295 bytes, checksum: 1f3b55b503c9c9ccf53f773842702e2c (MD5) / Made available in DSpace on 2016-10-20T16:22:36Z (GMT). No. of bitstreams: 1 TeseLJJ.pdf: 3082295 bytes, checksum: 1f3b55b503c9c9ccf53f773842702e2c (MD5) Previous issue date: 2016-03-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Pteridium plants are ferns (monilopytes) distributed all around the globe. These plants are considered problem species as they invade recently abandoned or burned areas, and areas under anthropogenic impacts. In Brazil, Pteridium arachnoideum (Kaulf.) Maxon. has become an important problem species at the Cerrado (Tropical Savanna) and Atlantic Forest biomes. To understand the mechanisms underlying invasive plants success are one of the greatest challenges of the last decades. Among the interaction that can influence this success, we find allelopathy. However, untill now we have few evidences for this phenomenon on these plants, especially from the isolation and indentification of secondary metabolites with activities related to allelopathy. Therefore, the present work aimed to evaluate the allelopathy role by direct phytotoxicity and abiotic changes in Pteridium arachnoideum (Kaulf.) Maxon. dominance in the areas it invades. To do so, the bioguided phytochemical study of this plant tissues and litter was performed, as well as the evaluation of the phytotoxic activity of phenolic compounds present in its litter and of its isolated and identified secondary metabolite against the early development of sesame, verifying the presence of this compound in the soil, its quantification, and evaluation of its interactions with physical and chemical soil characteristics. The phytochemical study led to the isolation and identification of a majoritarian compound in the plants green fronds and litter, the proanthocianidin selligueian A. This is the first time this compound is described for P. arachnoideum, as well as for the Dennstaediaceae family. Selligueain A showed phytotoxic activity against wheat coleoptiles elongation, with inhibitory activity over 71%, and IC50 of 0.69 mM. The poliphenols enriched fraction extracted from P. arachnoideum litter exert inhibitory activity against the early development of bioindicators species, native and invasive species of the Cerrado biome, specially over the development of these seedlings roots, besides activity against the metaxylem cells of sesame, and against chlorophyll content of sesame and the native weed Setaria parviflora. The allelopathic potential of the main poliphenolic compound of P. arachnoideum, selligueain A, was also evaluated against the early growth of sesame seedlings, promoting root and shoot growth in all the concentrations tested. Sesame seedlings grown in the presence of selligueain A showed smaller metaxylem cells when compared to the control, in the concentrations of 0.3 mM e 1 mM, with 50.82% inhibition in the greatest concentration and IC50 value of 0.98 mM. There was no activity of selligueain A against chlorophyll content of these seedlings. Analyses of extracts of soil collect under a P. arachnoideum patches pointed to the presence of selligueain A as major compound in soil solution, and, therefore, as a putative allelochemical produced by this plant. The concentration observed for this compound in the soil raged between 0.02 and 0.65 mM. According to allelopathic potential results, this concentration rage is sufficient to act over cooccurring plant species, promoting P. arachnoideum dominance. The presence of P. arachnoideum in Cerrado areas alters the chemical conditions of the soil, especially regarding N and Al, when compared to the presence of U. decumbens. Additionally, Al concentration is correlated to litter mass and to selligueain A concentration at the sites sampled. These results corroborates the hypothesis of allelopathy as a dominance mechanism of this plant in the areas where it occurs, with the first report of an allelochemical for a Pteridium species, by direct phytotoxic activity as well as by controlling Al concentration at those areas. / Plantas do gênero Pteridium são samambaias (monilófitas) e estão distribuídas em todo mundo. São consideradas espécies problemas pois invadem áreas recentemente queimadas, abandonadas ou sob impacto antrópico. No Brasil, Pteridium arachnoideum (Kaulf.) Maxon. apresenta-se como uma importante espécie problema do Cerrado e da Mata Atlântica. Compreender os mecanismos que governam o sucesso de plantas com comportamento invasor tem se mostrado um dos maiores desafios das últimas décadas. Dentre as interações que podem influenciar este sucesso está a alelopatia. No entanto, poucas são as evidências apresentadas até então para este fenômeno, especialmente a partir do isolamento e identificação de substâncias do metabolismo secundário destas plantas. Assim, o objetivo deste trabalho foi avaliar o papel da alelopatia por fitotoxicidade direta e alterações abióticas na dominância de P. arachnoideum nas áreas em que ocorre. Para isso, foi realizado estudo fitoquímico biodirigido de diferentes órgãos e serrapilheira desta planta, avaliação da atividade fitotóxica dos polifenóis e do metabólito secundário isolado e identificado sobre o desenvolvimento inicial da espécie bioindicadora gergelim, identificação da presença deste composto no solo, sua quantificação e avaliação de sua interação com características físicoquímicas do solo. O estudo fitoquímico levou ao isolamento de um composto majoritário presente em suas frondes verdes e serrapilheira desta planta, a proantocianidina selligueina A. Esta é a primeira vez que este composto é descrito para P. arachnoideum, assim como para a família Dennstaediaceae. A selligueina A apresentou atividade fitotóxica sobre o alongamento de coleóptilos de trigo, com atividade inibitória acima de 71%, e IC50 de 0,69 mM. A fração enriquecida em polifenóis extraídos da serrapilheira de P. arachnoideum exerceu atividade inibitória sobre o desenvolvimento inicial de espécies bioindicadoras, nativa e invasora do Cerrado, especialmente sobre o desenvolvimento das raízes dessas plântulas, e atividade sobre as células do metaxilema de gergelim, e sobre o conteúdo de clorofila de gergelim e de capim rabo-de-raposa. O potencial alelopático do principal composto polifenólico desta planta, selligueina A, também foi testado sobre o crescimento inicial de gergelim, promovendo inibição do comprimento final do caule e da raiz de plântulas de gergelim em todas as concentrações testadas. Plântulas de gergelim crescidas na presença de selligueina A apresentaram células do metaxilema menores do que o as do controle nas concentrações de 0,3 mM e 1 mM, com inibição de 50,82% na maior concentração e IC50 de 0,98 mM. Não houve atividade de selligueina A sobre o conteúdo de clorofila dessas plântulas. Análises dos extratos de solo coletado sob manchas de P. arachnoideum apontaram a presença de selligueina A como composto majoritário na solução do solo, e, portanto, como aleloquímico produzido por esta planta. As concentrações do composto no solo variaram entre 0,02 e 0,65 mM. De acordo com resultados de potencial alelopático essa faixa de concentração seria suficiente para potencialmente atuar sobre espécies co-ocorrentes, favorecendo a dominância de P. arachnoideum. A presença de P. arachnoideum em áreas de Cerrado altera condições químicas do solo, especialmente com relação à concentração do nutriente N e de Al, quando comparada à presença de braquiária (U. decumbens). Além disso, a concentração de Al se encontra correlacionada à massa de serrapilheira e à concentração de selligueina A nas áreas amostradas. Estes resultados corroboram a hipótese de alelopatia como mecanismo de dominância dessa planta nas áreas em que ocorre, com a primeira descrição de um aleloquímico para uma espécie do gênero Pteridium, que apresenta atividade não apenas por fitotoxicidade direta, mas também por ação indireta, ao controlar a concentração de Al nessas áreas.

A infestação de pastagens por populações de Pteridium arachnoideum é um problema que afeta a pecuária, em diversas partes do mundo. Os efeitos deletérios da infestação pela planta sobre a bovinocultura são manifestados na forma de mortalidades e de redução das áreas de pastagens, assim como de perdas produtivas. Devido à importância dessas perdas na produção de bovinos, foi proposto o acompanhamento de uma propriedade do Rio Grande do Sul com problemas decorrentes da infestação pela planta em sua casuística e métodos de controle empregados. Adicionalmente, realizou-se teste da viabilidade de ovinos como ferramenta de controle biológico. Dos casos de intoxicação naturais acompanhados na propriedade, observou-se a ocorrência de quadro agudo de diátese hemorrágica e de quadro crônico de carcinomas do trato digestório superior. Observou-se que quando expostos a fatores predisponentes, como a introdução em áreas recentemente roçadas, os bovinos podem consumir altas doses da planta e assim desenvolver a enfermidade aguda em forma de surtos. Em diversos bovinos jovens com quadro de diátese hemorrágica, além das hemorragias disseminadas e infartos múltiplos, observou-se acentuado edema laríngeo, que cursava clinicamente com dispneia e estertores respiratórios característicos. Os carcinomas do trato digestório superior, apesar de menos frequentes, causaram expressivas perdas devido a mortalidades anuais de matrizes. A tentativa de controle pelo pastejo por ovinos não foi eficiente, devido ao consumo pouco expressivo na lotação praticada. Mortalidade de ovinos, no entanto, decorrente do consumo da planta não foi registrada. O método de combate à planta aplicado na propriedade combinava ou associava a roçagem em áreas densamente povoadas com o uso de herbicidas, nomeadamente metilsulfuron-metil e picloram, em todos os piquetes. A redução da cobertura da P. arachnoideum foi variada em diferentes piquetes; entretanto, possibilitou a recuperação de algumas áreas de pastejo. / The infestation of pastured areas by Pteridium arachnoideum populations has been a considerable and global problem to the livestock production. The deleterious effects of the plant infestation on cattle are manifested as animal mortality and pasture coverage reduction. Given the importance of P. arachnoideum in cattle production, it has been proposed to monitor a beef cattle farm in Rio Grande do Sul, to assess some of the losses associated with the plant consumption apart of the methods employed for controlling the plant. In addition, the viability of sheep’s grazing as a biological control tool was tested. Cases of natural poisoning observed in the farm included the acute form, known as hemorrhagic diathesis as well as the chronic form, consisting in digestive carcinomas. When cattle were exposed to any predisposing factor, such as being moved to newly mowed areas, it was noted that the amount of plant consumed can readily lead to an outbreak of acute poisoning. Several cases of hemorrhagic diathesis in young cattle went along with marked laryngeal edema, which was clinically manifested as dyspnea and roaring, in addition to the classic pathological changes of widespread hemorrhages and infarcts. Even though less frequent, carcinomas of the upper digestive tract caused significant losses, due to annual mortality of mature cows. The attempt through grazing by sheep wasn’t efficient to control P. aquilinum, due to the low consumption of the plant seen in the actual stocking. However, sheep mortality, by P. arachnoideum consumption was not recorded. The plant control method applied at the farm combined mowing of densely populated areas with herbicide applications, namely metilsulfuron-methyl and picloram, in all paddocks. The reduction of P. arachnoideum coverage was varied in different paddocks; however, allowed the recovery of some grazing areas.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The epidemiology, pathogenesis, clinical and pathological aspects of the spontaneous and experimental poisoning of cattle by bracken fern (Pteridium aquilinum) were studied. Two scientific papers that stemmed from these studies are presented and discussed here. Initially, 6,256 necropsy reports from cattle necropsied during a de 43-year-period (1964-2006) were reviewed. Of those, 15 cases were consistent with acute poisoning caused by the ingestion of P. aquilinum and they occurred in cattle from small farms in the Central region of the State of Rio Grande do Sul, Brazil. In 40% of the farms the disease occurred in small outbreaks affecting several cattle per farm and in 60% only one bovine was affected in each farm. Morbidity and mortality were 17.9% and lethality was virtually 100%. The poisoning was experimentally produced in four calves; it was concluded that exclusively the events of the primary hemostasis due to thrombocytopenia are responsible for the hemorrhages. Blood culture from three affected calves yield the growth of Klebsiella oxytoca, Staphylococcus hyicus and S. aureus, indicating that septicemia, facilitated by neutropenia could have a role in the death of cattle acutely poisoned due to the ingestion of P. aquilinum. / Foram estudados a epidemiologia, a patogênese, os aspectos clínicos e patológicos da intoxicação aguda, espontânea e experimental, por samambaia (Pteridium aquilinum) em bovinos. Dois trabalhos científicos que resultaram desse estudo são aqui apresentados e discutidos. Inicialmente, foram revisados 6.256 laudos de necropsia de bovinos num período de 43 anos (1964-2006). Desses, 15 casos corresponderam a quadros de intoxicação aguda causada pela ingestão de P. aquilinum e os casos ocorreram em bovinos de pequenas propriedades rurais da Região Central do Rio Grande do Sul. Em 40% das propriedades a doença ocorreu em pequenos surtos e em 60% delas apenas um bovino era afetado por propriedade. As taxas médias de morbidade e mortalidade foram de 17,9% e a letalidade foi virtualmente 100%. A intoxicação foi produzida experimentalmente em quatro bovinos e foi demonstrado que apenas eventos da hemostasia primária devidos a trombocitopenia são responsáveis pelas hemorragias. A hemocultura de três dos bovinos intoxicados produziu crescimentos de Klebsiella oxytoca, Staphylococcus hyicus e S. aureus, indicando que a septicemia, facilitada pela neutropenia, pode ter participação na causa da morte de bovinos na intoxicação aguda pela ingestão de P. aquilinum.

In the present thesis, implications of pasture establishment, fertilization and abandonment on soil C and nutrient dynamics were investigated for the mountain rainforest region of southern Ecuador. Over the past decades the natural forest of the study area has been threatened by conversion to cattle pastures. However, the soil fertility of these extensively grazed pastures (active pastures) declines continuously during pasture use. The invasion of bracken fern (Pteridium arachnoideum) leads to pasture abandonment when bracken becomes dominant. In order to reveal the mechanisms behind the deterioration of soil fertility, biotic and abiotic soil properties and their interaction were analyzed along a land‐use gradient (natural forest – active pasture – abandoned pasture). The ecosystem disturbance of the mountain rainforest through pasture use changed the microbial function and structure, and affected soil CO2‐C fluxes. Annually, 2 Mg soil CO2‐C ha‐1 were additionally emitted from the pasture land. This acceleration in soil respiration rates was related to accelerated rates of microbial C mineralization and fine‐root respiration. The high‐quality, N‐rich above‐ and belowground residues of the pasture grass (S. sphacelata, C4‐plant), especially the huge fine‐root biomass, provided a high C and N availability for soil microbes. Compared to the forest, increased soil pH and accelerated base saturation were further factors beneficial for soil microbial growth and metabolism of the upper mineral soil at active pastures. Three times higher amounts of microbial biomass C and a significant shift in the microbial community structure towards a higher relative abundance of Gram(‐)‐ bacteria and fungi were observed. Long‐term pasture use and the invasion of bracken (C3‐plant) diminished beneficial effects for microbes, causing a significant decrease in the C, net, and gross N mineralization rates as well as a two‐third reduction in the microbial biomass. A preferential substrate utilization of grass‐derived C4 by the soil microbes resulted in a rapid decline of the C4‐pool. As a consequence, the less available C3‐pool from bracken and former forest increased its dominance in the SOC‐pool, further decreasing pasture productivity and finally causing pasture abandonment. The lower quality and quantity of above‐ and belowground residues of the bracken (high lignin content, C/N) resulted in resource‐limited conditions that influenced the microbial function to greater extent than their structure. The microbial structure seemed to be sensitive mainly to soil pH along the land‐use gradient. Thus, a disconnection between microbial structure and function was identified. Fertilization experiments were conducted both in the lab and in the field to evaluate the impact of urea and/or rock phosphate amendment on SOM dynamics and on pasture productivity of active pastures. After combined fertilization the pasture yield was most efficiently increased by 2 Mg ha−1 a−1, indicating a NP‐limitation of grass growth. Furthermore, the fodder quality was improved by a higher content of P and Ca in the grass biomass. The microorganisms of the active pasture soil responded with an adaptation of their structure to the increased substrate availability in the short term, but did not change their initial functions in the long term. After urea/ rock phosphate addition a significant increase in the relative fungal abundance was detected, but neither a microbial limitation of energy nor of N or P was observed. However, urea addition accelerated gaseous losses of soil CO2‐C in the short term. In the study area, pronounced alterations in ecosystem functioning due to land‐use changes were detected, especially in soil C and N cycling rates. For a sustainable land‐use in this region it is crucial to prevent pasture degradation and to rehabilitate degraded pastures in order to protect the prevailing mountain rainforest ecosystem. It is of crucial importance for active pasture soils to maintain or even increase resource availability, being one indicator of soil fertility. In this context, the soil organic matter has to be retained in the long‐term to maintain high microbial activity and biomass, and thus pasture productivity. A moderate fertilization with urea and rock phosphate can be a first step to provide continuous nutrient supply for grass growth and to strengthen livestock health through increased fodder quality. However, the risk of further additional emissions of soil CO2‐C due to increased loads of urea fertilizer application has to be kept in mind. Overall, for the establishment of a sustainable land‐use management the control of bracken invasion and an adjusted nutrient management are needed. Further investigations on the reduction of soil nutrient losses and increased nutrient use efficiencies of plants, such as combined planting with legumes or the usage of cultivars with special nutrient acquisition strategies, should be in the focus of future work. / In der vorliegenden Dissertation werden die Auswirkungen der Weideetablierung, ‐düngung sowie des Verlassens von Weiden auf Bodenkohlenstoff‐ und Nährstoffdynamik in einer tropischen Bergregenwaldregion Ecuadors zusammenfassend dargestellt und diskutiert. Der Naturwald des Untersuchungsgebietes ist seit Jahrzehnten durch Brandrodung und die Umwandlung in extensiv genutztes Weideland (aktive Weide) in seinem flächenhaften Bestand bedroht. Als Problem hat sich der Verlust an Fruchtbarkeit der Weideböden während ihrer Bewirtschaftung herausgestellt. Des Weiteren führt die Einwanderung des Tropischen Adlerfarns (Pteridium arachnoideum, C3‐Pflanze) zu einer Reduktion der oberirdischen Grasbiomasse. Nimmt diese Entwicklung überhand, werden die betroffenen Flächen von den Bauern nicht mehr aktiv genutzt, verlassen und neuer Regenwald gerodet. Um mehr über die Mechanismen der Verringerung der Bodenfruchtbarkeit zu erfahren, wurden biotische und abiotische Bodeneigenschaften und deren Interaktion entlang eines Landnutzungsgradienten (Naturwald – aktive Weide – verlassene Weide) untersucht. Die Zerstörung des Bergregenwaldökosystems und die Überführung der gerodeten Flächen zur Weidebewirtschaftung verändert die Funktion und Struktur der Bodenmikroorganismen und beeinflusst den CO2‐C Fluss aus dem Boden. Jährlich werden 2 t CO2‐C ha‐1 zusätzlich vom Weideland emittiert. Diese Erhöhung der Bodenatmungsraten kann mit erhöhten Raten der mikrobiellen C‐Mineralisierung und Feinwurzelatmung in Verbindung gebracht werden. Das Weidegras (S. sphacelata, C4‐Pflanze) liefert C‐ und N‐reiche ober und unterirdische organische Substanz (z.B. durch die Feinwurzelbiomasse) und trägt damit zu einer Erhöhung der C‐ und N‐Verfügbarkeit für die mikroorganismen bei. Darüber hinaus stellen ein höherer pH‐Wert und eine erhöhte Basensättigung im oberen Mineralboden der aktiven Weide günstige Bedingungen für mikrobielles Wachstum und Metabolismus dar. Als Konsequenz sind die Gehalte an mikrobiellem Biomassekohlenstoff um das Dreifache erhöht und die mikrobiellen Gemeinschaftsstrukturen signifikant in Richtung einer höheren relativen Abundanz der Gram(‐)‐Bakterien und Pilze verschoben. Eine längerfristige Weidebewirtschaftung ohne Kompensation von Nährstoffverlusten sowie die Einwanderung des Tropischen Adlerfarnes verschlechterte die Bedingungen für die Mikroorganismen, was zu einem signifikanten Rückgang des SOC, der Netto‐ und Brutto‐N‐Mineralisierungsraten sowie zu einer Halbierung der mikrobiellen Biomasse führt. Eine bevorzugte Substratnutzung von Graskohlenstoff (C4) durch die Mikroorganismen hat einen schnellen Abbau des C4‐Pools zur Folge. Somit dominiert nun der mikrobiell schlechter verfügbare C3‐Pool den Bodenkohlenstoffpool. Dies führt zu einem weiteren Rückgang der Weideproduktivität und schließlich zum Offenlassen der Weide. Die geringere Qualität und Quantität der vom Farn stammenden ober‐ und unterirdischen organischen Substanz (hoher Ligninanteil, weites C/N), führten zu einer Limitierung der Ressourcen für die Mikroorganismen, welche deren Funktionen in größerem Maße beeinflussen als deren Gemeinschaftsstruktur. Im Gegensatz dazu wird entlang des Landnutzungsgradienten die Struktur hauptsächlich durch den pH‐Wert beeinflusst. Daraus folgt, dass Struktur und Funktion der Bodenmikroorganismen voneinander entkoppelt auf Veränderungen reagieren können. Um den Einfluss von Harnstoff‐ und/ oder Rohphosphatdüngung aktiver Weiden auf die Dynamik der organischen Bodensubstanz und auf die Weideproduktivität zu untersuchen, wurden sowohl Labor‐ als auch Feldversuche durchgeführt. Im Feldexperiment wurde gezeigt, dass eine NP‐Limitierung der Grasbiomasseproduktion vorliegt und durch eine geringe NP‐Kombinationsdüngung die oberirdische Phytomasseproduktion um 2 t ha−1 a−1 gesteigert und die Futterqualität durch eine Erhöhung der P‐ und Ca‐ Gehalte verbessert werden kann. Die Mikroorganismen reagierten mit einer Anpassung ihrer Struktur an die kurzzeitig erhöhte Substratverfügbarkeit. Nach Gabe von Harnstoff und/ oder Rohphosphat wurde weder eine N‐ noch eine P‐Limitierung der Bodenmikroorganismen festgestellt, und die mikrobiellen Funktionen wurden langfristig nicht verändert. Dagegen bewirkte die Düngergabe einen erhöhten relativen Anteil der Pilzabundanz. Im Labor sowie im Feld kam es nach Harnstoffdüngung kurzzeitig zu verstärkten gasförmigen Verlusten des Bodenkohlenstoffs. Aufgrund der Landnutzungsänderungen im Untersuchungsgebiet veränderten sich die Ökosystemfunktionen stark, speziell die Boden‐C‐ und Boden‐N‐Umsatzraten. Für eine nachhaltige Landnutzung in der Region, d. h., für den Schutz der noch verbliebenen natürlichen Bergregenwaldflächen, ist es von entscheidender Bedeutung, dass die Weidedegradierung verhindert wird und degradierte Flächen wieder in Nutzung genommen werden. Als entscheidend für die Weideproduktivität hat sich in dieser Studie die Ressourcenverfügbarkeit für Bodenmikroorganismen herausgestellt. Daher ist es sehr wichtig, diese Ressourcenverfügbarkeit in Böden aktiv‐genutzter Weiden zu erhalten oder noch zu erhöhen, denn sie wirkt sich vor allem auf die organische Bodensubstanz und im Wechselspiel damit auf die mikrobielle Biomasse und Aktivität aus. Eine moderate Kombinationsdüngung aus Harnstoff und Rohphosphat ist ein erster Schritt in diese Richtung. Dabei sollte jedoch das Risiko zusätzlicher bodenbürtiger CO2‐C Emissionen in Folge höherer Düngergaben berücksichtigt werden. Für ein nachhaltiges Landnutzungsmanagement sind Maßnahmen gegen die Einwanderung des Adlerfarnes und ein angepasstes Nährstoffmanagement notwendig. Weitere Untersuchungen sollten auf eine Minimierung der Nährstoffverluste und eine erhöhte Nährstoffnutzungseffizienz der Pflanzen fokussiert werden. Weidemischkulturen aus Gräsern mit Leguminosen sowie der Einsatz von Kulturen mit speziellen Nährstoffaneignungsstrategien könnten dabei eine große Rolle spielen und sollten in der Region erprobt werden. / La tesis presentada investiga el impacto del establecimiento de pasto, de su fertilización y de su manejo tradicional (abandono del pastizal) a la dinámica del carbono y de los nutrientes de suelo en la región de los bosques tropicales montañosos en el Sur de Ecuador. Durante las últimas décadas el bosque natural en el área de estudio ha estado amenazada por su conversión a pastizales. Sin embargo, la fertilidad del suelo en pastos de tipo extensivo (pastos activos) decrece frecuentemente durante el uso de los pastos. La invasión de Llashipa (Pteridium arachnoideum) conduce al abandono de los pastos cuando la ésta se vuelve dominante. Con la finalidad de revelar los mecanismos detrás de esta disminución de la fertilidad de suelo, se analizaron las propiedades bióticas y abióticas del suelo y sus interacciones, a lo largo de una gradiente del uso de la tierra (bosque natural —pasto activo — pastos abandonados). La perturbación del ecosistema de bosque tropical montañoso por su cambio de uso, mediante el establecimiento de pastizales, ha alterado la función y la estructura de los microorganismos y ha afectado el flujo de CO2‐C del suelo. Cada año 2 Mg CO2‐C ha‐1 fueron emitidas adicionalmente por el establecimiento de pastos. Esta aceleración en la tasa de respiración del suelo está relacionada con el aumento de las tasas de mineralización microbiana de carbono y de la respiración de las raíces. La alta calidad y abundancia de N de los residuos orgánicos del suelo con pasto Mequeron (S. sphacelata, C4‐planta), especialmente debido a la gran biomasa de las raíces finas, ofrecen una disponibilidad alta de C y N para los microorganismos. En comparación con el bosque natural, el aumento del pH y la saturación bases acelerada fueron condiciones más favorables para el crecimiento microbiano y para el metabolismo microbiano en el parte superior del suelo mineral en pastos activos. La cantidad de C de la biomasa de los microorganismos fue tres veces mayor que la del bosque y se ha observado un cambio significativo de la estructura de la comunidad microbiana, en donde la abundancia relativa de los hongos y de las bacterias Gram(‐) ha aumentado. El uso de pasto a largo plazo y la invasión de Llashipa (C3‐planta) han reducido los efectos benéficos para los microorganismos, que resultaron en una reducción significativa de las tasas de la mineralización de C y N, y en una reducción en dos tercios de la biomasa microbiana. El uso preferencial de los microorganismos por sustrato de pasto C4 han resultado en una rápida disminución de la reserva de C4. Como consecuencia, la menor disponibilidad de la reserva de C3 de las plantas de Llashipa y de la cobertura anterior de bosque ha incrementado su dominancia en la reserva de materia orgánica del suelo. Eso resulta, en una mayor disminución de la productividad de los pastos, conduciendo finalmente al abandono de los campos de pastos. La menor calidad y cantidad de los residuos acumulados sobre y bajo el suelo provenientes de la Llashipa han dado como resultado un sustrato de limitadas condiciones que están afectando más a las funciones microbiales antes que a su estructura. La estructura microbiana parece ser más sensible al pH del suelo a largo de la gradiente del uso de la tierra; de manera que se ha identificado una desconexión entre la estructura y función microbial. Experimentos de fertilización en laboratorio y en campo han sido realizados para evaluar el impacto de la aplicación de enmiendas (urea y/o roca fosfórica) a la dinámica de la materia orgánica y a la productividad de los pastos activos. El resultado del experimento de campo ha demostrado que la fertilización combinada es más efectiva, mostrando un aumento en la producción de biomasa de 2 Mg ha−1 a−1, lo que indica una limitación de N y P para el crecimiento del pasto. Además, la calidad de forraje se mostró incrementada ya que el contenido de P y de Ca han aumentado significativamente. Los microorganismos del suelo en el pasto activo han respondido a corto plazo con una adaptación de su estructura ante la disponibilidad de sustrato, pero no han mostrado un cambio de sus funciones iniciales a largo plazo. Después de la aplicación de urea y de la roca fosfórica, se detectó un incremento significativo en la abundancia de los hongos, pero tampoco se observó una limitación de energía microbial ni de N o P. Sin embargo, la aplicación de urea ha aumentado la pérdida gaseosa de CO2‐C del suelo a corto plazo. Debido al cambio de uso de la tierra en la área de investigación, se ha detectado una alteración notable de la función del ecosistema, especialmente en el ciclo de C y N de suelo. Para un uso sostenible de la tierra en esta región, es crucial el prevenir la degradación de pastos y rehabilitar aquellos degradados. En el suelo de pastos activos es de gran importancia el mantener o aún mejor el aumentar la disponibilidad del sustrato, que es uno de los indicadores de la fertilidad del suelo. En este contexto, la materia orgánica se debe ser retenida a largo plazo para mantener la actividad y biomasa microbiana alta y por ende la productividad de pasto. Una moderada fertilización con urea y roca fosfórica puede ser un primer paso para proveer un continuo suministro de nutrientes por el crecimiento del pasto y para reforzar la sanidad pecuaria por medio de un forraje de mayor calidad. Sin embargo, el riesgo de emisiones adicionales de CO2‐C del suelo debido a una aplicación más alta de urea debe tenerse en cuenta. Se puede concluir que para un manejo sostenible del uso de la tierra, tanto el control de la invasión de Llashipa y como un suministro adecuado de nutrientes son necesarios. Adicionalmente se podría decir que es necesario profundizar el estudio de la reducción de las pérdidas de los nutrientes de suelo y de la eficiencia del uso de los nutrientes en las plantas, así como las asociaciones de pastos con leguminosas o el uso de cultivos de absorción selectiva de nutrientes, que serían estrategias importantes para el futuro.

In the present thesis, implications of pasture establishment, fertilization and abandonment on soil C and nutrient dynamics were investigated for the mountain rainforest region of southern Ecuador. Over the past decades the natural forest of the study area has been threatened by conversion to cattle pastures. However, the soil fertility of these extensively grazed pastures (active pastures) declines continuously during pasture use. The invasion of bracken fern (Pteridium arachnoideum) leads to pasture abandonment when bracken becomes dominant. In order to reveal the mechanisms behind the deterioration of soil fertility, biotic and abiotic soil properties and their interaction were analyzed along a land‐use gradient (natural forest – active pasture – abandoned pasture). The ecosystem disturbance of the mountain rainforest through pasture use changed the microbial function and structure, and affected soil CO2‐C fluxes. Annually, 2 Mg soil CO2‐C ha‐1 were additionally emitted from the pasture land. This acceleration in soil respiration rates was related to accelerated rates of microbial C mineralization and fine‐root respiration. The high‐quality, N‐rich above‐ and belowground residues of the pasture grass (S. sphacelata, C4‐plant), especially the huge fine‐root biomass, provided a high C and N availability for soil microbes. Compared to the forest, increased soil pH and accelerated base saturation were further factors beneficial for soil microbial growth and metabolism of the upper mineral soil at active pastures. Three times higher amounts of microbial biomass C and a significant shift in the microbial community structure towards a higher relative abundance of Gram(‐)‐ bacteria and fungi were observed. Long‐term pasture use and the invasion of bracken (C3‐plant) diminished beneficial effects for microbes, causing a significant decrease in the C, net, and gross N mineralization rates as well as a two‐third reduction in the microbial biomass. A preferential substrate utilization of grass‐derived C4 by the soil microbes resulted in a rapid decline of the C4‐pool. As a consequence, the less available C3‐pool from bracken and former forest increased its dominance in the SOC‐pool, further decreasing pasture productivity and finally causing pasture abandonment. The lower quality and quantity of above‐ and belowground residues of the bracken (high lignin content, C/N) resulted in resource‐limited conditions that influenced the microbial function to greater extent than their structure. The microbial structure seemed to be sensitive mainly to soil pH along the land‐use gradient. Thus, a disconnection between microbial structure and function was identified. Fertilization experiments were conducted both in the lab and in the field to evaluate the impact of urea and/or rock phosphate amendment on SOM dynamics and on pasture productivity of active pastures. After combined fertilization the pasture yield was most efficiently increased by 2 Mg ha−1 a−1, indicating a NP‐limitation of grass growth. Furthermore, the fodder quality was improved by a higher content of P and Ca in the grass biomass. The microorganisms of the active pasture soil responded with an adaptation of their structure to the increased substrate availability in the short term, but did not change their initial functions in the long term. After urea/ rock phosphate addition a significant increase in the relative fungal abundance was detected, but neither a microbial limitation of energy nor of N or P was observed. However, urea addition accelerated gaseous losses of soil CO2‐C in the short term. In the study area, pronounced alterations in ecosystem functioning due to land‐use changes were detected, especially in soil C and N cycling rates. For a sustainable land‐use in this region it is crucial to prevent pasture degradation and to rehabilitate degraded pastures in order to protect the prevailing mountain rainforest ecosystem. It is of crucial importance for active pasture soils to maintain or even increase resource availability, being one indicator of soil fertility. In this context, the soil organic matter has to be retained in the long‐term to maintain high microbial activity and biomass, and thus pasture productivity. A moderate fertilization with urea and rock phosphate can be a first step to provide continuous nutrient supply for grass growth and to strengthen livestock health through increased fodder quality. However, the risk of further additional emissions of soil CO2‐C due to increased loads of urea fertilizer application has to be kept in mind. Overall, for the establishment of a sustainable land‐use management the control of bracken invasion and an adjusted nutrient management are needed. Further investigations on the reduction of soil nutrient losses and increased nutrient use efficiencies of plants, such as combined planting with legumes or the usage of cultivars with special nutrient acquisition strategies, should be in the focus of future work.:Contents Acknowledgement I Table of content III List of Tables V List of Figures VI Abbreviations VII Summary (English/German/Spanish) .................................................... 1 1 Introduction ................................................................................... 6 1.1 Impact of land‐use changes on C and nutrient dynamics ............... 6 1.1.1 Soil organic carbon and soil CO2 flux 7 1.1.2 The role of soil microbes 8 1.1.3 Plant‐microbe interactions 10 1.1.4 Impact of soil environment on soil microbes 11 1.2 Pasture establishment in the tropics .......................................... 13 1.3 Research area ....................................................................... .... 15 2 Objectives and research questions ......................... ................... 19 2.1 Land‐use change ........................................................................ 19 2.2 Pasture management ............................................................. ... 21 3 Methodology ................................................................................. 22 3.1 Study sites ............................................................................... 22 3.1.1 Land‐use gradient 22 3.1.2 Pasture Fertilization Experiment (FERPAST) 23 3.2 General analyses ....................................................................... 24 3.2.1 Laboratory experiments 25 3.2.2 In situ measurements 26 3.2.3 Statistics 27 4 Results ............................................................................................ 28 4.1 Soil C and nutrient dynamics along a land‐use gradient ............. 28 Potthast, K., Hamer, U., Makeschin, F., 2011. Land‐use change in a tropical mountain rainforest region of southern Ecuador affects soil microorganisms and nutrient cycling. Biogeochemistry, 1‐17. 4.2 Impact of pH and ongoing succession on microbial function and structure .......... 29 4.3 Response of soil microbes to bracken‐invasion ........................... 32 Potthast K., Hamer U., Makeschin F. 2010. Impact of litter quality on mineralization processes in managed and abandoned pasture soils in Southern Ecuador. Soil Biology and Biochemistry 42, 56‐64. 4.4 Response of soil microbes and pasture grass to fertilization ........33 Hamer, U., Potthast, K., Makeschin, F., 2009. Urea fertilisation affected soil organic matter dynamics and microbial community structure in pasture soils of Southern Ecuador. Applied Soil Ecology 43, 226‐233. Potthast, K., Hamer, U., Makeschin, F., 2012. In an Ecuadorian pasture soil the growth of Setaria sphacelata, but not of soil microorganisms, is co‐limited by N and P. Applied Soil Ecology 62, 103‐114. 5 Discussion .................................................................................... 34 5.1 Impact of land‐use changes ...................................................... 34 5.1.1 Soil CO2 fluxes 34 5.1.2 Microbial structure and function 34 5.2 Soil fertility loss of pastures ‐reasons and first prevention steps‐ . 37 5.2.1 Litter decay and SOM dynamics 37 5.2.2 Fertilization and SOM dynamics 39 5.3 Conclusions and Perspectives ...................................................... 42 References ..................................................................................... 46 Curriculum vitae......................................................................... 58 / In der vorliegenden Dissertation werden die Auswirkungen der Weideetablierung, ‐düngung sowie des Verlassens von Weiden auf Bodenkohlenstoff‐ und Nährstoffdynamik in einer tropischen Bergregenwaldregion Ecuadors zusammenfassend dargestellt und diskutiert. Der Naturwald des Untersuchungsgebietes ist seit Jahrzehnten durch Brandrodung und die Umwandlung in extensiv genutztes Weideland (aktive Weide) in seinem flächenhaften Bestand bedroht. Als Problem hat sich der Verlust an Fruchtbarkeit der Weideböden während ihrer Bewirtschaftung herausgestellt. Des Weiteren führt die Einwanderung des Tropischen Adlerfarns (Pteridium arachnoideum, C3‐Pflanze) zu einer Reduktion der oberirdischen Grasbiomasse. Nimmt diese Entwicklung überhand, werden die betroffenen Flächen von den Bauern nicht mehr aktiv genutzt, verlassen und neuer Regenwald gerodet. Um mehr über die Mechanismen der Verringerung der Bodenfruchtbarkeit zu erfahren, wurden biotische und abiotische Bodeneigenschaften und deren Interaktion entlang eines Landnutzungsgradienten (Naturwald – aktive Weide – verlassene Weide) untersucht. Die Zerstörung des Bergregenwaldökosystems und die Überführung der gerodeten Flächen zur Weidebewirtschaftung verändert die Funktion und Struktur der Bodenmikroorganismen und beeinflusst den CO2‐C Fluss aus dem Boden. Jährlich werden 2 t CO2‐C ha‐1 zusätzlich vom Weideland emittiert. Diese Erhöhung der Bodenatmungsraten kann mit erhöhten Raten der mikrobiellen C‐Mineralisierung und Feinwurzelatmung in Verbindung gebracht werden. Das Weidegras (S. sphacelata, C4‐Pflanze) liefert C‐ und N‐reiche ober und unterirdische organische Substanz (z.B. durch die Feinwurzelbiomasse) und trägt damit zu einer Erhöhung der C‐ und N‐Verfügbarkeit für die mikroorganismen bei. Darüber hinaus stellen ein höherer pH‐Wert und eine erhöhte Basensättigung im oberen Mineralboden der aktiven Weide günstige Bedingungen für mikrobielles Wachstum und Metabolismus dar. Als Konsequenz sind die Gehalte an mikrobiellem Biomassekohlenstoff um das Dreifache erhöht und die mikrobiellen Gemeinschaftsstrukturen signifikant in Richtung einer höheren relativen Abundanz der Gram(‐)‐Bakterien und Pilze verschoben. Eine längerfristige Weidebewirtschaftung ohne Kompensation von Nährstoffverlusten sowie die Einwanderung des Tropischen Adlerfarnes verschlechterte die Bedingungen für die Mikroorganismen, was zu einem signifikanten Rückgang des SOC, der Netto‐ und Brutto‐N‐Mineralisierungsraten sowie zu einer Halbierung der mikrobiellen Biomasse führt. Eine bevorzugte Substratnutzung von Graskohlenstoff (C4) durch die Mikroorganismen hat einen schnellen Abbau des C4‐Pools zur Folge. Somit dominiert nun der mikrobiell schlechter verfügbare C3‐Pool den Bodenkohlenstoffpool. Dies führt zu einem weiteren Rückgang der Weideproduktivität und schließlich zum Offenlassen der Weide. Die geringere Qualität und Quantität der vom Farn stammenden ober‐ und unterirdischen organischen Substanz (hoher Ligninanteil, weites C/N), führten zu einer Limitierung der Ressourcen für die Mikroorganismen, welche deren Funktionen in größerem Maße beeinflussen als deren Gemeinschaftsstruktur. Im Gegensatz dazu wird entlang des Landnutzungsgradienten die Struktur hauptsächlich durch den pH‐Wert beeinflusst. Daraus folgt, dass Struktur und Funktion der Bodenmikroorganismen voneinander entkoppelt auf Veränderungen reagieren können. Um den Einfluss von Harnstoff‐ und/ oder Rohphosphatdüngung aktiver Weiden auf die Dynamik der organischen Bodensubstanz und auf die Weideproduktivität zu untersuchen, wurden sowohl Labor‐ als auch Feldversuche durchgeführt. Im Feldexperiment wurde gezeigt, dass eine NP‐Limitierung der Grasbiomasseproduktion vorliegt und durch eine geringe NP‐Kombinationsdüngung die oberirdische Phytomasseproduktion um 2 t ha−1 a−1 gesteigert und die Futterqualität durch eine Erhöhung der P‐ und Ca‐ Gehalte verbessert werden kann. Die Mikroorganismen reagierten mit einer Anpassung ihrer Struktur an die kurzzeitig erhöhte Substratverfügbarkeit. Nach Gabe von Harnstoff und/ oder Rohphosphat wurde weder eine N‐ noch eine P‐Limitierung der Bodenmikroorganismen festgestellt, und die mikrobiellen Funktionen wurden langfristig nicht verändert. Dagegen bewirkte die Düngergabe einen erhöhten relativen Anteil der Pilzabundanz. Im Labor sowie im Feld kam es nach Harnstoffdüngung kurzzeitig zu verstärkten gasförmigen Verlusten des Bodenkohlenstoffs. Aufgrund der Landnutzungsänderungen im Untersuchungsgebiet veränderten sich die Ökosystemfunktionen stark, speziell die Boden‐C‐ und Boden‐N‐Umsatzraten. Für eine nachhaltige Landnutzung in der Region, d. h., für den Schutz der noch verbliebenen natürlichen Bergregenwaldflächen, ist es von entscheidender Bedeutung, dass die Weidedegradierung verhindert wird und degradierte Flächen wieder in Nutzung genommen werden. Als entscheidend für die Weideproduktivität hat sich in dieser Studie die Ressourcenverfügbarkeit für Bodenmikroorganismen herausgestellt. Daher ist es sehr wichtig, diese Ressourcenverfügbarkeit in Böden aktiv‐genutzter Weiden zu erhalten oder noch zu erhöhen, denn sie wirkt sich vor allem auf die organische Bodensubstanz und im Wechselspiel damit auf die mikrobielle Biomasse und Aktivität aus. Eine moderate Kombinationsdüngung aus Harnstoff und Rohphosphat ist ein erster Schritt in diese Richtung. Dabei sollte jedoch das Risiko zusätzlicher bodenbürtiger CO2‐C Emissionen in Folge höherer Düngergaben berücksichtigt werden. Für ein nachhaltiges Landnutzungsmanagement sind Maßnahmen gegen die Einwanderung des Adlerfarnes und ein angepasstes Nährstoffmanagement notwendig. Weitere Untersuchungen sollten auf eine Minimierung der Nährstoffverluste und eine erhöhte Nährstoffnutzungseffizienz der Pflanzen fokussiert werden. Weidemischkulturen aus Gräsern mit Leguminosen sowie der Einsatz von Kulturen mit speziellen Nährstoffaneignungsstrategien könnten dabei eine große Rolle spielen und sollten in der Region erprobt werden.:Contents Acknowledgement I Table of content III List of Tables V List of Figures VI Abbreviations VII Summary (English/German/Spanish) .................................................... 1 1 Introduction ................................................................................... 6 1.1 Impact of land‐use changes on C and nutrient dynamics ............... 6 1.1.1 Soil organic carbon and soil CO2 flux 7 1.1.2 The role of soil microbes 8 1.1.3 Plant‐microbe interactions 10 1.1.4 Impact of soil environment on soil microbes 11 1.2 Pasture establishment in the tropics .......................................... 13 1.3 Research area ....................................................................... .... 15 2 Objectives and research questions ......................... ................... 19 2.1 Land‐use change ........................................................................ 19 2.2 Pasture management ............................................................. ... 21 3 Methodology ................................................................................. 22 3.1 Study sites ............................................................................... 22 3.1.1 Land‐use gradient 22 3.1.2 Pasture Fertilization Experiment (FERPAST) 23 3.2 General analyses ....................................................................... 24 3.2.1 Laboratory experiments 25 3.2.2 In situ measurements 26 3.2.3 Statistics 27 4 Results ............................................................................................ 28 4.1 Soil C and nutrient dynamics along a land‐use gradient ............. 28 Potthast, K., Hamer, U., Makeschin, F., 2011. Land‐use change in a tropical mountain rainforest region of southern Ecuador affects soil microorganisms and nutrient cycling. Biogeochemistry, 1‐17. 4.2 Impact of pH and ongoing succession on microbial function and structure .......... 29 4.3 Response of soil microbes to bracken‐invasion ........................... 32 Potthast K., Hamer U., Makeschin F. 2010. Impact of litter quality on mineralization processes in managed and abandoned pasture soils in Southern Ecuador. Soil Biology and Biochemistry 42, 56‐64. 4.4 Response of soil microbes and pasture grass to fertilization ........33 Hamer, U., Potthast, K., Makeschin, F., 2009. Urea fertilisation affected soil organic matter dynamics and microbial community structure in pasture soils of Southern Ecuador. Applied Soil Ecology 43, 226‐233. Potthast, K., Hamer, U., Makeschin, F., 2012. In an Ecuadorian pasture soil the growth of Setaria sphacelata, but not of soil microorganisms, is co‐limited by N and P. Applied Soil Ecology 62, 103‐114. 5 Discussion .................................................................................... 34 5.1 Impact of land‐use changes ...................................................... 34 5.1.1 Soil CO2 fluxes 34 5.1.2 Microbial structure and function 34 5.2 Soil fertility loss of pastures ‐reasons and first prevention steps‐ . 37 5.2.1 Litter decay and SOM dynamics 37 5.2.2 Fertilization and SOM dynamics 39 5.3 Conclusions and Perspectives ...................................................... 42 References ..................................................................................... 46 Curriculum vitae......................................................................... 58 / La tesis presentada investiga el impacto del establecimiento de pasto, de su fertilización y de su manejo tradicional (abandono del pastizal) a la dinámica del carbono y de los nutrientes de suelo en la región de los bosques tropicales montañosos en el Sur de Ecuador. Durante las últimas décadas el bosque natural en el área de estudio ha estado amenazada por su conversión a pastizales. Sin embargo, la fertilidad del suelo en pastos de tipo extensivo (pastos activos) decrece frecuentemente durante el uso de los pastos. La invasión de Llashipa (Pteridium arachnoideum) conduce al abandono de los pastos cuando la ésta se vuelve dominante. Con la finalidad de revelar los mecanismos detrás de esta disminución de la fertilidad de suelo, se analizaron las propiedades bióticas y abióticas del suelo y sus interacciones, a lo largo de una gradiente del uso de la tierra (bosque natural —pasto activo — pastos abandonados). La perturbación del ecosistema de bosque tropical montañoso por su cambio de uso, mediante el establecimiento de pastizales, ha alterado la función y la estructura de los microorganismos y ha afectado el flujo de CO2‐C del suelo. Cada año 2 Mg CO2‐C ha‐1 fueron emitidas adicionalmente por el establecimiento de pastos. Esta aceleración en la tasa de respiración del suelo está relacionada con el aumento de las tasas de mineralización microbiana de carbono y de la respiración de las raíces. La alta calidad y abundancia de N de los residuos orgánicos del suelo con pasto Mequeron (S. sphacelata, C4‐planta), especialmente debido a la gran biomasa de las raíces finas, ofrecen una disponibilidad alta de C y N para los microorganismos. En comparación con el bosque natural, el aumento del pH y la saturación bases acelerada fueron condiciones más favorables para el crecimiento microbiano y para el metabolismo microbiano en el parte superior del suelo mineral en pastos activos. La cantidad de C de la biomasa de los microorganismos fue tres veces mayor que la del bosque y se ha observado un cambio significativo de la estructura de la comunidad microbiana, en donde la abundancia relativa de los hongos y de las bacterias Gram(‐) ha aumentado. El uso de pasto a largo plazo y la invasión de Llashipa (C3‐planta) han reducido los efectos benéficos para los microorganismos, que resultaron en una reducción significativa de las tasas de la mineralización de C y N, y en una reducción en dos tercios de la biomasa microbiana. El uso preferencial de los microorganismos por sustrato de pasto C4 han resultado en una rápida disminución de la reserva de C4. Como consecuencia, la menor disponibilidad de la reserva de C3 de las plantas de Llashipa y de la cobertura anterior de bosque ha incrementado su dominancia en la reserva de materia orgánica del suelo. Eso resulta, en una mayor disminución de la productividad de los pastos, conduciendo finalmente al abandono de los campos de pastos. La menor calidad y cantidad de los residuos acumulados sobre y bajo el suelo provenientes de la Llashipa han dado como resultado un sustrato de limitadas condiciones que están afectando más a las funciones microbiales antes que a su estructura. La estructura microbiana parece ser más sensible al pH del suelo a largo de la gradiente del uso de la tierra; de manera que se ha identificado una desconexión entre la estructura y función microbial. Experimentos de fertilización en laboratorio y en campo han sido realizados para evaluar el impacto de la aplicación de enmiendas (urea y/o roca fosfórica) a la dinámica de la materia orgánica y a la productividad de los pastos activos. El resultado del experimento de campo ha demostrado que la fertilización combinada es más efectiva, mostrando un aumento en la producción de biomasa de 2 Mg ha−1 a−1, lo que indica una limitación de N y P para el crecimiento del pasto. Además, la calidad de forraje se mostró incrementada ya que el contenido de P y de Ca han aumentado significativamente. Los microorganismos del suelo en el pasto activo han respondido a corto plazo con una adaptación de su estructura ante la disponibilidad de sustrato, pero no han mostrado un cambio de sus funciones iniciales a largo plazo. Después de la aplicación de urea y de la roca fosfórica, se detectó un incremento significativo en la abundancia de los hongos, pero tampoco se observó una limitación de energía microbial ni de N o P. Sin embargo, la aplicación de urea ha aumentado la pérdida gaseosa de CO2‐C del suelo a corto plazo. Debido al cambio de uso de la tierra en la área de investigación, se ha detectado una alteración notable de la función del ecosistema, especialmente en el ciclo de C y N de suelo. Para un uso sostenible de la tierra en esta región, es crucial el prevenir la degradación de pastos y rehabilitar aquellos degradados. En el suelo de pastos activos es de gran importancia el mantener o aún mejor el aumentar la disponibilidad del sustrato, que es uno de los indicadores de la fertilidad del suelo. En este contexto, la materia orgánica se debe ser retenida a largo plazo para mantener la actividad y biomasa microbiana alta y por ende la productividad de pasto. Una moderada fertilización con urea y roca fosfórica puede ser un primer paso para proveer un continuo suministro de nutrientes por el crecimiento del pasto y para reforzar la sanidad pecuaria por medio de un forraje de mayor calidad. Sin embargo, el riesgo de emisiones adicionales de CO2‐C del suelo debido a una aplicación más alta de urea debe tenerse en cuenta. Se puede concluir que para un manejo sostenible del uso de la tierra, tanto el control de la invasión de Llashipa y como un suministro adecuado de nutrientes son necesarios. Adicionalmente se podría decir que es necesario profundizar el estudio de la reducción de las pérdidas de los nutrientes de suelo y de la eficiencia del uso de los nutrientes en las plantas, así como las asociaciones de pastos con leguminosas o el uso de cultivos de absorción selectiva de nutrientes, que serían estrategias importantes para el futuro.:Contents Acknowledgement I Table of content III List of Tables V List of Figures VI Abbreviations VII Summary (English/German/Spanish) .................................................... 1 1 Introduction ................................................................................... 6 1.1 Impact of land‐use changes on C and nutrient dynamics ............... 6 1.1.1 Soil organic carbon and soil CO2 flux 7 1.1.2 The role of soil microbes 8 1.1.3 Plant‐microbe interactions 10 1.1.4 Impact of soil environment on soil microbes 11 1.2 Pasture establishment in the tropics .......................................... 13 1.3 Research area ....................................................................... .... 15 2 Objectives and research questions ......................... ................... 19 2.1 Land‐use change ........................................................................ 19 2.2 Pasture management ............................................................. ... 21 3 Methodology ................................................................................. 22 3.1 Study sites ............................................................................... 22 3.1.1 Land‐use gradient 22 3.1.2 Pasture Fertilization Experiment (FERPAST) 23 3.2 General analyses ....................................................................... 24 3.2.1 Laboratory experiments 25 3.2.2 In situ measurements 26 3.2.3 Statistics 27 4 Results ............................................................................................ 28 4.1 Soil C and nutrient dynamics along a land‐use gradient ............. 28 Potthast, K., Hamer, U., Makeschin, F., 2011. Land‐use change in a tropical mountain rainforest region of southern Ecuador affects soil microorganisms and nutrient cycling. Biogeochemistry, 1‐17. 4.2 Impact of pH and ongoing succession on microbial function and structure .......... 29 4.3 Response of soil microbes to bracken‐invasion ........................... 32 Potthast K., Hamer U., Makeschin F. 2010. Impact of litter quality on mineralization processes in managed and abandoned pasture soils in Southern Ecuador. Soil Biology and Biochemistry 42, 56‐64. 4.4 Response of soil microbes and pasture grass to fertilization ........33 Hamer, U., Potthast, K., Makeschin, F., 2009. Urea fertilisation affected soil organic matter dynamics and microbial community structure in pasture soils of Southern Ecuador. Applied Soil Ecology 43, 226‐233. Potthast, K., Hamer, U., Makeschin, F., 2012. In an Ecuadorian pasture soil the growth of Setaria sphacelata, but not of soil microorganisms, is co‐limited by N and P. Applied Soil Ecology 62, 103‐114. 5 Discussion .................................................................................... 34 5.1 Impact of land‐use changes ...................................................... 34 5.1.1 Soil CO2 fluxes 34 5.1.2 Microbial structure and function 34 5.2 Soil fertility loss of pastures ‐reasons and first prevention steps‐ . 37 5.2.1 Litter decay and SOM dynamics 37 5.2.2 Fertilization and SOM dynamics 39 5.3 Conclusions and Perspectives ...................................................... 42 References ..................................................................................... 46 Curriculum vitae......................................................................... 58