京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第21150号 / 農博第2276号 / 新制||農||1059(附属図書館) / 学位論文||H30||N5124(農学部図書室) / 京都大学大学院農学研究科地域環境科学専攻 / (主査)教授 北山 兼弘, 教授 小杉 緑子, 教授 本田 与一 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第21842号 / 農博第2355号 / 新制||農||1069(附属図書館) / 学位論文||H31||N5214(農学部図書室) / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 大澤 晃, 教授 神﨑 護, 教授 井鷺 裕司 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

Root-feeding insects can have top-down influence on vegetative composition and ecosystem processes; however, they may respond to bottom-up factors such as soil resources, site productivity, and disturbance.  My research addressed the following questions: (1) Do disturbance (fire), vegetative composition, soil resources, and fine root standing mass influence the structure of root-feeding insect assemblages? (2) What types of roots do root-feeding insects eat, and do they forage selectively?  (3) Do root-feeding insects influence fine root productivity?  To address these questions, I studied root-feeding insect assemblages in longleaf pine wiregrass (Pinus palustris-Aristida stricta) ecosystems of southwestern Georgia, U.S.A.  On a random basis, study sites were burned at least every other year (B), or left unburned (UB) for about 9 years.  Fine root productivity and root-feeding insect abundances were sampled repeatedly across 54 random plots in UB and B sites.  In Chapter 2, I characterized spatial and temporal patterns of root-feeding insect abundance, understory plant composition, soil resource availability, and fine root standing mass within each plot.  Insect population densities were low overall, but abundance, patchiness, and diversity were greater in UB sites.  Abundance patterns were significantly related to vegetative composition.  In Chapter 3, I quantified the diet of root-feeding insects by measuring the natural abundance of carbon (C) and nitrogen (N) stable isotopes in insects and fine roots.  Using 13C abundance, I examined the contribution of warm season grass roots to insect diet, relative to the proportion of warm season grass roots within adjacent root standing crop samples; 15N abundance was used to detect omnivory.  Overall, insects appeared to be non-selective herbivores and omnivores that may alter foraging behavior to maintain a mixed diet (i.e. reducing or increasing warm season grass consumption when its abundance was high or low, respectively).  The extent of omnivory varied within and among taxa.  In Chapter 4, I estimated the top-down influence of root-feeding insects on fine root productivity by comparison of ingrowth cores with or without an insecticide treatment.  I detected a weak positive effect of herbivores on the productivity of non-grass fine roots (< 10% of fine root productivity). / Ph. D.

Forests account for a large portion of global carbon storage. Almost half of this carbon is stored underground. Roots, especially fine-roots (diameter ≤ 2 mm) are an important part of soil carbon, and play a number of ecological roles. Yet, the below-ground parts of trees are still poorly understood. The aim of this report was to understand environmental controls over plants traits. I tested if plants shift their root traits towards a resource conservative strategy when environmental conditions are challenging (dry and cold). Furthermore, the contribution of different fine-root diameters to total root length (TRL), surface area (SA) and root volume (VO) was assessed. Root traits such as TRL, SA, VO, fine-root diameter, specific root length (SRL) and root tissue density (RTD) were quantified. The root samples are taken from 11 old growth Swedish forests across a climate gradient in three different soil moisture categories per forest (dry, intermediate, wet). Fine-roots were scanned, and analysed with the RhizoVision Explorer Software (Version 2.0.3). Uni-factorial ANOVAs, combined with Tukey’s posthoc test, or linear regressions were conducted, and the results revealed no significant effects of the summer air temperature on root traits. However, higher soil moisture was found to decrease RTD, but increase fine-root diameters significantly. These findings did not confirm the plants aim on building resource conservative root traits in challenging conditions. Instead, they highlighted variability among and within forests suggest that multiple factors influence root morphology and function. This study contributes to our understanding of how fine-roots respond to environmental conditions.

No description available.

Afin de garantir une gestion durable du massif forestier des Landes de Gascogne (maintien de la fertilité et production élevée), des études sont nécessaires sur la biodisponibilité du phosphore (P) qui est un facteur limitant. Une évaluation fiable de la biodisponibilité du P passe par la quantification des processus d’acquisition par les plantes, à savoir l’interception racinaire, le transport dans la solution et la mobilisation à l’interface solide-solution d’ions phosphates. Dans ce contexte, l’objectif général de la thèse était de faire un bilan biogéochimique de la biodisponibilité du P dans les sols forestiers des Landes de Gascogne, c'est-à-dire une analyse quantitative et comparative des processus physico- chimiques (diffusion) et biologiques (minéralisation et reminéralisation) de réapprovisionnement de la solution en ions phosphates ainsi qu’une caractérisation du système de prélèvement (racines fines) du Pin maritime. Les résultats ont montré une déficience en P pour l’ensemble des sols étudiés. Ils ont également montré une importance variable, en fonction de la profondeur et du type de lande (humide à sèche), des différents processus biologiques et physico-chimiques dans le réapprovisionnement de la solution. Le rôle des micro-organismes, via la minéralisation du P organique du sol et en tant que source (reminéralisation) et puits (immobilisation) de P, est particulièrement important dans les sols peu réactifs vis-à-vis du P comme les litières ou certains sols minéraux de surface. L’étude du système de prélèvement (racines fines, ectomycorhizes) suggère que le prélèvement de P par le Pin maritime concerne aussi bien les horizons de surface que ceux du sous-sol. / In order to guarantee a sustainable management of the forest range the “Landes de Gascogne” (maintaining fertility and elevated productivity), the bioavailability of phosphorus (P), a growth limiting factor, needs to be studied. An accurate evaluation of P bioavailability implies the quantification of plant acquisition processes such as root interception, soil solution transport and the mobilisation of phosphate ions at the soil-soil solution interface. The main objective of the PhD study was to assess a biogeochemical balance of the P bioavailability in the forest soils of the “Landes de Gascogne”, i.e. to carry out an quantitative and comparative analysis of the physical-chemical (diffusion) and biological (mineralization and remineralization) processes of replenishing the soil solution with phosphate ions, as well as the characterisation of the tree uptake system (fine roots) of maritime pine. The results have shown that all of the soils studied are very deficient in P. They have further shown a varying importance of the different biological and physical-chemical processes in supplying P to the soil solution according to the site class (humid to dry moorlands). The role of the microorganisms, via the mineralization of organic P, as a source (remineralization) or a sink (immobilization) of P, is particularly important in the litter and top mineral layers featuring a very low reactivity versus P. The study of the uptake system (fine roots and ectomycorrhizae) suggests that uptake of P by maritime pine takes place both in top soil horizons and in deeper soil horizons.

No description available.

The Southern Appalachian hardwood forests contain a wide diversity of flora and fauna. Understanding processes that affect nutrient availability in these forests is essential for sound forest management. Three interconnected research projects regarding soil resource heterogeneity were designed to increase our understanding of this ecosystem. The objective of these projects were as follows: 1) to examine and quantify the role of decaying stumps in regards to total carbon (C) and nitrogen (N) pools and fine-root dynamics, 2) compare and contrast the use of ground-penetrating radar (GPR) vs. a soil auger for estimating soil depth and site quality and 3) to evaluate how eastern red-backed salamanders (Plethodon cinereus) affect N-availability. For the stump study, results show that decomposing stumps occupy approximately 1.2% of the total soil volume and constitute 4% and 10% of total soil N and C pools. Significant differences in N (p = 0.0114), C (p = 0.0172), microbial biomass C (p = 0.0004), potentially mineralizable N (p = 0.0042), and extractable NH4+ (p = 0.0312) concentrations were observed when compared to mineral soil horizons. In particular, potentially mineralizable N was 2.5 times greater in stump soil than the A-horizon (103 vs. 39 mg kg-1), 2.7 times greater for extractable NH4+ (16 vs. 6 mg kg-1) and almost 4 times greater for MBC (1528 vs. 397 mg kg-1). These measured properties suggest higher N-availability, organic matter turnover and N uptake in stump soil versus the bulk soil. 19% of the total fine root length and 14% of fine root surface area also occurred in the stump soil. The increased fine root length suggests higher concentrations of labile nutrient in the stumps since roots often proliferate in areas with higher nutrient availability. Significant differences occurred in N and C concentrations between all four decay classes and the A-horizon, which validated the use of this system and the need to calculate weighted averages based on the frequency and soil volume influenced by each decay class. In the GPR Study, depth estimations were shallower using a soil auger compared to estimates obtained using GPR across all plots (p = 0.0002; Figure 3.4). On a soil volume basis, this was equivalent to about 3500 m3 of soil per hectare unaccounted for using traditional methods. In regards to using soil depth as a predictor for site quality, no significant relationships were observed with soil depth estimations obtained from the auger (Table 3.3). On the other hand, depth measurements from GPR explained significant amounts of variation across all sites and by physiographic region. Across all sites, soil depth estimates from GPR explained 45.5% of the residual variation (p = 0.001; Table 3.3). When the data were stratified by physiographic region, a higher amount of variation was explained by the regression equations; 85% for the Cumberland Plateau (p = 0.009), 86.7% for the Allegheny Plateau (0.007) and 66.7% for the Ridge and Valley (p = 0.013), respectively (Table 4.2). Results from this study demonstrate how inaccurate current methods can be for estimating soil depth rocky forests soils. Furthermore, depth estimations from GPR can be used to increase the accuracy of site quality in the southern Appalachians. In the salamander study, no significant salamander density treatment or treatment by time effects were observed over the entire study period (p < 0.05). However, when the data were separated by individual sampling periods a few significant treatment by time interactions occurred: 1) during August 2006 for available NH4+ under the forest floor (i.e. horizontal cation membranes; p = 0.001), 2) August and 3) September 2006 for available NH4+ in the A-horizon (p = 0.026), and 4) May 2007 for available NO3- under the forest floor (p = 0.011). As a result of these trends, an index of cumulative N-availability (i.e. NH4+ and NO3-) under the forest floor and in the A-horizon was examined through the entire study period. Cumulative N-availability under the forest floor was consistently higher in the low- and medium-density salamander treatments compared to the high-density treatment. For cumulative N-availability in the A-horizon, a gradient of high to low N-availability existed as salamander density increased. Factors such as a prolonged drought in 2007 may have affected our ability to accurately assess the effects of salamanders on N-availability. We concluded that higher salamander densities do not increase N-availability. Implementing methodologies that accurately account for soil nutrient pools such as stump soil, physical properties such as depth and fauna such as salamanders, increase our understanding of factors that regulate site productivity in these ecosystems. As a result, landscape-level and stand-level management decisions can be conducted more effectively. / Ph. D.

Tropical forests restoration is an important tool for climate change mitigation and biodiversity conservation. We can ally both of these elements, according to the biodiversity and ecosystem (BEF) functioning theory, which says that diversity enhances ecosystem functions, as primary productivity. Nevertheless, the greatest part of BEF studies up to very recently have focused on grasslands and not on as complex ecosystems as tropical forests. It is necessary to better understand above- and below-ground processes through which biodiversity acts on ecosystem functions. This work aimed to investigate effects of tree richness on both above- and below-ground ecological processes. It was based on two tropical forests undergoing restoration, in Sardinilla (Panama) and in Anhembi (Brazil). The former was especially designed for BEF studies and allowed to untangle effects of biodversity on ecosystem functions. The latter had more than a hundred species in plots and permitted investigation of the effects of high tree richness levels. In both Sardinilla and Anhembi, we investigated if tree richness levels affected an above-ground ecological process, light interception, and which mechanisms could be related to it. Richness could enhance light interception and mechanisms as spatial (horizontal and vertical) and temporal light distribution. It promoted both selection and complementarity effects. In Anhembi, we investigated if species richness influenced below-ground processes related to soil carbon stocks. Stand richness enhanced fine root production and stock. Effects of stand number of species on litter decomposition and stock were not linear. Richness of litter content, however, did not affect its decomposition rates. Number of stand species did not influence litter production. Differences of litter production, stock and fine root production among distinct richness levels did not change over the time. However, distribution of fine roots over the space, within different layers of soil, was affected by number of tree species. We concluded that even very high richness levels could not saturate some of the ecological processes studied. Diversity acted on both above- and below-ground processes, in various and sometimes opposite ways, counting on multi-direction feedbacks. It is very important to understand these mechanisms in order to potencialize biodiversity convervation and carbon sequestration by tropical forest restoration. Future studies may focus on untangling effects of diversity on below-ground processes (which have not been exhaustively explored in research), on understanding how high diversity levels affects natural regeneration and on investigationg functional traits provided by different species. / A restauração de florestas tropicais é uma importante ferramenta para a mitigação de mudanças climáticas e conservação de biodiversidade. Essas duas medidas podem ser aliadas, de acordo com a teoria de biodiversidade e funcionamento de ecossistemas (BEF, do inglês: biodiversity and ecosystem functioning), segundo a qual a diversidade pode favorecer funções do ecossistema, como a produtividade primária. Entretanto, a maior parte dos estudos de BEF até muito recentemente focaram em campos de gramíneas e não em ecossistemas tão complexos quanto florestas tropicais. É necessário entender tanto processos acima quanto abaixo do solo pelos quais a biodiversidade atua no funcionamento de ecossistemas. Este trabalho teve como objetivo verificar o efeito da riqueza de espécies arbóreas em processes ecológicos acima e abaixo do solo. Ele se baseou em duas áreas de estudo, em Sardinilla (Panamá) e em Anhembi (Brasil). A primeira foi especialmente projetada para estudos de BEF e permitiu destrinchar efeitos da biodiversidade em funções do ecossistema. A segunda possuía parcelas com mais de cem espécies, permitindo explorar os efeitos de altos níveis de riqueza. Tanto em Sardinilla quanto em Anhembi, investigamos se a riqueza de espécies arbóreas influenciou um processo ecológico acima do solo, a interceptação de luz, bem como mecanismos que podem estar associados a ele. A riqueza de espécies aumentou a interceptação de luz pelo dossel e estimulou mecanismos como a distribuição de luz ao longo do espaço (horizontal e vertical) e tempo. Ela promoveu tanto efeito de seleção quanto de complementaridade. Na área de Anhembi, investigamos se a riqueza de espécies influenciou processes abaixo do solo relacionados ao estoque de carbono nesse compartimento. A riqueza no dossel aumentou a produção e o estoque de raízes finas. Número de espécies do dossel teve efeito não linear sobre taxas de decomposição e estoque de serapilheira. A riqueza do conteúdo da serapilheira, contudo, não influenciou sua decomposição. O número de espécies do dossel também não influenciou a produção de serapilheira. As diferenças de produção e estoque de serapilheira e de produção de raízes finas, entre diferentes níveis de riquezas, não se alteraram ao longo do tempo. Contudo, o número de espécies arbóreas promoveu maior distribuição de raízes finas em diferentes camadas do solo. Concluímos que elevados níveis de riqueza não saturaram alguns processes ecológicos estudados. A diversidade foi capaz de atuar em processos tanto acima quanto abaixo do solo, por vários meios, muitas vezes em sentidos opostos, contando com feedbacks multidirecionais. É muito importante entender esses mecanismos para potencializar a conservação da biodiversidade e a provisão de funções ecossistêmicas, no processo de restauração de florestas tropicais, em um contexto internacional de necessidade de mitigação de mudanças climáticas. Estudos futuros devem focar em efeitos da diversidade em processos abaixo do solo (que são os menos abordados em estudos até o momento), em entender como altos níveis de diversidade podem afetar a regeneração natural em florestas e em explorar os atributos funcionais apresentados por cada espécie.

Tropical forests restoration is an important tool for climate change mitigation and biodiversity conservation. We can ally both of these elements, according to the biodiversity and ecosystem (BEF) functioning theory, which says that diversity enhances ecosystem functions, as primary productivity. Nevertheless, the greatest part of BEF studies up to very recently have focused on grasslands and not on as complex ecosystems as tropical forests. It is necessary to better understand above- and below-ground processes through which biodiversity acts on ecosystem functions. This work aimed to investigate effects of tree richness on both above- and below-ground ecological processes. It was based on two tropical forests undergoing restoration, in Sardinilla (Panama) and in Anhembi (Brazil). The former was especially designed for BEF studies and allowed to untangle effects of biodversity on ecosystem functions. The latter had more than a hundred species in plots and permitted investigation of the effects of high tree richness levels. In both Sardinilla and Anhembi, we investigated if tree richness levels affected an above-ground ecological process, light interception, and which mechanisms could be related to it. Richness could enhance light interception and mechanisms as spatial (horizontal and vertical) and temporal light distribution. It promoted both selection and complementarity effects. In Anhembi, we investigated if species richness influenced below-ground processes related to soil carbon stocks. Stand richness enhanced fine root production and stock. Effects of stand number of species on litter decomposition and stock were not linear. Richness of litter content, however, did not affect its decomposition rates. Number of stand species did not influence litter production. Differences of litter production, stock and fine root production among distinct richness levels did not change over the time. However, distribution of fine roots over the space, within different layers of soil, was affected by number of tree species. We concluded that even very high richness levels could not saturate some of the ecological processes studied. Diversity acted on both above- and below-ground processes, in various and sometimes opposite ways, counting on multi-direction feedbacks. It is very important to understand these mechanisms in order to potencialize biodiversity convervation and carbon sequestration by tropical forest restoration. Future studies may focus on untangling effects of diversity on below-ground processes (which have not been exhaustively explored in research), on understanding how high diversity levels affects natural regeneration and on investigationg functional traits provided by different species. / A restauração de florestas tropicais é uma importante ferramenta para a mitigação de mudanças climáticas e conservação de biodiversidade. Essas duas medidas podem ser aliadas, de acordo com a teoria de biodiversidade e funcionamento de ecossistemas (BEF, do inglês: biodiversity and ecosystem functioning), segundo a qual a diversidade pode favorecer funções do ecossistema, como a produtividade primária. Entretanto, a maior parte dos estudos de BEF até muito recentemente focaram em campos de gramíneas e não em ecossistemas tão complexos quanto florestas tropicais. É necessário entender tanto processos acima quanto abaixo do solo pelos quais a biodiversidade atua no funcionamento de ecossistemas. Este trabalho teve como objetivo verificar o efeito da riqueza de espécies arbóreas em processes ecológicos acima e abaixo do solo. Ele se baseou em duas áreas de estudo, em Sardinilla (Panamá) e em Anhembi (Brasil). A primeira foi especialmente projetada para estudos de BEF e permitiu destrinchar efeitos da biodiversidade em funções do ecossistema. A segunda possuía parcelas com mais de cem espécies, permitindo explorar os efeitos de altos níveis de riqueza. Tanto em Sardinilla quanto em Anhembi, investigamos se a riqueza de espécies arbóreas influenciou um processo ecológico acima do solo, a interceptação de luz, bem como mecanismos que podem estar associados a ele. A riqueza de espécies aumentou a interceptação de luz pelo dossel e estimulou mecanismos como a distribuição de luz ao longo do espaço (horizontal e vertical) e tempo. Ela promoveu tanto efeito de seleção quanto de complementaridade. Na área de Anhembi, investigamos se a riqueza de espécies influenciou processes abaixo do solo relacionados ao estoque de carbono nesse compartimento. A riqueza no dossel aumentou a produção e o estoque de raízes finas. Número de espécies do dossel teve efeito não linear sobre taxas de decomposição e estoque de serapilheira. A riqueza do conteúdo da serapilheira, contudo, não influenciou sua decomposição. O número de espécies do dossel também não influenciou a produção de serapilheira. As diferenças de produção e estoque de serapilheira e de produção de raízes finas, entre diferentes níveis de riquezas, não se alteraram ao longo do tempo. Contudo, o número de espécies arbóreas promoveu maior distribuição de raízes finas em diferentes camadas do solo. Concluímos que elevados níveis de riqueza não saturaram alguns processes ecológicos estudados. A diversidade foi capaz de atuar em processos tanto acima quanto abaixo do solo, por vários meios, muitas vezes em sentidos opostos, contando com feedbacks multidirecionais. É muito importante entender esses mecanismos para potencializar a conservação da biodiversidade e a provisão de funções ecossistêmicas, no processo de restauração de florestas tropicais, em um contexto internacional de necessidade de mitigação de mudanças climáticas. Estudos futuros devem focar em efeitos da diversidade em processos abaixo do solo (que são os menos abordados em estudos até o momento), em entender como altos níveis de diversidade podem afetar a regeneração natural em florestas e em explorar os atributos funcionais apresentados por cada espécie.