To date, there has been little research into the role of microbial community structure in the functioning of the soil ecosystem and on the links between microbial biomass size, microbial activity and key soil processes that drive nutrient availability. The maintenance of structural and functional diversity of the soil microbial community is essential to ensure the sustainability of agricultural production systems. Soils of the same type with similar fertility that had been under long-term organic and conventional crop management in Canterbury, New Zealand, were selected to investigate relationships between microbial community composition, function and potential environmental impacts. The effects of different fertilisation strategies on soil biology and nitrogen (N) dynamics were investigated under field (farm site comparison), semi-controlled (lysimeter study) and controlled (incubation experiments) conditions by determining soil microbial biomass carbon (C) and N, enzyme activities (dehydrogenase, arginine deaminase, fluorescein diacetate hydrolysis), microbial community structure (denaturing gradient gel electrophoresis following PCR amplification of 16S and 18S rDNA fragments using selected primer sets) and N dynamics (mineralisation and leaching). The farm site comparison revealed distinct differences between the soils in microbial community structure, microbial biomass C (conventional > organic) and arginine deaminase activity (organic > conventional). In the lysimeter study, the soils were subjected to the same crop rotation (barley (Hordeum vulgare L.), maize (Zea mays L.), rape (Brassica napus L. ssp. oleifera (Moench)) plus a lupin green manure (Lupinus angustifolius L.) and two fertiliser regimes (following common organic and conventional practice). Soil biological properties, microbial community structure and mineral N leaching losses were determined over 2½ years. Differences in mineral leaching losses were not significant between treatments (total organic management: 24.2 kg N per ha; conventional management: 28.6 kg N per ha). Crop rotation and plant type had a larger influence on the microbial biomass, activity and community structure than fertilisation. Initial differences between soils decreased over time for most biological soil properties, while they persisted for the enzyme activities (e.g. dehydrogenase activity: 4.0 and 2.9 µg per g and h for organic and conventional management history, respectively). A lack of consistent positive links between enzyme activities and microbial biomass size indicated that similarly sized and structured microbial communities can express varying rates of activity. In two successive incubation experiments, the soils were amended with different rates of a lupin green manure (4 or 8t dry matter per ha), and different forms of N at 100 kg per ha (urea and lupin) and incubated for 3 months. Samples were taken periodically, and in addition to soil biological properties and community structure, gross N mineralisation was determined. The form of N had a strong effect on microbial soil properties. Organic amendment resulted in a 2 to 5-fold increase in microbial biomass and enzyme activities, while microbial community structure was influenced by the addition or lack of C or N substrate. Correlation analyses suggested treatment-related differences in nutrient availability, microbial structural diversity (species richness or evenness) and physiological properties of the microbial community. The findings of this thesis showed that using green manures and crop rotations improved soil biology in both production systems, that no relationships existed between microbial structure, enzyme activities and N mineralisation, and that enzyme activities and microbial community structure are more closely associated with inherent soil and environmental factors, which makes them less useful as early indicators of changes in soil quality.

Pulses are an important component in crop rotations in the semiarid Brown soil zone of southern Saskatchewan, Canada. Besides their capability to fix nitrogen, pulse crops establish a strong symbiotic relationship with arbuscular mycorrhizal fungi (AMF), which have been shown to increase nutrient and water uptake through hyphal extensions in the soil. Incorporating strongly mycorrhizal crops in a rotation may increase inoculum levels in the soil and benefit the growth of a subsequent crop. The objective of this study was to determine if AMF potential and colonization of a durum crop is significantly affected by cropping history and to assess the impact of pulses in crop rotations on the abundance and diversity of AMF communities in the soil. In 2004 and 2005, soil, plant, and root samples were taken on Triticum turgidum L. (durum) with preceding crops of Pisum sativum L. (pea), Lens culinaris Medik (lentil), Cicer arietinum L. (chickpea), Brassica napus L. (canola) or Triticum turgidum L. (durum). Although there were few differences in soil N and P levels, previous crop had a significant effect (p<0.05) on durum yields in both years. A previous crop of pea was associated with the highest yields, while the durum monocultures were lowest. Arbuscular mycorrhizal potential and colonization were significantly affected (p<0.05) by cropping history, but not consistently as a result of inclusion of a pulse crop. Phospholipid and neutralipid fatty acids (PLFA/NLFA) were completed to analyse the relative abundance of AMF (C16:1ù5), saprophytic fungi (C18:2ù6), and bacteria in the soil. The effect of treatment on the abundance of AMF, saprotrophic fungi and bacteria were not significant (p<0.05), but the changes over time were. These results demonstrate that although previous crop may play a role in microbial community structure, it is not the only influencing factor.

Pulses are an important component in crop rotations in the semiarid Brown soil zone of southern Saskatchewan, Canada. Besides their capability to fix nitrogen, pulse crops establish a strong symbiotic relationship with arbuscular mycorrhizal fungi (AMF), which have been shown to increase nutrient and water uptake through hyphal extensions in the soil. Incorporating strongly mycorrhizal crops in a rotation may increase inoculum levels in the soil and benefit the growth of a subsequent crop. The objective of this study was to determine if AMF potential and colonization of a durum crop is significantly affected by cropping history and to assess the impact of pulses in crop rotations on the abundance and diversity of AMF communities in the soil. In 2004 and 2005, soil, plant, and root samples were taken on Triticum turgidum L. (durum) with preceding crops of Pisum sativum L. (pea), Lens culinaris Medik (lentil), Cicer arietinum L. (chickpea), Brassica napus L. (canola) or Triticum turgidum L. (durum). Although there were few differences in soil N and P levels, previous crop had a significant effect (p<0.05) on durum yields in both years. A previous crop of pea was associated with the highest yields, while the durum monocultures were lowest. Arbuscular mycorrhizal potential and colonization were significantly affected (p<0.05) by cropping history, but not consistently as a result of inclusion of a pulse crop. Phospholipid and neutralipid fatty acids (PLFA/NLFA) were completed to analyse the relative abundance of AMF (C16:1ù5), saprophytic fungi (C18:2ù6), and bacteria in the soil. The effect of treatment on the abundance of AMF, saprotrophic fungi and bacteria were not significant (p<0.05), but the changes over time were. These results demonstrate that although previous crop may play a role in microbial community structure, it is not the only influencing factor.

<p>Treatment wetlands play an important role in reducing nitrogen content in wastewater and agricultural run-off water. The main removal process is denitrification and the removal efficiency depends on the hydrological and microbiological features of the wetland, especially in terms of water residence times and denitrification rates. The aim of this thesis was to increase the understanding of the coupled hydrological and microbiological processes regulating the denitrification capacity. This was done by applying a broad spectrum of analyses methods, including tracer experiment, water flow modeling, denitrification rate measurements, and analyses of the microbial community structures. The tracer experiment and flow modeling revealed that the wetland design, especially the vegetation, largely can affect the water residence time distributions in wetlands. In the investigated wetland, vegetation dominated the water flow, explaining 60-80% of the variance in water residence times, whereas basin shape only explained about 10% of the variance, but also mixing phenomena significantly affected the residence times and could considerably delay solutes. Measured potential denitrification rates in the wetland exhibited significant spatial variations, and the variations were best described by concentration of nitrogen in sediments and water residence time. Analyses of the denitrifying bacteria populations indicated that a few key populations dominated and that the community diversity increased with decreasing nutrient levels and increasing water residence times. Moreover, it was found that denitrification rates in terms of Menten and first order kinetics can be evaluated by fitting a mathematical expression, considering denitrification and other nitrogen transforming processes to measured product formation in nitrate limited experiments.</p>

Take-all is the name given to the disease caused by a soilborne fungus Gaeumannomyces graminis (Sacc.) von Arx and Olivier var. tritici Walker (Ggt), an ascomycete of the family Magnaportheaceae (Cook, 2003). This fungus is an aggressive soil-borne pathogen causing root rot of wheat (primary host), barley and rye crops (secondary host). The flowering, seedling, and vegetative growth stages can be affected by the infection of the whole plant, leaves, roots, and stems. Infections of roots result in losses in crop yield and quality primarily due to a lowering in nutrient uptake. Take-all is most common in regions where wheat is cultivated without adequate crop rotation. Crop rotation allows time between the planting dates of susceptible crops, which causes a decrease in the inoculum potential of soilborne plant pathogens to levels below an economic threshold by resident antagonistic soil microbial communities. Soilborne disease suppressiveness is an inherent characteristic of the physical, chemical, and/or biological structure of a particular soil which might be induced by agricultural practices and activities such as the cultivation of crops, or the addition of organisms or nutritional amendments, causing a change in the microfloral environment. Disturbances of soil ecosystems that impact on the normal functioning of microbial communities are potentially detrimental to soil formation, energy transfers, nutrient cycling, and long-term stability. In this regard, an overview of soil properties and processes indicated that the use of microbiological and biochemical soil properties, such as microbial biomass, the analysis of microbial functional diversity and microbial structural diversity by the quantification of community level physiological profiles and signature lipid biomarkers are useful as indicators of soil ecological stress or restoration properties because they are more responsive to small changes than physical and chemical characteristics. In this study, the relationship between physico-chemical characteristics, and different biological indicators of soil quality of agricultural soils conducive, suppressive, and neutral with respect to take-all disease of wheat as caused by the soilborne fungus Gaeumannomyces graminis var. tritici (Ggt), were investigated using various techniques. The effect of crop rotation on the functional and structural diversity of soils conducive to take-all disease was also investigated. Through the integration of quantitative and qualitative biological data as well as the physico-chemical characteristics of the various soils, the functional and structural diversity of microbial IV communities in the soils during different stadia of take-all disease of wheat were characterised. All results were evaluated statistically and the predominant physical and chemical characteristics that influenced the microbiological and biochemical properties of the agricultural soils during different stadia of take-all disease of wheat were identified using multivariate analyses. Although no significant difference @ > 0.05) could be observed between the various soils using conventional microbiological enumeration techniques, the incidence of Gliocladium spp. in suppressive soils was increased. Significant differences @ < 0.05) were observed between agricultural soils during different stadia of take-all disease of wheat. Although no clear distinction could be made between soils suppressive and neutral to take-all disease of wheat, soils suppressive and conducive to take-all disease of wheat differed substantially in their community level physiological profiles (CLPPs). Soils suppressive / neutral to take-all disease were characterised by enhanced utilisation of carboxylic acids, amino acids, and carbohydrates, while conducive soils were characterised by enhanced utilisation of carbohydrates. Shifts in the functional diversity of the associated microbial communities were possibly caused by the presence of Ggt and associated antagonistic fungal and bacterial populations in the various soils. It was evident that the relationships amongst the functionality of the microbial communities within the various soils had undergone changes through the different stages of development of take-all disease of wheat, thus implying different substrate utilisation capabilities of present soil microbial communities. Diversity indices were calculated as Shannon's diversity index (H') and substrate equitability (J) and were overall within the higher diversity range of 3.6 and 0.8, respectively, indicating the achievement of very high substrate diversity values in the various soils. A substantial percentage of the carbon sources were utilised, which contributed to the very high Shannon-Weaver substrate utilisation indices. Obtained substrate evenness (equitability) (J) indices indicated an existing high functional diversity. The functional diversity as observed during crop rotation, differed significantly (p < 0.05) from each other, implying different substrate utilisation capabilities of present soil microbial communities, which could possibly be ascribed to the excretion of root exudates by sunflowers and soybeans. Using the Sorenson's index, a clear distinction could be made between the degrees of substrate utilisation between microbial populations in soils conducive, suppressive, and neutral to take-all disease of wheat, as well as during crop rotation. Furthermore, the various soils could also be differentiated on the basis of the microbial community structure as determined by phospholipid fatty acid (PLFA) analysis. Soil suppressive to take-all disease of wheat differed significantly (p < 0.05) from soils conducive, and neutral to take-all disease of wheat, implying a shift in relationships amongst the structural diversity of microbial communities within the various soils. A positive association was observed between the microbial phospholipid fatty acid profiles, and dominant environmental variables of soils conducive, suppressive, and neutral to take-all disease of wheat. Soils conducive and neutral to take-all disease of wheat were characterised by high concentrations of manganese, as well as elevated concentrations of monounsaturated fatty acids, terminally branched saturated fatty acids, and polyunsaturated fatty acids which were indicative of Gram-negative bacteria, Gram-positive bacteria and micro eukaryotes (primarily fungi), respectively. These soils were also characterised by low concentrations of phosphorous, potassium, percentage organic carbon, and percentage organic nitrogen, as well as low soil pH. Soil suppressive to take-all disease of wheat was characterised by the elevated levels of estimated of biomass and elevated concentrations of normal saturated fatty acids, which is ubiquitous to micro-organisms. The concentration of normal saturated fatty acids in suppressive soils is indicative of a low structural diversity. This soil was also characterised by high concentrations of phosphorous, potassium, percentage organic carbon, and percentage organic nitrogen, as well as elevated soil pH. The relationship between PLFAs and agricultural soils was investigated using principal component analysis (PCA), redundancy analysis (RDA) and discriminant analysis (DA). Soil suppressive to take-all disease of wheat differed significantly (p < 0.05) from soils conducive, and neutral to take-all disease of wheat, implying a shift in relationships amongst the structural diversity of microbial communities within the various soils. A positive association was observed between the microbial phospholipid fatty acid profiles, and dominant environmental variables of soils conducive, suppressive, and neutral to take-all disease of wheat. Hierarchical cluster analysis of the major phospholipid fatty acid groups indicated that the structural diversity differed significantly between soils conducive, suppressive, and neutral to take-all disease of wheat caused by Gaeumannomyces graminis var. tritici. The results indicate that the microbial community functionality as well as the microbial community structure was significantly influenced by the presence of take-all disease of wheat caused by Gaeumannomyces graminis var. tritici, and that the characterisation of microbial functional and structural diversity by analysis of community level physiological profiles and phospholipid fatty acid analysis, respectively, could be successfully used as an assessment criteria for the evaluation of agricultural soils conducive, suppressive, and neutral to take-all disease of wheat, as well as in crop rotation systems. This methodology might be of significant value in assisting in the management and evaluation of agricultural soils subject to the prevalence of other soilborne diseases. / Thesis (M.Sc. (Microbiology))--North-West University, Potchefstroom Campus, 2004.

The conversion of native forest to agricultural land has been an on-going issue threatening the health of New Zealand’s freshwater systems. However, despite the fact that this has been occurring since early European settlement, our understanding of the mechanistic relationships between riparian vegetation and stream condition are poorly developed. This research investigated: (i) how forests affect downstream benthic macroinvertebrate communities in pasture and the environmental factors driving community change; (ii) how upstream forest size impacted the rate of change in downstream environmental drivers and associated macroinvertebrate community structure; and (iii) whether the addition of coarse particulate organic matter (a single potential driver of forest community structure) can reset community structure to that of a forested state. Physico-chemical conditions, basal energy resources, and macroinvertebrates were surveyed in several New Zealand headwater streams. At Mount Egmont National Park, 10-12 sites were surveyed across a longitudinal forest-pasture gradient in each of five streams flowing from continuous forest to dairy farmland. My results showed that forests can have marked effects downstream. From the forest edge, water temperatures increased consistently, with a rise of approximately 0.2ºC per 100 m of downstream distance. By contrast, coarse particulate organic matter (CPOM) decreased rapidly downstream of the forest, however, low levels of “forest-derived” CPOM were still present 300m downstream from the forest edge. These environmental changes drove significant shifts in macroinvertebrate community structure. Moreover, pasture communities were markedly different from those in forest, despite being only 100 m from the forest edge. In particular, total macroinvertebrate and EPT richness and densities decreased, and communities shifted from evenly distributed allochthonous-based communities to autochthonous-based communities, highly dominated by molluscs (e.g., Potamopyrgus spp.) Subsequent surveys of 6-8 sites across a longitudinal forest-pasture gradient in each of eleven streams flowing from forest fragments of different sizes into grazed pastures throughout the Canterbury region, indicated that stream temperature increased more rapidly downstream of small- and medium-sized fragments, than larger fragments. A Berger-Parker dominance index also indicated that macroinvertebrates responded principally to water temperature, with communities being more highly dominated by temperature-tolerant molluscs in streams flowing from small-sized forest fragments. Several headwater streams in Canterbury were also highly retentive, with marked CPOM rarely exported beyond 50 m downstream of the forest. Experimental additions of leaf litter to the pasture reaches of the same streams dramatically increased amounts of stored benthic CPOM. Although non-significant, trends indicated that EPT and shredder densities increased at litter addition sites, providing promise that CPOM can function as a mechanism directly enhancing healthy stream communities. My findings support the contention that when the replanting of entire stream reaches is infeasible, the use of riparian management strategies which focus on the planting of intermittent patches along stream banks can potentially improve stream habitat and community health downstream.

Take-all is the name given to the disease caused by a soilborne fungus Gaeumannomyces graminis (Sacc.) von Arx and Olivier var. tritici Walker (Ggt), an ascomycete of the family Magnaportheaceae (Cook, 2003). This fungus is an aggressive soil-borne pathogen causing root rot of wheat (primary host), barley and rye crops (secondary host). The flowering, seedling, and vegetative growth stages can be affected by the infection of the whole plant, leaves, roots, and stems. Infections of roots result in losses in crop yield and quality primarily due to a lowering in nutrient uptake. Take-all is most common in regions where wheat is cultivated without adequate crop rotation. Crop rotation allows time between the planting dates of susceptible crops, which causes a decrease in the inoculum potential of soilborne plant pathogens to levels below an economic threshold by resident antagonistic soil microbial communities. Soilborne disease suppressiveness is an inherent characteristic of the physical, chemical, and/or biological structure of a particular soil which might be induced by agricultural practices and activities such as the cultivation of crops, or the addition of organisms or nutritional amendments, causing a change in the microfloral environment. Disturbances of soil ecosystems that impact on the normal functioning of microbial communities are potentially detrimental to soil formation, energy transfers, nutrient cycling, and long-term stability. In this regard, an overview of soil properties and processes indicated that the use of microbiological and biochemical soil properties, such as microbial biomass, the analysis of microbial functional diversity and microbial structural diversity by the quantification of community level physiological profiles and signature lipid biomarkers are useful as indicators of soil ecological stress or restoration properties because they are more responsive to small changes than physical and chemical characteristics. In this study, the relationship between physico-chemical characteristics, and different biological indicators of soil quality of agricultural soils conducive, suppressive, and neutral with respect to take-all disease of wheat as caused by the soilborne fungus Gaeumannomyces graminis var. tritici (Ggt), were investigated using various techniques. The effect of crop rotation on the functional and structural diversity of soils conducive to take-all disease was also investigated. Through the integration of quantitative and qualitative biological data as well as the physico-chemical characteristics of the various soils, the functional and structural diversity of microbial IV communities in the soils during different stadia of take-all disease of wheat were characterised. All results were evaluated statistically and the predominant physical and chemical characteristics that influenced the microbiological and biochemical properties of the agricultural soils during different stadia of take-all disease of wheat were identified using multivariate analyses. Although no significant difference @ > 0.05) could be observed between the various soils using conventional microbiological enumeration techniques, the incidence of Gliocladium spp. in suppressive soils was increased. Significant differences @ < 0.05) were observed between agricultural soils during different stadia of take-all disease of wheat. Although no clear distinction could be made between soils suppressive and neutral to take-all disease of wheat, soils suppressive and conducive to take-all disease of wheat differed substantially in their community level physiological profiles (CLPPs). Soils suppressive / neutral to take-all disease were characterised by enhanced utilisation of carboxylic acids, amino acids, and carbohydrates, while conducive soils were characterised by enhanced utilisation of carbohydrates. Shifts in the functional diversity of the associated microbial communities were possibly caused by the presence of Ggt and associated antagonistic fungal and bacterial populations in the various soils. It was evident that the relationships amongst the functionality of the microbial communities within the various soils had undergone changes through the different stages of development of take-all disease of wheat, thus implying different substrate utilisation capabilities of present soil microbial communities. Diversity indices were calculated as Shannon's diversity index (H') and substrate equitability (J) and were overall within the higher diversity range of 3.6 and 0.8, respectively, indicating the achievement of very high substrate diversity values in the various soils. A substantial percentage of the carbon sources were utilised, which contributed to the very high Shannon-Weaver substrate utilisation indices. Obtained substrate evenness (equitability) (J) indices indicated an existing high functional diversity. The functional diversity as observed during crop rotation, differed significantly (p < 0.05) from each other, implying different substrate utilisation capabilities of present soil microbial communities, which could possibly be ascribed to the excretion of root exudates by sunflowers and soybeans. Using the Sorenson's index, a clear distinction could be made between the degrees of substrate utilisation between microbial populations in soils conducive, suppressive, and neutral to take-all disease of wheat, as well as during crop rotation. Furthermore, the various soils could also be differentiated on the basis of the microbial community structure as determined by phospholipid fatty acid (PLFA) analysis. Soil suppressive to take-all disease of wheat differed significantly (p < 0.05) from soils conducive, and neutral to take-all disease of wheat, implying a shift in relationships amongst the structural diversity of microbial communities within the various soils. A positive association was observed between the microbial phospholipid fatty acid profiles, and dominant environmental variables of soils conducive, suppressive, and neutral to take-all disease of wheat. Soils conducive and neutral to take-all disease of wheat were characterised by high concentrations of manganese, as well as elevated concentrations of monounsaturated fatty acids, terminally branched saturated fatty acids, and polyunsaturated fatty acids which were indicative of Gram-negative bacteria, Gram-positive bacteria and micro eukaryotes (primarily fungi), respectively. These soils were also characterised by low concentrations of phosphorous, potassium, percentage organic carbon, and percentage organic nitrogen, as well as low soil pH. Soil suppressive to take-all disease of wheat was characterised by the elevated levels of estimated of biomass and elevated concentrations of normal saturated fatty acids, which is ubiquitous to micro-organisms. The concentration of normal saturated fatty acids in suppressive soils is indicative of a low structural diversity. This soil was also characterised by high concentrations of phosphorous, potassium, percentage organic carbon, and percentage organic nitrogen, as well as elevated soil pH. The relationship between PLFAs and agricultural soils was investigated using principal component analysis (PCA), redundancy analysis (RDA) and discriminant analysis (DA). Soil suppressive to take-all disease of wheat differed significantly (p < 0.05) from soils conducive, and neutral to take-all disease of wheat, implying a shift in relationships amongst the structural diversity of microbial communities within the various soils. A positive association was observed between the microbial phospholipid fatty acid profiles, and dominant environmental variables of soils conducive, suppressive, and neutral to take-all disease of wheat. Hierarchical cluster analysis of the major phospholipid fatty acid groups indicated that the structural diversity differed significantly between soils conducive, suppressive, and neutral to take-all disease of wheat caused by Gaeumannomyces graminis var. tritici. The results indicate that the microbial community functionality as well as the microbial community structure was significantly influenced by the presence of take-all disease of wheat caused by Gaeumannomyces graminis var. tritici, and that the characterisation of microbial functional and structural diversity by analysis of community level physiological profiles and phospholipid fatty acid analysis, respectively, could be successfully used as an assessment criteria for the evaluation of agricultural soils conducive, suppressive, and neutral to take-all disease of wheat, as well as in crop rotation systems. This methodology might be of significant value in assisting in the management and evaluation of agricultural soils subject to the prevalence of other soilborne diseases. / Thesis (M.Sc. (Microbiology))--North-West University, Potchefstroom Campus, 2004.

Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / A introdução de espécies invasoras marinhas tem causado danos econômicos e ecológicos consideráveis em todo o mundo. Algumas destas espécies incluindo corais escleractíneos possuem adaptações, tais como metabólitos secundários utilizados para evitar a predação e competição por espaço por outros organismos. Este arsenal químico e as interações entre espécies invasoras e nativas podem causar alterações na distribuição das espécies e na estrutura das comunidades de costões rochosos tropicais. Os objetivos deste estudo foram (1) caracterizar os metabólitos secundários produzidos pelos corais invasores Tubastraea tagusensis e T. coccinea na Baía da Ilha Grande, Brasil, (2) detectar os compostos químicos liberados pelos tecidos de Tubastraea tagusensis in situ utilizando um aparelho submersível; (3) testar no campo os extratos metanólicos produzidos por ambas as espécies de Tubastraea contra a predação por peixes generalistas e assentamento de outros organismos, (4) testar no campo se os compostos químicos produzidos por ambos os corais invasores variaram na concentração ou tipo quando os corais foram colocados próximos de competidores nativos e (5) determinar como as comunidades de costões rochosos da Baía da Ilha Grande foram afetadas pela expansão de Tubastraea coccinea e T. tagusensis em 8 locais estudados durante 2 anos. As principais classes de substâncias encontradas nos extratos metanólicos de Tubastraea foram identificados como esteróis, ácidos graxos, hidrocarbonetos, alcalóides, ésteres e alcoóis, entretanto, o aparelho submersível identificou somente hidrocarbonetos liberados por Tubastraea na água do mar. O extrato metanólico de T. tagusensis reduziu a predação por peixes generalistas e já os extratos de ambas as espécies mostraram efeitos espécie-específicos sobre organismos incrustantes no campo. No experimento de interação competitiva foi detectada a presença de necrose nos tecidos do coral endêmico Mussismilia hispida e isso provocou variação nas concentrações de esteróis, alcalóides e ácidos graxos nos tecidos de Tubastraea. Em contraste, a esponja Desmapsamma anchorata cresceu sobre os tecidos das colônias de ambos os corais invasores. A presença de Tubastraea nas comunidades bentônicas causou uma dissimilaridade média de 4,8% nas comunidades invadidas. Uma forte relação positiva foi encontrada entre a cobertura de Tubastraea e a mudança na estrutura da comunidade da Baía da Ilha Grande. Portanto, os efeitos negativos de ambos os corais invasores são suficientes para acarretar mudanças na estrutura das comunidades bentônicas tropicais. / Invasive marine species has caused economic and ecological damage around the world. Some scleractinian corals possess secondary metabolites used to avoid predation and to help them in competition for space with other organisms. The negative action of chemical substances in the interactions between invasive and native species may produce changes on community structure in tropical rocky shores. This study showed (1) the secondary metabolites produced by the invasive corals Tubastraea tagusensis and T. coccinea in Ilha Grande Bay, Brazil; (2) chemical compounds released by Tubastraea tagusensis tissues in situ using a submersible apparatus; (3) the action of MeOH extracts produced by both species of Tubastraea against predation by generalist fish and settlement of other organisms in the field; (4) variation on class and concentration of chemical compounds produced by these invasive corals when these species were placed in proximity to native competitors and (5) changes on rocky shore community structure due to expansion of Tubastraea coccinea and T. tagusensis after 2 years of study. The main classes of compounds detected by GC / MS in the MeOH extracts of Tubastraea were identified as sterols, fatty acids, hydrocarbons, alkaloids, esters and alcohols. The submersible apparatus identified only hydrocarbons released by Tubastraea in situ. The MeOH extract of T. tagusensis reduced generalist fish predation and the MeOH extracts of both Tubastraea species showed species-specific effects on fouling organisms in the field. The competition experiment showed necrosis in the tissues of the native coral Mussismilia hispida and variation in sterols, alkaloids and fatty acid concentrations in Tubastraea tissues. The opposite behavior was sawn, the sponge Desmapsamma anchorata overgrew Tubastraea colonies. The presence of Tubastraea in the benthic communities caused a mean dissimilarity of 4.8% in the invaded communities. A positive relationship between invader cover and change in Ilha Grande community structure was found and, therefore, Tubastraea is a threat to native benthic communities throughout the tropical Oceans.

The investigation of the hidden metric space behind complex network topologies is a fervid topic in current network science and the hyperbolic space is one of the most studied, because it seems associated to the structural organization of many real complex systems. The popularity-similarity-optimization (PSO) model simulates how random geometric graphs grow in the hyperbolic space, generating realistic networks with clustering, small-worldness, scale-freeness and rich-clubness. However, it misses to reproduce an important feature of real complex networks, which is the community organization. The geometrical-preferential-attachment (GPA) model was recently developed in order to confer to the PSO also a soft community structure, which is obtained by forcing different angular regions of the hyperbolic disk to have a variable level of attractiveness. However, the number and size of the communities cannot be explicitly controlled in the GPA, which is a clear limitation for real applications. Here, we introduce the nonuniform PSO (nPSO) model. Differently from GPA, the nPSO generates synthetic networks in the hyperbolic space where heterogeneous angular node attractiveness is forced by sampling the angular coordinates from a tailored nonuniform probability distribution (for instance a mixture of Gaussians). The nPSO differs from GPA in other three aspects: it allows one to explicitly fix the number and size of communities; it allows one to tune their mixing property by means of the network temperature; it is efficient to generate networks with high clustering. Several tests on the detectability of the community structure in nPSO synthetic networks and wide investigations on their structural properties confirm that the nPSO is a valid and efficient model to generate realistic complex networks with communities.

Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / A introdução de espécies invasoras marinhas tem causado danos econômicos e ecológicos consideráveis em todo o mundo. Algumas destas espécies incluindo corais escleractíneos possuem adaptações, tais como metabólitos secundários utilizados para evitar a predação e competição por espaço por outros organismos. Este arsenal químico e as interações entre espécies invasoras e nativas podem causar alterações na distribuição das espécies e na estrutura das comunidades de costões rochosos tropicais. Os objetivos deste estudo foram (1) caracterizar os metabólitos secundários produzidos pelos corais invasores Tubastraea tagusensis e T. coccinea na Baía da Ilha Grande, Brasil, (2) detectar os compostos químicos liberados pelos tecidos de Tubastraea tagusensis in situ utilizando um aparelho submersível; (3) testar no campo os extratos metanólicos produzidos por ambas as espécies de Tubastraea contra a predação por peixes generalistas e assentamento de outros organismos, (4) testar no campo se os compostos químicos produzidos por ambos os corais invasores variaram na concentração ou tipo quando os corais foram colocados próximos de competidores nativos e (5) determinar como as comunidades de costões rochosos da Baía da Ilha Grande foram afetadas pela expansão de Tubastraea coccinea e T. tagusensis em 8 locais estudados durante 2 anos. As principais classes de substâncias encontradas nos extratos metanólicos de Tubastraea foram identificados como esteróis, ácidos graxos, hidrocarbonetos, alcalóides, ésteres e alcoóis, entretanto, o aparelho submersível identificou somente hidrocarbonetos liberados por Tubastraea na água do mar. O extrato metanólico de T. tagusensis reduziu a predação por peixes generalistas e já os extratos de ambas as espécies mostraram efeitos espécie-específicos sobre organismos incrustantes no campo. No experimento de interação competitiva foi detectada a presença de necrose nos tecidos do coral endêmico Mussismilia hispida e isso provocou variação nas concentrações de esteróis, alcalóides e ácidos graxos nos tecidos de Tubastraea. Em contraste, a esponja Desmapsamma anchorata cresceu sobre os tecidos das colônias de ambos os corais invasores. A presença de Tubastraea nas comunidades bentônicas causou uma dissimilaridade média de 4,8% nas comunidades invadidas. Uma forte relação positiva foi encontrada entre a cobertura de Tubastraea e a mudança na estrutura da comunidade da Baía da Ilha Grande. Portanto, os efeitos negativos de ambos os corais invasores são suficientes para acarretar mudanças na estrutura das comunidades bentônicas tropicais. / Invasive marine species has caused economic and ecological damage around the world. Some scleractinian corals possess secondary metabolites used to avoid predation and to help them in competition for space with other organisms. The negative action of chemical substances in the interactions between invasive and native species may produce changes on community structure in tropical rocky shores. This study showed (1) the secondary metabolites produced by the invasive corals Tubastraea tagusensis and T. coccinea in Ilha Grande Bay, Brazil; (2) chemical compounds released by Tubastraea tagusensis tissues in situ using a submersible apparatus; (3) the action of MeOH extracts produced by both species of Tubastraea against predation by generalist fish and settlement of other organisms in the field; (4) variation on class and concentration of chemical compounds produced by these invasive corals when these species were placed in proximity to native competitors and (5) changes on rocky shore community structure due to expansion of Tubastraea coccinea and T. tagusensis after 2 years of study. The main classes of compounds detected by GC / MS in the MeOH extracts of Tubastraea were identified as sterols, fatty acids, hydrocarbons, alkaloids, esters and alcohols. The submersible apparatus identified only hydrocarbons released by Tubastraea in situ. The MeOH extract of T. tagusensis reduced generalist fish predation and the MeOH extracts of both Tubastraea species showed species-specific effects on fouling organisms in the field. The competition experiment showed necrosis in the tissues of the native coral Mussismilia hispida and variation in sterols, alkaloids and fatty acid concentrations in Tubastraea tissues. The opposite behavior was sawn, the sponge Desmapsamma anchorata overgrew Tubastraea colonies. The presence of Tubastraea in the benthic communities caused a mean dissimilarity of 4.8% in the invaded communities. A positive relationship between invader cover and change in Ilha Grande community structure was found and, therefore, Tubastraea is a threat to native benthic communities throughout the tropical Oceans.