细菌群落主导沙漠公路防护林营造后的土壤功能变化

防护林作为沙漠公路的安全保护屏障,其生长和应对胁迫所需的养分供给依赖于土壤微生物。以塔里木沙漠公路防护林和自然沙漠为研究系统,探究土壤细菌和真菌群落、两种生境共有和特有微生物物种变化对土壤物质循环功能的驱动作用。结果显示,土壤细菌和真菌物种丰富度(P ＜ 0.01, P ＜ 0.01)及群落组成(P ＜ 0.05, P ＜ 0.01)均受防护林营造的显著影响,细菌物种丰富度的响应增幅为77.5%,高于真菌22.1%。细菌群落是导致土壤酶活性升高的显著驱动因素,而非真菌群落或环境因子;细菌物种丰富度(rho=0.46, P ＜ 0.01)和群落组成(rho=0.68, P ＜ 0.01)与土壤酶之间呈显著偏Mantel相关。共有细菌相对丰度(rho=0.47, P ＜ 0.01)和特有细菌物种丰富度(rho=0.36, P ＜ 0.01)是驱动土壤酶活性改善的关键因素,与土壤酶之间呈显著偏Mantel相关。研究表明,沙漠公路防护林土壤细菌而非真菌主导微生物群落的响应,细菌群落通过改变本地物种丰度和新物种数量来调控土壤功能。     

Soil chemical properties,rather than landscape context,influence woodland fungal communities along an urban‐rural gradient

With the expansion of cities around the world there is a growing interest in the factors that influence biodiversity and ecosystem processes in urban areas. Fungi are exceptionally diverse and play key roles in ecosystem function, yet despite predictions of negative impacts due to urbanization, fungi have been generally overlooked in urban ecological studies. We surveyed fungi in 16 remnant river red gum (Eucalyptus camaldulensis: Myrtaceae) woodlands along a gradient of 4–35 km from the city of Melbourne (south‐east Australia). Using both sporocarp surveys and terminal restriction fragment length polymorphism (T‐RFLP; primer pair ITS1‐F‐ITS4), we examined relationships between fungal community composition, landscape context (i.e. urbanization) and soil physicochemical properties. Community compositions from sporocarp data were significantly correlated with those from T‐RFLP data, largely because of correlations with ectomycorrhizal sporocarps (Spearman rank correlation coefficients ρ 0.31–0.42) rather than saprotrophic fungi (ρ 0.18–0.21). Principal components analysis of soil properties and non‐metric multidimensional scaling ordinations of fungal community composition showed no clear separation of sites according to urbanization, and there were no significant correlations between fungal community composition and urbanization. However, fungal community composition was significantly correlated with soil chemical properties (ρ 0.41–0.55). These data suggest that site‐scale soil properties, and associated effects of past and current land management activities, were more important in determining fungal community composition than the landscape‐level influences of urbanization.     

Soil-wood interactions: Influence of decaying coniferous and broadleaf logs on composition of soil fungal communities

Wood-inhabiting fungi may affect soil fungal communities directly underneath decaying wood via their exploratory hyphae. In addition, differences in wood leachates between decaying tree species may influence soil fungal communities. We determined the composition of fungi in 4-yr old decaying logs of Larix kaempferi and Quercus rubra as well as in soil directly underneath and next to logs. Fungal community composition in soil covered by logs was different from that in wood and uncovered soil and was clearly influenced by the tree species. Soil fungal species richness under logs was lower than in uncovered soil but higher than in decaying wood. The amount of exploratory hyphae of log-inhabiting fungi was only high close to decaying logs. In conclusion, there is a small but significant effect of decaying coniferous and broadleaf logs on soil fungal communities directly underneath logs, likely affected by differences in wood chemistry and fungal preference between tree species.     

Evidence that niche specialization explains species-energy relationships in lake fish communities

1. Interspecific niche differences have long been identified as a major explanation for the occurrence of species-rich communities. However, much fieldwork studying variation in local species richness has focused upon physical habitat attributes or regional factors, such as the size of the regional species pool. 2. We applied indices of functional diversity and niche overlap to data on the species niche to examine the importance of interspecific niche differentiation for species richness in French lake fish communities. We combined this information with environmental data to test generalizations of the physiological tolerance and niche specialization hypotheses for species-energy relationships. 3. We found evidence for a largely non-saturating relationship (relative to random expectation) between species richness and functional evenness (evenness of spacing between species in niche space), while functional richness (volume of niche space occupied) peaked at moderate levels of species richness and niche overlap showed an initial decrease followed by saturation. This suggests that increased niche specialization may have allowed species to coexist in the most species-rich communities. 4. We tested for evidence that increased temperature, local habitat area, local habitat diversity and immigration affected species richness via increased niche specialization. Temperature explained by far the largest amount of variation in species richness, functional diversity and niche overlap. These results, combined with the largely non-saturating species richness-functional evenness relationship, suggest that increased temperature may have permitted increased species richness by allowing increased niche specialization. 5. These results emphasize the importance of niche differences for species coexistence in species-rich communities, and indicate that the conservation of functional diversity may be vital for the maintenance of species diversity in biological communities. Our approach may be applied readily to many types of community, and at any scale, thus providing a flexible means of testing niche-based hypotheses for species richness gradients.     

Disentangling the roles of chance,abiotic factors and biotic interactions among epiphytic bryophyte communities in a tropical rainforest (Yunnan,China)

• Epiphytes offer an appealing framework to disentangle the contributions of chance, biotic and abiotic drivers of species distributions. In the context of the stress-gradient theory, we test the hypotheses that (i) deterministic (i.e., non-random) factors play an increasing role in communities from young to old trees, (ii) negative biotic interactions increase on older trees and towards the tree base, and (iii) positive interactions show the reverse pattern.
• Bryophyte species distributions and abiotic conditions were recorded on a 1.1 ha tropical rainforest canopy crane site. We analysed co-occurrence patterns in a niche modelling framework to disentangle the roles of chance, abiotic factors and putative biotic interactions among species pairs.
• 76% of species pairs resulted from chance. Abiotic factors explained 78% of non-randomly associated species pairs, and co-occurrences prevailed over non-coincidences in the remaining species pairs. Positive and negative interactions mostly involved species pairs from the same versus different communities (mosses versus liverworts) and life forms, respectively. There was an increase in randomly associated pairs from large to small trees. No increase in negative interactions from young to old trees or from the canopy to the base was observed.
• Our results suggest that epiphytic bryophyte community composition is primarily driven by environmental filtering, whose importance increases with niche complexity and diversity. Biotic interactions play a secondary role, with a very marginal contribution of competitive exclusion. Biotic interactions vary among communities (mosses versus liverworts) and life forms, facilitation prevailing among species from the same community and life form, and competition among species from different communities and life forms.

     

Niche separation and weak interactions in the high tidal zone of saltmarsh‐mangrove mixing communities

1. Saltmarsh‐mangrove ecotones occur at the boundary of the natural geographic distribution of mangroves and salt marshes. Climate warming and species invasion can also drive the formation of saltmarsh‐mangrove mixing communities. How these coastal species live together in a “new” mixed community is important in predicting the dynamic of saltmarsh‐mangrove ecosystems as affected by ongoing climate change or human activities. To date, the understanding of species interactions has been rare on adult species in these ecotones.
2. Two typical coastal wetlands were selected as cases to understand how mangrove and saltmarsh species living together in the ecotones. The leaves of seven species were sampled from these coastal wetlands based on their distribution patterns (living alone or coexisting) in the high tidal zone, and seven commonly used functional traits of these species were analyzed.
3. We found niche separation between saltmarsh and mangrove species, which is probably due to the different adaptive strategies they adopted to deal with intertidal environments.
4. Weak interactions between coexisting species were dominated in the high tidal zone of the two saltmarsh‐mangrove communities, which could be driven by both niche differentiation and neutral theory.
5. Synthesis. Our field study implies a potential opportunity to establish a multispecies community in the high tidal zone of saltmarsh‐mangrove ecotones, where the sediment was characterized by low salinity and high nitrogen.

     

Abiotic drivers and plant traits explain landscape‐scale patterns in soil microbial communities

The controls on aboveground community composition and diversity have been extensively studied, but our understanding of the drivers of belowground microbial communities is relatively lacking, despite their importance for ecosystem functioning. In this study, we fitted statistical models to explain landscape‐scale variation in soil microbial community composition using data from 180 sites covering a broad range of grassland types, soil and climatic conditions in England. We found that variation in soil microbial communities was explained by abiotic factors like climate, pH and soil properties. Biotic factors, namely community‐weighted means (CWM) of plant functional traits, also explained variation in soil microbial communities. In particular, more bacterial‐dominated microbial communities were associated with exploitative plant traits versus fungal‐dominated communities with resource‐conservative traits, showing that plant functional traits and soil microbial communities are closely related at the landscape scale.