Soil fungi and bacteria are the key players in the transformation and processing of carbon and nutrients in terrestrial ecosystems, yet controls on their abundance and activity are not well ...understood. Based on stoichiometric principles, soil microbial processes are expected to be limited by mineral nutrients, which are particularly scarce in often highly weathered tropical forest soils. Such limitation is directly relevant for the fate of soil carbon and global element cycles, but its extent and nature have never been assessed systematically across the tropical biome. Here, we address the relative importance of nitrogen, phosphorus, and other nutrients in limiting soil microbial biomass and process rates in tropical forests. We conducted an in-depth literature review and a meta-analysis of the available nutrient addition experiments in tropical forests worldwide. Our synthesis showed predominant and general phosphorus limitation of a variety of microbial processes across tropical forests, and additional nitrogen limitation in tropical montane forests. The apparent widespread microbial phosphorus limitation needs to be accounted for in the understanding and prediction of biogeochemical cycles in tropical forests and their future functioning. Other mineral nutrients or carbon may modify the importance of phosphorus, but more experimental studies are urgently needed.
Climate and plant litter diversity are major determinants of carbon (C) and nitrogen (N) cycling rates during decomposition. Yet, how these processes will be modified with combined changes in climate ...and biodiversity is poorly understood. With a multisite field experiment, we studied the interactive effects of reinforced and prolonged summer drought (using rainout shelters) and tree species mixing on leaf litter decomposition in beech forests in the French Alps. Forests included monospecific stands of
Fagus sylvatica
,
Abies alba
and
Quercus pubescens
and two-species mixtures composed of beech and one of the other species. We hypothesized (1) slower C and N release during decomposition in response to experimentally prolonged summer drought, but (2) less so in mixed compared to monospecific tree stands, due to indirect canopy effects and direct litter mixing effects. Litter lost 35% of initial C and 15% of N on average across all sites and litter types over 30 months of decomposition. The experimentally prolonged summer drought led to weakly slower C loss but had no effect on N loss. Tree species mixing did not alter drought effects on decomposition but had non-additive effects on C and N loss, which were dominated by direct litter mixing rather than indirect plot-specific tree species composition effects. Our data suggest relatively small effects of reinforced and prolonged summer drought on decomposition, possibly because process rates are generally slow during summer and because microsite variability is larger than the effects of rainfall exclusion. The dominant contribution of litter mixing to the overall effect of plot-specific tree species mixtures on decomposition supports the importance of microsite conditions for C and N dynamics during decomposition, which should be accounted for more explicitly in climate and biodiversity change predictions.
Plant species diversity affects carbon and nutrient cycling during litter decomposition, yet the generality of the direction of this effect and its magnitude remains uncertain. With a meta-analysis ...including 65 field studies across the Earth's major forest ecosystems, we show here that decomposition was faster when litter was composed of more than one species. These positive biodiversity effects were mostly driven by temperate forests but were more variable in other forests. Litter mixture effects emerged most strongly in early decomposition stages and were related to divergence in litter quality. Litter diversity also accelerated nitrogen, but not phosphorus release, potentially indicating a decoupling of nitrogen and phosphorus cycling and perhaps a shift in ecosystem nutrient limitation with changing biodiversity. Our findings demonstrate the importance of litter diversity effects for carbon and nutrient dynamics during decomposition, and show how these effects vary with litter traits, decomposer complexity and forest characteristics.
1. Ecological stoichiometry predicts important control of the relative abundance of the key elements carbon (C), nitrogen (N) and phosphorus (P) on trophic interactions. In a nutrient-poor Amazonian ...lowland rain forest of French Guiana, we tested the hypothesis that decomposers exploit stoichiometrically diverse plant litter more efficiently, resulting in faster litter decomposition compared to litter with a uniform stoichiometry. 2. In a field experiment in the presence or absence of soil macrofauna, we measured litter mass loss, and N and P dynamics from all possible combinations of leaf litter from four common tree species which were distinctly separated along a C:N and along a N:P gradient. 3. Mean litter mass remaining after 204 days of field exposure varied between 25.2% and 71.3% among litter treatments. Fauna increased litter mass loss by 18%, N loss by 21% and P loss by 14%. Litter species richness had no effect on litter mass loss or nutrient dynamics. In contrast, litter mass and nutrient losses increased with increasing stoichiometric dissimilarity of litter mixtures in presence of fauna, suggesting faster decomposition of a stoichiometrically more heterogeneous litter. 4. However, the effect of stoichiometric dissimilarity was smaller than the strong C quality related litter composition effect and disappeared in the absence of fauna. Increasing proportions of litter that is relatively rich in accessible C compounds (non-structural carbohydrates, phenolics) and relatively poor in recalcitrant C (condensed tannins, lignin), correlated best with litter mass loss irrespective of fauna presence. No correlation was found for any of the nutrient related litter quality parameters and decomposition. 5.Synthesis. Our results suggest that Amazonian decomposer communities studied here are primarily limited by energy, and only secondarily by litter stoichiometry. Tropical tree species might thus influence decomposers and detritivores by the production of litter of specific C quality with potentially important feedback effects on ecosystem nutrient dynamics and availability.
Different tree species influence litter decomposition directly through species-specific litter traits, and indirectly through distinct modifications of the local decomposition environment. Whether ...these indirect effects on decomposition are influenced by tree species diversity is presently not clear.
We addressed this question by studying the decomposition of two common substrates, cellulose paper and wood sticks, in a total of 209 forest stands of varying tree species diversity across six major forest types at the scale of Europe.
Tree species richness showed a weak but positive correlation with the decomposition of cellulose but not with that of wood. Surprisingly, macroclimate had only a minor effect on cellulose decomposition and no effect on wood decomposition despite the wide range in climatic conditions among sites from Mediterranean to boreal forests. Instead, forest canopy density and stand-specific litter traits affected the decomposition of both substrates, with a particularly clear negative effect of the proportion of evergreen tree litter.
Our study suggests that species richness and composition of tree canopies modify decomposition indirectly through changes in microenvironmental conditions. These canopy-induced differences in the local decomposition environment control decomposition to a greater extent than continental-scale differences in macroclimatic conditions.
Plant litter decomposition is a key process in terrestrial carbon cycling, yet the relative importance of various control factors remains ambiguous at a global scale. A full reciprocal litter ...transplant study with 16 litter species that varied widely in traits and originated from four forest sites covering a large latitudinal gradient (subarctic to tropics) showed a consistent interspecific ranking of decomposition rates. At a global scale, variation in decomposition was driven by a small subset of litter traits (water saturation capacity and concentrations of magnesium and condensed tannins). These consistent findings, that were largely independent of the varying local decomposer communities, suggest that decomposer communities show little specialisation and high metabolic flexibility in processing plant litter, irrespective of litter origin. Our results provide strong support for using trait‐based approaches in modelling the global decomposition component of biosphere‐atmosphere carbon fluxes.
We explore empirical and theoretical evidence for the functional significance of plant-litter diversity and the extraordinary high diversity of decomposer organisms in the process of litter ...decomposition and the consequences for biogeochemical cycles. Potential mechanisms for the frequently observed litter-diversity effects on mass loss and nitrogen dynamics include fungi-driven nutrient transfer among litter species, inhibition or stimulation of microorganisms by specific litter compounds, and positive feedback of soil fauna due to greater habitat and food diversity. Theory predicts positive effects of microbial diversity that result from functional niche complementarity, but the few existing experiments provide conflicting results. Microbial succession with shifting enzymatic capabilities enhances decomposition, whereas antagonistic interactions among fungi that compete for similar resources slow litter decay. Soil-fauna diversity manipulations indicate that the number of trophic levels, species identity, and the presence of keystone species have a strong impact on decomposition, whereas the importance of diversity within functional groups is not clear at present. In conclusion, litter species and decomposer diversity can significantly influence carbon and nutrient turnover rates; however, no general or predictable pattern has emerged. Proposed mechanisms for diversity effects need confirmation and a link to functional traits for a comprehensive understanding of how biodiversity interacts with decomposition processes and the consequences of ongoing biodiversity loss for ecosystem functioning.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, INZLJ, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK, ZRSKP
Many experiments have shown that local biodiversity loss impairs the ability of ecosystems to maintain multiple ecosystem functions at high levels (multifunctionality). In contrast, the role of ...biodiversity in driving ecosystem multifunctionality at landscape scales remains unresolved. We used a comprehensive pan-European dataset, including 16 ecosystem functions measured in 209 forest plots across six European countries, and performed simulations to investigate how local plot-scale richness of tree species (α-diversity) and their turnover between plots (β-diversity) are related to landscape-scale multifunctionality. After accounting for variation in environmental conditions, we found that relationships between α-diversity and landscape-scale multifunctionality varied from positive to negative depending on the multifunctionality metric used. In contrast, when significant, relationships between β-diversity and landscape-scale multifunctionality were always positive, because a high spatial turnover in species composition was closely related to a high spatial turnover in functions that were supported at high levels. Our findings have major implications for forest management and indicate that biotic homogenization can have previously unrecognized and negative consequences for large-scale ecosystem multifunctionality.
Biodiversity experiments have identified both complementarity and selection as important drivers of the relationship between biodiversity and ecosystem functioning. However, their relative importance ...in above‐ and below‐ground ecosystem compartments of mature forests remains yet to be explored.
We adopted a trait‐based approach to partition biodiversity effects in above‐ and below‐ground complementarity and selection. This approach was based on canopy and root traits measured in single‐ and mixed‐species plots in mature forests across a European latitudinal gradient.
We assessed the relative importance of above‐ and below‐ground selection and complementarity in driving the relationship between tree species diversity and above‐ground wood production. We used the expected values (based on the values measured in monocultures) of leaf area index (LAI) and fine root biomass as proxies for above‐ and below‐ground selection, whereas canopy packing and rooting depth variability were used as proxies for above‐ and below‐ground complementarity.
Our results showed that tree species richness–wood production relationships were driven by above‐ and below‐ground complementarity (i.e. canopy packing and rooting depth variability), rather than selection. The proxies for selection were found to have a positive effect on wood production but were not affected by tree species richness.
We concluded that above‐ground‐ but also the largely neglected below‐ground complementarity drives biodiversity–productivity relationships in mature forests. Our findings suggest that choosing tree species with complementary above‐ and below‐ground traits should be considered in afforestation and forest management to promote tree diversity and productivity in European forests.
摘要
生物多样性实验将互补(complementarity)和选择(selection)视为生物多样性与生态系统功能之间关系的重要驱动因素。然而，两者在成熟林生态系统地上与地下部分的相对重要性仍待探索。
我们采用了基于功能性状的方法，将生物多样性效应分解为地上和地下互补与选择。该方法主要基于欧洲纬度梯度上在单一物种和混合物种成熟林所测得的冠层和根系功能性状。
我们评估了地上和地下选择与互补对树种多样性与地上木材产量之间关系的相对重要性。我们用叶面积指数(LAI)和细根生物量的期望值(基于单物种样方的观测值计算所得)来表征地上和地下选择，而用冠层堆积和根系深度异质性来表征地上和地下互补。
结果表明，树种丰富度与木材产量的关系是由地上和地下互补(即冠层堆积和根系深度异质性)驱动，而不是由选择驱动。同时发现，表征选择的功能性状(LAI和细根生物量的期望值)对木材生产有积极影响，但不受树种丰富度的影响。
本文的结论是，不仅地上互补，而且被忽视的地下互补也驱动了成熟林生物多样性与生产力的关系。这些发现表明，在造林和森林管理中应考虑选择具有地上和地下互补性状的树种以促进欧洲森林树木的多样性和生产力。
A free Plain Language Summary can be found within the Supporting Information of this article.
A free Plain Language Summary can be found within the Supporting Information of this article.
There is considerable evidence that biodiversity promotes multiple ecosystem functions (multifunctionality), thus ensuring the delivery of ecosystem services important for human well-being. However, ...the mechanisms underlying this relationship are poorly understood, especially in natural ecosystems. We develop a novel approach to partition biodiversity effects on multifunctionality into three mechanisms and apply this to European forest data. We show that throughout Europe, tree diversity is positively related with multifunctionality when moderate levels of functioning are required, but negatively when very high function levels are desired. For two well-known mechanisms, 'complementarity' and 'selection', we detect only minor effects on multifunctionality. Instead a third, so far overlooked mechanism, the 'jack-of-all-trades' effect, caused by the averaging of individual species effects on function, drives observed patterns. Simulations demonstrate that jack-of-all-trades effects occur whenever species effects on different functions are not perfectly correlated, meaning they may contribute to diversity-multifunctionality relationships in many of the world's ecosystems.
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