Soil animals alter plant litter diversity effects on decomposition

Abstract

Most of the terrestrial net primary production enters the decomposer system as dead organic matter, and the subsequent recycling of C and nutrients are key processes for the functioning of ecosystems and the delivery of ecosystem goods and services. Although climatic and substrate quality controls are reasonably well understood, the functional role of biodiversity for biogeochemical cycles remains elusive. Here we ask how altering litter species diversity affects species-specific decomposition rates and whether large litter-feeding soil animals control the litter diversity-function relationship in a temperate forest ecosystem. We found that decomposition of a given litter species changed greatly in the presence of litters from other cooccurring species despite unaltered climatic conditions and litter chemistry. Most importantly, soil fauna determined the magnitude and direction of litter diversity effects. Our data show that litter species richness and soil fauna interactively determine rates of decomposition in a temperate forest, suggesting a combination of bottom-up and top-down controls of litter diversity effects on ecosystem C and nutrient cycling. These results provide evidence that, in ecosystems supporting a well developed soil macrofauna community, animal activity plays a fundamental role for altered decomposition in response to changing litter diversity, which in turn has important implications for biogeochemical cycles and the long-term functioning of ecosystems with ongoing biodiversity loss.biodiversity ͉ soil fauna ͉ temperate forest ecosystem P lants interact with ecosystem C and nutrient turnover in various ways (1, 2), but the importance of plant species diversity for these processes is not well understood. Living plant diversity can influence decomposition and nutrient dynamics through changes in microclimatic conditions (1, 3), complementary nutrient use (4, 5), and rhizosphere processes. In addition, the amount and quality of plant litter input have a strong impact on C and nutrient cycling (6-8). This litter effect depends on the relative contribution of different species and their characteristic litter traits to the overall community litter pool. There is clear evidence suggesting that observed rates of community litter mass loss and nutrient mineralization may deviate substantially from those expected from single-litter-species decomposition of component species because of nonadditive interactions among litter species (3, 9-13).We lack a mechanistic understanding of litter species interactions, and the variable results, ranging from clearly negative to strongly positive litter mixing effects, on decomposition are difficult to explain (11-13). Recent theory, and the rare attempts to perform experimental tests of specific mechanisms, have concentrated on bottom-up controls of distinct litter chemistries through nutrient translocation among litter species, or inhibiting compounds, and the results have been conflicting (10-16). Besides potential bottom-up control on litter species interaction...

C, N and P fertilization in an Amazonian rainforest supports stoichiometric dissimilarity as a driver of litter diversity effects on decomposition

“…R. Soc. B 281: 20141682 mixture decomposition has rarely been considered in previous studies, but the few extra-tropical studies specifically testing for soil fauna effects found that non-additive effects on litter mixture decomposition were mostly attributed to the presence of fauna [36][37][38][39][40]. Fauna could reinforce the litter mixtures effects directly through higher litter consumption in mixtures (owing to complementary uptake of resources from a mixed diet [36] and/or as a result of diluted inhibitory compounds [41]) and/or indirectly by altering the microbial decomposer activity.…”

Effects of mixture of branch order-based roots and nitrogen addition on root decay in a subtropical pine plantation

“…Although this mesh size may successfully avoid the physical loss of lower-order roots, it actually impedes the access of soil fauna into litterbags. Soil fauna plays an important role in litter decomposition and determines the magnitude and direction of litter diversity effects (Hättenschwiler and Gasser 2005). Hence, the lack of involvement of soil fauna may, to some extent, affect the pattern of the mixing effect.…”

Biodiversity and Ecosystem Functioning: a Conceptual Model of Leaf Litter Decomposition

“…On the other hand, the presence of some secondary plant metabolites, such as polyphenols, may decrease, revert, or even compensate synergistic mechanisms that would be occurring simultaneously. This effect would decrease the decomposition rate of litter mixture, when compared to the sum of decomposition rates observed in each of the species composing the mixture, causing the antagonistic effect [51,59]. Thus, plant diversity that composes the litter mixture would not always have the expected positive effect on decomposition.…”

“…These organisms remove, mix, break and digest the organic matter, metabolizing litter constituents, mineralizing and making nutrients available to plants [51]. Even though all components of the edaphic biota may perform important roles on litter decomposition, the main decomposing agents are fungi and bacteria, being responsible by nutrient mineralization.…”

“…Leaves with certain physical characteristics, such as lower hardness and lignin content, are correlated to higher decomposition rates [55]. Chemical aspects, such as higher carbon and nitrogen concentrations, are frequently correlated to higher decomposition rates [26,50,55,56], even though this pattern is not fully established [51]. According to our flowchart, there would be a positive relationship between environmental heterogeneity and the possibility of the litter mixture being explored Biodiversity -The Dynamic Balance of the Planetby different decomposer species, which possess distinct nutritional needs, or different abilities to exploit resources originated from a varied plant species.…”