Environmental versus litter traits as drivers of microbial decomposer functions

Plant litter decomposition is a key ecosystem process with significant implications for global carbon cycling, soil fertility and plant productivity. Given that microbial decomposers are the main players in the decomposition process, it is surprising how little is known about their functional diversity in different habitats or their ability to respond to environmental changes. To fill this knowledge gap, we conducted a litterbag decomposition experiment along a pronounced climate and vegetation gradient in the Chilean Coastal Cordillera (26{degrees}S to 38{degrees}S), ranging from hyper-arid to temperate, using mixtures of four plant species, native to the respective ecosystems. We analyzed potential decomposition functions of bacterial and fungal litter communities along with their biotic (litter traits) and abiotic (meteorological conditions and soil properties) environments, to determine the relative importance of these environmental factors for microbial community functioning. We also tested the impact of the functional diversity of the decomposer communities (i.e., the diversity of decomposition related functions) on litter mass loss. Functional composition was related most strongly to the temporal variation of precipitation and radiation, explaining about 19 % and 6 % of variation in bacteria and fungi, respectively. In contrast, functional diversity was quite strongly related to litter chemical traits (C:N, C:P, tannins, phenols). Litter mass loss after six months of decomposition was not correlated to the functional diversity of decomposer communities but increased with the presence of habitat generalists like Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes. Taken together, these results highlight i) the interplay between abiotic factors and chemical litter traits on litter microbial functions and functional diversity and ii) the importance of microbial generalists for litter decomposition across different ecosystems. These results enhance our ability to predict changes in microbial decomposer communities and litter decomposition under future climate-change scenarios.