International audienceThe consequences of predicted climate change on ecosystem processes is difficult to evaluate, because biodiversity is also susceptible to change resulting in complex interactions on ecosystem functioning. With an experimental approach, we aimed to understand how plant community diversity (through different plant litter mixtures) and climate change (through decreased precipitation) may impact microbial abundance and diversity and affect C and N cycling in a Mediterranean shrubland. Along a natural plant diversity gradient, we manipulated the amount of precipitation and followed leaf litter decomposition during one year. We found that multi-species litter mixtures had higher microbial abundance, lower bacterial diversity and higher fungal diversity than predicted from single-species litter. In addition, C and N release increased with increasing litter species richness. Microbial abundance and diversity were positively, but weakly, correlated to the litter mixture effects on C and N release. Drier conditions increased microbial diversity but had no effect on microbial abundance. The net release of N from decomposing litter was lower with reduced precipitation irrespective of litter species richness and composition, while that of C was higher or lower depending on litter species composition. The relationships between microbial communities and litter mixture effects on C and N release were altered under drier conditions. Our data provide clear evidence that microbial decomposers and the processes they drive, respond to changing plant community diversity and composition in a Mediterranean shrubland. We highlighted the importance of Quercus coccifera that appears to be a key species in shaping microbial communities and driving synergistic effects on C and N release more than the three other shrub species. Our study also suggests that shifts in the plant community composition may have stronger impacts on litter decomposition and nutrient cycling than relatively subtle changes in precipitation as simulated in our study

BackgroundPlant biomass conversion for green chemistry and bio-energy is a current challenge for a modern sustainable bioeconomy. The complex polyaromatic lignin polymers in raw biomass feedstocks (i.e., agriculture and forestry by-products) are major obstacles for biomass conversions. White-rot fungi are wood decayers able to degrade all polymers from lignocellulosic biomass including cellulose, hemicelluloses, and lignin. The white-rot fungus Polyporus brumalis efficiently breaks down lignin and is regarded as having a high potential for the initial treatment of plant biomass in its conversion to bio-energy. Here, we describe the extraordinary ability of P. brumalis for lignin degradation using its enzymatic arsenal to break down wheat straw, a lignocellulosic substrate that is considered as a biomass feedstock worldwide.ResultsWe performed integrative multi-omics analyses by combining data from the fungal genome, transcriptomes, and secretomes. We found that the fungus possessed an unexpectedly large set of genes coding for Class II peroxidases involved in lignin degradation (19 genes) and GMC oxidoreductases/dehydrogenases involved in generating the hydrogen peroxide required for lignin peroxidase activity and promoting redox cycling of the fungal enzymes involved in oxidative cleavage of lignocellulose polymers (36 genes). The examination of interrelated multi-omics patterns revealed that eleven Class II Peroxidases were secreted by the fungus during fermentation and eight of them where tightly co-regulated with redox cycling enzymatic partners.ConclusionAs a peculiar feature of P. brumalis, we observed gene family extension, up-regulation and secretion of an abundant set of versatile peroxidases and manganese peroxidases, compared with other Polyporales species. The orchestrated secretion of an abundant set of these delignifying enzymes and redox cycling enzymatic partners could contribute to the delignification capabilities of the fungus. Our findings highlight the diversity of wood decay mechanisms present in Polyporales and the potentiality of further exploring this taxonomic order for enzymatic functions of biotechnological interest.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1198-5) contains supplementary material, which is available to authorized users.

Tree species diversity of forested ecosystems control the diversity of leaf litter inputs to the soil, with cascading effects on the microbial communities colonizing decomposing litter. However, the extent to which bacterial and fungal communities inhabiting the litter layer are affected by shifts in tree species diversity is not well understood. To investigate the role of litter species diversity, litter species identity and litter functional traits on bacterial and fungal communities of a typical Mediterranean oak forest, we set up a yearly field litterbag experiment that considered leaf litter mixtures of four abundant species: Quercus pubescens, Acer monspessulanum, Cotinus coggygria and Pinus halepensis. We found that both bacterial and fungal communities varied strongly during decomposition but showed distinct succession patterns. Both communities were also strongly influenced by litter species diversity, litter identity and litter functional traits. The intensity and the direction of these effects varied during decomposition. Litter diversity effects were mediated by litter species composition rather than litter species richness, highlighting the importance of litter species identity-and associated litter traits-as drivers of microbial communities. Both the "mass-ratio hypothesis", measured through the community weighted mean (CWM) litter traits, and the "niche complementarity hypothesis", measured through the functional dissimilarity (FD) of litter traits, contributed to litter diversity effects, with a greater relative importance of FD compared to CWM, and with an overall stronger impact on fungal than on bacterial communities. Interestingly, increasing FD was related to decreasing bacterial diversity, but increasing fungal diversity. Our findings provide clear evidence that any alteration of plant species diversity produces strong cascading effects on microbial communities inhabiting the litter layer in the studied Mediterranean oak forest.