Professor University of California, Irvine Irvine, CA, United States
Abstract: Microbial-driven decomposition is a fundamental process in global biogeochemical cycles. Climate change-induced drought is known to affect decomposition, yet understanding and predicting the implications of microbial processes on decomposition remains a challenge. We hypothesized that drought imposes constraints on the metabolism of decomposers such that increased investment in stress tolerance traits reduces community growth yield and decomposition rates. In situ decomposition was monitored over 18-months in Mediterranean grass and shrub ecosystems following a decade-long drought using litter bags placed on soil surface. Patterns in species- and community-level genomic and phenotypic traits for drought stress tolerance, resource acquisition and growth yield were linked to litter chemistry and mass loss. Using metagenomics-assembled genomes, we demonstrate species-level drought stress tolerance mechanisms in bacteria and fungi that were linked to osmolytes, membrane transporters and iron acquisition. These adaptations increased microbial fitness such that decomposition genes and enzyme activities were not negatively affected by drought. Consequently, emergent community-level biomass, respiratory quotient and litter mass were similar across precipitation treatments in both ecosystems. However, drought changed grass litter chemistry which impacted resource acquisition traits to some extent. We conclude that community shifts in response to drought are linked not only to selective pressures of water-stress but also to substrate changes due to shifts in plant community, the latter being more consequential to litter decomposition. We thus demonstrate how individual-level physiology and the resulting trait trade-offs – or the lack of – structure species distribution, and determine the community response to drought and consequences for decomposition.
