Plant litter chemistry and associated changes in microbial decomposition under drought

Abstract

Drought has consequences for microbial decomposition rates, including indirect effects through changes in plant litter chemistry. Here we studied the impact of a decade-long drought on plant litter chemistry and microbial decomposition traits in a semi-arid ecosystem during an 18-month litter bag experiment. We investigated litter sourced from four conditions: grass and shrub vegetation under ambient and reduced precipitation. We hypothesized that litter chemistry drives microbial decomposition capabilities and enzyme activity, either due to vegetation differences or drought effects on litter chemistry. Fourier Transform Infrared Spectroscopy was used to characterize litter chemistry; we found that carbohydrate-rich grass litter decomposed faster than more recalcitrant shrub litter which was richer in lignin and lipids. There were significant changes in litter chemistry under drought but no increase in lignin fraction suggesting that drought does not make litter more recalcitrant. Metagenomics-derived decomposition genes and extracellular enzyme activity were higher in grass litter; patterns related to differences in substrate supply. Genes linked to lignin depolymerization decreased in abundance under drought. However, most decomposition genes and enzyme activities were not significantly affected by drought thereby maintaining decomposition rates. Microbial community succession with higher abundance of fungi at early and bacteria at later stages of decomposition corresponded with genes for fungal and bacterial necromass recycling along with protein accumulation over time. We demonstrate minimal litter chemistry-mediated effects of drought but show significant changes in community composition and their decomposition capabilities over time highlighting that complex microbial-chemical interactions under climate change can influence ecosystem-scale processes. ImportanceClimate change is causing more severe and frequent droughts in semi-arid ecosystems, affecting soil microbes breaking down plant litter. Our research focusses on understanding the less studied pathway of drought impact on microbes via changes in plant litter chemistry. Drought can alter the plant litter chemistry, by changing the composition and physiology of plants, which can alter microbial decomposition and ecosystem-level carbon cycling. We investigated litter decomposition traits of microbial communities in grass and shrub litter under long-term drought. There were significant changes in litter chemistry under drought but no increase in lignin fraction. Despite this, microbial communities maintained their decomposition capabilities under drought highlighting ability of microbes to adapt and continue functioning. We also demonstrate unique microbial community succession patterns and dead biomass recycling which can have implications for carbon cycling rates in the ecosystem. This study sheds light on the complex microbial interactions that affect ecosystem functioning under climate change.