Differential impacts of moisture fluctuation on dissolved organic matter under different water availability by...

Changes in turnover of dissolved organic matter (DOM) influence the stability and storage of soil carbon under global warming. The understanding of its responses to the climate extremes like drought has advanced in recent years. Nevertheless, how global warming-induced moisture fluctuation affects the ecological process of DOM, and the underlying mechanisms of this microbe-driven C-cycling remain less known. Our study established a microcosm system to experimentally test the differential impacts of moisture fluctuation under different water availability conditions by regulating the precipitation intensity, precipitation frequency, and evaporation intensity. The results from the 16-week incubation showed that intense moisture fluctuation promoted DOM accumulation with distinct mechanisms. The increased DOM content at drought was likely due to the abiotic processes associated with the weakening in bacterial activity and network complexity, while it was mainly contributed by the enhancement of the activity and metabolism of bacteria at wet condition. Although highly fluctuated moisture substantially inhibited microbial respiration and simplified the network topological structure, such detrimental influence could be compensated when water availability condition was favorable for the bacterial growth. Collectively, these findings demonstrated that the ecological process of DOM was regulated by the interactive effects of average and fluctuation of soil moisture condition, highlighting the importance of considering fluctuation pattern in understanding the microbe-driven DOM turnover in the context of climate change.