Moisture fluctuations: An important but overlooked factor in the carbon cycle.

Global warming has intensified extreme weather events and current studies on soil carbon dynamics have predominantly focused on the stress of average moisture, while the significance of moisture fluctuation has been largely ignored. To fill this knowledge gap, we systematically explored the impact of multi-dimensional changes in soil moisture on different labile carbon pools through a meta-analysis using 1665 data points based on soils collected globally. By evaluating the interactive effects of different levels of average, fluctuation, and changing frequency of soil moisture during incubation experiments, our results showed that the dynamics of CO emissions and microbial biomass carbon (MBC) were mainly influenced by soil moisture level, while the change of dissolved organic matter (DOM) was more strongly associated with moisture fluctuation. Besides, more frequent and extended duration of wet-dry cycling influenced the CO emission as well as the mineralization of active soil carbon pools like MBC and DOM. Furthermore, the word cloud analysis identified that biological processes like microbial activity and community composition were the key drivers in mediating the effects of moisture variability on carbon storage and turnover. These findings indicate that both static and dynamic moisture conditions are critical to deepen our understanding in the impact of varying moisture on soil carbon storage, emphasizing the necessity of incorporating multi-dimensional moisture changes in assessing the responses of C-cycling in the context of climate change.