Earthworms mitigate drought effects on microbial decomposition of straw under varying microplastic conditions.

Microplastic pollution and drought stress potentially threaten soil functions (e.g., straw decomposition) in semi-arid agroecosystems of the Loess Plateau. large decomposers (e.g., earthworms) can promote straw decomposition by modulating soil physico-chemical properties and microbial communities. However, whether, how, and to what extent earthworms can mitigate these negative effects. Here, we conducted a microcosm experiment to test the effects of microplastic pollution (no microplastic addition vs. biodegradable microplastic vs. non-degradable microplastic), and drought stress (ambient vs. drought) on microbial decomposition of straw in the presence vs. absence of earthworms. We found that both biodegradable and non-degradable microplastics enhanced microbial decomposition of straw by 11 % and 29 %, respectively, by boosting microbial diversity and total biomass. Drought, conversely, reduced microbial decomposition by 30 %. Notably, earthworms mitigated drought effects by promoting microbial decomposition by 22 % through increasing soil carbon and nutrient availability, as well as microbial biodiversity and biomass. Overall, these findings suggest that large soil decomposers can substantially alleviate the detrimental effects of global changes on ecosystem functions by enhancing the community complexity of small detritivores.