Shifting from biotic to abiotic drivers of urban microbial multifunctionality under drought and rehydration

Climate change has intensified the frequency and severity of urban droughts, exposing urban green spaces to abrupt and extreme water shortage that disrupts plant-microbe interactions and microbial multifunctionality. Understanding how rhizosphere and phyllosphere microbial communities respond to drought and how these shifts influence urban microbial functions is crucial for developing strategies to enhance the resilience of urban ecosystems under climate change. In this study, we conducted microcosm experiments simulating four drought intensities, integrating omics technologies with soil enzyme stoichiometry to investigate the effects of drought on microbial communities associated with Zoysia japonica (Steud) and urban microbial multifunctionality. Our results demonstrate that drought intensities significantly altered the compositions of bacterial and fungal communities in both the rhizosphere and phyllosphere. Moreover, drought enhanced microbial multifunctionality by significantly affecting 21 microbial functional potentials, including carbon fixation and denitrification. Although urban microbial multifunctionality largely returned to the control level after rehydration, five functions remained altered, including phyllosphere organic nitrogen mineralization and soil polyphenol oxidase activity. Biotic factors, particularly rhizosphere bacteria and fungi, directly influenced microbial multifunctionality during drought, whereas abiotic factors, such as electrical conductivity, dissolved organic carbon, and ammonium-nitrogen (NH₄⁺-N), had indirect effects. After rehydration, abiotic factors, especially pH and NH₄⁺-N, emerged as the main direct drivers. These findings underscore a shift from biotic to abiotic regulation of urban microbial multi-functionality across drought and rehydration, emphasizing the vital role of microbial communities in ecosystem resilience and the need to consider both biotic and abiotic factors in urban drought management.