Land-use-driven changes in functional profiles of microbial lipid metabolism affect soil water repellency

Soil water repellency (WR) is an important hydrological function in the terrestrial water cycle as it prevents water from penetrating into the soil and exacerbating soil erosion. Vegetation restoration may greatly affect WR by increasing soil organic carbon (OC) storage and altering microbial community composition in response to environmental stressors in the loess hilly areas of China. Yet, the regulating mechanisms of WR by changes in microbial functional profiles across land use types in these regions are poorly characterized. In this work, solidstate13C nuclear magnetic resonance (NMR) spectroscopy and shotgun metagenomics sequencing were applied to systematically assess the effects of land use types on the OC fractions, soil bacterial and fungal community composition, as well as microbial functional profiles. We found that artificial evergreen coniferous forestland caused more severe WR and increased the complexity of fungal networks. Besides, the artificial evergreen coniferous forestland had larger impacts on labile OC fractions, microbial communities,and lipid metabolic pathways in topsoil compared to other land use types. What's more, keystone genera (e.g., Conexibacter, Streptomyces, and Sphaerobolus) and functional genes (ACAT, atoB, ACSL, fadD, ACADM, acd, paaF, echA, and FAS2) were driven by soil properties that contributed significantly to WR. Collectively, our results indicate that topsoil OC fractions interact with keystone taxa to influence WR by regulating functional genes in lipid metabolic pathways. These findings greatly boost our understanding of assessing the SWR risk against the backdrop of climate change and lay a theoretical foundation for formulating rational vegetation restoration management strategies based on variations in SWR of forest (grassland) ecosystems on the Chinese Loess Plateau.