Drying-rewetting cycles reduce bacterial diversity and carbon loss in soil on the Loess Plateau of China

With global climate change, soil drying-rewetting (DRW) events have intensified and occurred frequently on the Loess Plateau of China. However, the extent to which the DRW cycles with different wetting intensities and cycle numbers alter microbial community and respiration is barely understood. Here, indoor DRW one and four cycles treatments were implemented on soil samples obtained from the Loess Plateau, involving increase of soil moisture from 10% water-holding capacity (WHC) to 60% and 90% WHC (i.e., 10%–60% and 10%–90% WHC, respectively). Constant soil moistures of 10%, 60%, and 90% WHC were used as the controls. The results showed that bacterial diversity and richness decreased and those of fungi remained unchanged under DRW treatments compared to the controls. Under all moisture levels, Actinobacteriota and Ascomycota were the most dominant bacterial and fungal phyla, respectively. The bacterial network was more complex than that of fungi, indicating that bacteria had a greater potential for interaction and niche sharing under DRW treatments. The pulse of respiration rate declined as the DRW cycle increased under 10%–60% WHC, but remained similar for different cycles under 10%–90% WHC. Moreover, the DRW treatments reduced the overall carbon loss, and the direct carbon release under 10%–60% WHC was larger than that under 10%–90% WHC. The cumulative CO₂ emissions after four DRW cycles were significantly positively correlated with microbial biomass carbon and negatively correlated with fungal richness (Chao 1).