Drought and vegetation restoration patterns shape soil enzyme activity and nutrient limitation dynamics in the loess...

Appropriate vegetation restoration measures are beneficial to ecosystem restoration and nutrient retention in ecologically fragile areas. However, the high water consumption of planted forests and the increasing frequency of drought events may reshape or complicate this ecological process. The effects of forest types and drought stress on nutrient limitation remain unclear. In this study, we selected five different vegetation restoration types on the Loess Plateau, China, and applied three drought levels to assess their effects on extracellular enzyme activity, soil microbial biomass, and soil nutrient limitations.We measured the activities of carbon-, nitrogen-, and phosphorus-acquiring enzymes and investigated the relationships among enzyme activity, microbial biomass, and nutrient limitations under drought conditions. Our results showed that vegetation types and drought significantly influenced soil enzymatic activity and stoichiometry. Mixed forests demonstrated higher enzyme activity and nutrient content compared to pure forests, indicating greater resilience under drought conditions. Short-term drought significantly reduced soil enzyme activity and microbial biomass, whereas mild drought stimulated enzyme activity, and moderate drought promoted microbial biomass. Drought markedly decreased microbial carbon and nitrogen content but increased the microbial carbon-to-nitrogen ratio. Furthermore, drought enhanced the correlation between microbial biomass carbon and carbon-acquiring enzymes, but there was no correlation between microbial biomass nitrogen and nitrogen-acquiring enzymes under drought. All vegetation types exhibited nitrogen limitation, and a negative correlation was observed between nitrogen and carbon limitations under drought conditions. Drought significantly exacerbated nitrogen limitation, while its impact on carbon limitation varied with drought severity and vegetation type. Overall, plant communities exhibited distinct nutrient acquisition strategies under drought stress, resulting in complex changes in soil enzyme activities and microbial biomass. This study advances our understanding of microbial nutrient limitations and enzymatic activities under varying vegetation restoration patterns and drought conditions, providing critical insights for enhancing soil resilience and nutrient cycling under climate change.