Effect of Drying–Rewetting Alternation on Phosphorus Fractions in Restored Wetland

Wetlands frequently experience drying and rewetting (DRW) alternation, which intricately influences the physical, chemical, and biological processes within the soil matrix. The conversion of agricultural land into wetland ecosystems has raised significant concerns regarding the release of phosphorus. However, a significant knowledge gap persists in understanding the implications of this phenomenon for phosphorus transformation and release dynamics within soils situated in the freeze–thaw zone of Northeast China. To address this gap, we conducted a series of experiments involving the simulation of varying intensities and frequencies of DRW alternation using soil column samples collected from restored wetlands. This study evaluated phosphorus fractions with different levels of mobility and availability using methods based on standardized chemical extraction. We subsequently analyzed the impacts of these alterations on phosphorus fractions from the perspectives of soil chemical properties and microbial community changes. DRW events were found to facilitate the conversion of labile inorganic phosphorus into organic phosphorus fractions, driving the transformation of mobile phosphorus into potentially mobile fractions. Moderate drought events showed a significant increase in soil bacterial diversity and abundance, while both normal and extreme drought events caused a decrease in bacterial diversity. Moreover, DRW treatment increased the relative abundance of Proteobacteria and decreased the relative abundance of Chloroflexi. Redundancy analysis identified organic carbon and bacterial diversity as key drivers influencing phosphorus fractions. Overall, this study contributes to our understanding of the intricate relationships among soil characteristics, microbial ecosystems, and the complex behavior of phosphorus under various DRW regimes in restored wetlands.