How do climate warming affect soil aggregate stability and aggregate-associated phosphorus storage under natural restoration?

The responses of soil aggregation and aggregate-associated phosphorus (P) fractions under natural restoration to climate warming remain unclear. Here, we conducted an eight-year mesocosm experiment wherein farmland soil from a colder site was transplanted to a warmer site to simulate climate warming and established continuous soybean cultivation and natural restoration treatments at each site. We investigated soil aggregate stability and the associated P fractions and soil properties under two land-use systems in a warming climate. Our results revealed that natural restoration significantly increased macroaggregates and macroaggregate-associated NaHCO₃-Pi, NaOH-Po, and TP, but warming impeded the increases of these P fractions without changing soil aggregation. Although TP within microaggregates and the silt and clay fractions remained consistent across treatments, warming resulted in higher NaHCO₃-Pi concentrations in both fractions and lower NaHCO₃-Po and NaOH-Po within microaggregates in restored land. Bacterial community and alkaline phosphatase activity may be responsible for organic P mineralization within microaggregates. The enrichment of NaHCO₃-Pi in smaller-sized aggregates and non-aggregate particles with warming likely increased the risk for P loss. Fungal and bacterial phospholipid fatty acid explained the most variation in the P fractions within macroaggregates and microaggregates, respectively, suggesting that biological processes are involved in determining P distribution. Our study indicates that the distribution of P fractions in differently sized aggregates during natural restoration can be significantly influenced by warming and highlights that incorporating the responses of soil microorganisms and enzymes will improve our understanding of the P cycling in a warming climate.