Long-term droughts can significantly reduce forest productivity due to water deficiency and associated changes in the availability of soil nutrients. Phosphorus (P) is a critical but limited element in subtropical forest ecosystems. However, how soil P availability responds to drought and the underlying mechanisms in subtropical forests remain poorly understood. In this study, we investigated the effects of drought treatment on soil P fractions, soil available N, microbial biomass N (MBN), microbial biomass P (MBP), soil microbial phospholipid fatty acids (PLFAs), enzyme activities, fine root biomass (FRB), and fine root biomass P (FRBP) in a subtropical Castanopsis carlesii forest after 7.5 years of throughfall exclusion. The results showed that throughfall exclusion significantly decreased resin extractable P (Resin-P) and total extractable organic P, suggesting that drought induced a reduction in soil available P and organic P. Meanwhile, Resin-P was positively correlated to total extractable organic P but not with NaHCO₃ extractable P (NaHCO₃-P) and total extractable inorganic P, which indicated that the decline of available P in soil was mainly associated with the reduction of organic P. In addition, soil microbial biomass, MBN, MBP, FRB, and FRBP were reduced under the throughfall exclusion treatment. The MBP and FRBP were positively correlated with Resin-P and total extractable organic P. These results implied that the reductions of MBP and FRBP primarily contributed to the declines of soluble P and organic P. Such information is essential for understanding the roles of microbes and plant roots on soil P cycle in subtropical forests under drought.

由于缺水和土壤养分有效性的相关变化，长期干旱会显着降低森林生产力。磷（P）是亚热带森林生态系统中一种关键但有限的元素。然而，土壤磷的有效性如何响应干旱以及亚热带森林的潜在机制仍然知之甚少。在本研究中，我们研究了干旱处理对土壤 P 组分、土壤有效 N、微生物生物量 N (MBN)、微生物生物量 P (MBP)、土壤微生物磷脂脂肪酸 (PLFAs)、酶活性、细根生物量 ( FRB) 和亚热带卡氏栲中的细根生物量 P (FRBP)森林经过 7.5 年的通透排除。结果表明，透水排除显着降低了树脂可提取磷（Resin-P）和可提取有机磷总量，表明干旱导致土壤有效磷和有机磷减少。同时，树脂磷与可提取有机磷总量呈正相关，但不与 NaHCO ₃可萃取 P (NaHCO ₃-P) 和总可提取无机磷，表明土壤有效磷的下降主要与有机磷的减少有关。此外，在穿透排除下，土壤微生物生物量、MBN、MBP、FRB 和 FRBP 减少治疗。MBP 和 FRBP 与 Resin-P 和总可提取有机 P 呈正相关。这些结果表明 MBP 和 FRBP 的减少主要导致可溶性 P 和有机 P 的下降。这些信息对于理解微生物和有机磷的作用至关重要。干旱条件下亚热带森林植物根系对土壤磷循环的影响。