The alleviation of phosphorus (P) limitation by increasing carbon (C) input is an effective strategy for improving crop production and P uptake efficiency. However, the effects of straw returning on soil microbial biomass P (MBP) turnover and P fractions in paddy-upland rotation remain poorly understood. Soil MBP turnover involves the mineralization and immobilization of organic P (Po), potentially altering P fractions and reducing the risk of P loss. The effects of straw returning on soil MBP turnover, P fractions and crop P utilization during the rice-oilseed rape rotation were evaluated in two field experiments with different soil Po levels. The treatments included no P fertilizer (-P), P fertilizer (+P) and P fertilizer plus straw returning (+P + S). The crop P uptake and cumulative P utilization efficiency were increased by straw returning. Straw addition promoted microbial biomass, decreased the MBC:MBP ratio in Po-high soil, increased the MBC:MBP ratio in Po-low soil, and increased the MBP turnover rates and fluxes in both soils. According to structural equation modeling (SEM), soil MBC and MBP had significant effects on crop P uptake directly or via P fractions. In Po-high soil, straw addition increased inorganic P (Pi) (NaHCO₃ and NaOH) and decreased Po content by increasing the MBP turnover, while the Po-low soil mainly increased Po content. Among multiple observed variables, MBP was the most important driving factor controlling P uptake in Po-high soil, while MBC and NaOH-Pi were the best driving factors in Po-low soil. Additionally, the soil MBC, MBP and MBC:MBP ratios were higher in the oilseed rape season than in the rice season. Consequently, straw returning improves soil P availability by increasing MBP turnover, which is beneficial for improving P utilization.

通过增加碳（C）输入来缓解磷（P）限制是提高作物产量和磷吸收效率的有效策略。然而，秸秆还田对稻田-旱地轮作中土壤微生物量磷（MBP）周转和磷分数的影响仍然知之甚少。土壤 MBP 周转涉及有机磷 (Po) 的矿化和固定化，可能会改变磷的比例并降低磷损失的风险。在两个不同土壤磷水平的田间试验中，评估了稻草还田对水稻-油菜轮作过程中土壤 MBP 周转率、磷组分和作物磷利用的影响。处理包括无磷肥（-P）、磷肥（+P）和磷肥加秸秆还田（+P+S）。秸秆还田提高了作物对磷的吸收和累积磷利用效率。秸秆添加促进了微生物生物量，降低了 Po-high 土壤的 MBC:MBP 比，增加了 Po-low 土壤的 MBC:MBP 比，并增加了两种土壤的 MBP 周转率和通量。根据结构方程模型 (SEM)，土壤 MBC 和 MBP 直接或通过 P 组分对作物 P 吸收具有显着影响。在 Po 高的土壤中，秸秆添加增加了无机 P (Pi) (NaHCO₃和 NaOH），并通过增加 MBP 周转率降低 Po 含量，而 Po 低土壤主要增加 Po 含量。在多个观测变量中，MBP是控制Po-高土壤P吸收的最重要驱动因素，而MBC和NaOH-Pi是Po-低土壤最好的驱动因素。此外，油菜季节土壤 MBC、MBP 和 MBC:MBP 比值高于水稻季节。因此，秸秆还田通过增加 MBP 周转率来提高土壤磷的有效性，这有利于提高磷的利用率。