Altitudinal and seasonal variation in soil phosphorus fractions in Moso bamboo forests

Abstract Soil phosphorus (P) availability is pivotal for plant growth and ecosystem productivity, yet the distribution and regulation of soil P fractions across environmental gradients in subtropical bamboo forests remain poorly constrained. We investigated Moso bamboo forests across five altitudes in subtropical eastern China, collecting soil samples in both summer and winter to evaluate soil physico-chemical and microbial properties. Soil P fractions were determined using the Hedley sequential extraction procedure and classified into labile P (Resin-P, NaHCO3-Pi/Po), moderately labile P (NaOH-Pi/Po), and stable P (NaOHus-Pi/Po, HCl-P, Residual-P). Soil P fractions were dominated by NaOH-P, which accounted for 37.2–47.0% of total P. Most P fractions (NaOH-Pi/Po, NaOHus-Pi/Po, NaHCO3-Po, HCl-P, and Residual-P) exhibited non-linear (parabolic) relationships with altitude, whereas NaHCO3-Pi increased linearly with altitude during summer. Altitude exerted a stronger influence on most soil P fractions than season, with the exceptions of Resin-P and HCl-P. Microbial biomass nitrogen (MBN) in winter was approximately 32.3% higher than in summer, suggesting that soil microbes may accumulate more nitrogen under low temperatures to compensate for reduced metabolic activity. Soil moisture (SM) was the primary driver of P fractions variation in summer, likely enhancing P mobility, whereas microbial biomass P (MBP) became the dominant regulator in winter, potentially facilitating P turnover and mitigating sorption by Fe and Al oxides. These findings highlight the intricate coupling of hydrological and microbial processes in modulating soil P availability. Managing soil moisture and microbial activity may therefore offer practical strategies to sustain productivity in intensively managed subtropical Moso bamboo forests.