The distribution, effectiveness and environmental threshold of soil aggregate phosphorus fractions in the sub‐alpine region of Southwest China

Abstract This article is a study of total phosphorus (TP), available phosphorus (AP) and phosphorus (P) fractions of soil aggregates along an altitude gradient in the sub‐alpine region of Southwest China. We conclude that soil aggregate TP and AP contents are higher at 3980 m and 3347 m; there are no significant differences in soil aggregate TP at any altitude ( p > 0.05); the AP and phosphorus activation coefficient (PAC) are higher in 0.25–0.5 mm aggregate. Soil aggregates TPi > TPo at 3009 m and TPo > TPi at 3347, 3654 and 3980 m. Using multiple stepwise regression analysis, we conclude that NaOH‐Pi is the key fraction of AP supply, NaHCO 3 ‐Pi and NaOH‐Pi are important fractions of CaCl 2 ‐P. Through piecewise linear fitting of soil aggregate AP and CaCl 2 ‐P, the soil P environmental threshold obtained is 27.766 mg kg −1 in this region. Also we got <0.25 mm, 0.25–0.5 mm aggregates at 3980 m which have high soil P loss risk. Our study fills in gap about the distribution of P fraction in aggregates and effects of soil P fraction for AP and CaCl 2 ‐P in high‐altitude areas. Our study provides a reference and scientific basis for understanding the soil aggregate P storage capacity and the biological effectiveness of P fractions at high altitudes. Our study on the P environmental threshold provides a reference for soil P storage capacity. Our study provides a reference value for the soil P loss risk management, and sustainable development of soil ecosystems in the sub‐alpine region of Southwest China.