Mountain ecosystems in drylands are generally constrained by phosphorus (P) availability, depending on the abundance and composition of soil inorganic and organic P (P i and P o ) fractions. However, shifts in P fractions and their edaphic drivers across vegetation types along elevational gradients in dryland mountain ecosystems remain poorly understood. Using topsoil (0–20 cm) samples collected from four primary vegetation types at different elevations in the Qilian Mountains of China’s drylands: grassland (2700–2800 m), spruce forest (2900–3000 m), subalpine shrubland (3400–3500 m), and alpine shrub-meadow (3600–3700 m), we investigated changes in different bioavailable P fractions, including labile P i (resin-P i + NaHCO 3 -P i ) and P o (NaHCO 3 -P o ), moderately labile P i (NaOH-P i ) and P o (NaOH-P o ), and relatively stable P i (HCl-P i ) and P o (HCl-P o ), and their relationships with soil biogeochemical properties (clay content, pH, alkaline phosphatase activity, exchangeable cations, and reactive Fe/Al oxides). We evaluated the individual and interactive effects of edaphic variables on P fractions using boosted regression trees model and path analysis. Soil P o fractions showed consistent changes across the sites, with their concentrations peaking in the alpine shrub-meadow and being lowest in the spruce forest, whereas P i fractions exhibited distinct shifting patterns with their maximum and minimum concentrations occurring in variable vegetation types. Edaphic variables explained most of the variation in P i (76–87%) and P o (65–81%) fractions, but they exhibited complex mechanisms governing the dynamics of P fractions. Notably, alkaline phosphatase activity negatively affected P o concentrations but positively influenced P i concentrations, whereas amorphous Fe/Al oxides negatively impacted labile P i but enhanced Fe/Al-associated P storage. Our results reveal contrasting distribution patterns of P i and P o fractions across vegetation types and highlight the crucial roles of soil biogeochemical drivers in regulating multi-pool P i and P o dynamics in mountain ecosystems.
Wang et al. (Sat,) studied this question.