Elevational variation in soil phosphorus pools and controlling factors in alpine areas of Southwest China

As an important life element in the Earth’s ecosystem, soil phosphorus (P) is of great significance to stability and sustainable development of terrestrial ecosystems. However, seasonal variations in different soil P pools and their regulatory mechanisms along elevations are not fully understood. Here, we investigated seasonal variations in soil P pools including total P (TP), available P (AP), inorganic P (IP), organic P (OP), labile P, moderately labile P, and stable P in topsoil (0–15 cm) along different elevations (2600–3900 m) in the Yulong Snow Mountain. The associated drivers including leaf nutrient contents, soil properties, micro-climate, and microbial parameters were also examined. We found that all soil P fractions reached a maximum at mid-elevations (2,900 m and 3,200 m), possibly due to the more active microorganisms and suitable soil climatic conditions for advancing P weathering. Meanwhile, soil AP pool was also observed to be tightly related to the leaf P content along elevations. Unexpectedly, most soil P pools did not show seasonal changes, except for AP showing significantly higher level in the wet season than in the dry season, owing to the high temperature and microbial activity for promoting P release in the wet season. Consequently, we found that microbial P, acid phosphatase and dissolved organic carbon had a stronger influence on different P pools than other soil factors. Moreover, there was a strong interaction of labile P and moderately labile P with soil environments (i.e. soil moisture, temperature, dissolved organic carbon). Collectively, our results revealed the elevational shifts in soil P pools and potential mechanisms in Yulong Mountain, and provided an important theoretical basis for soil P dynamics in response to environments in mountain ecosystems.