Variations in soil phosphorus biogeochemistry across six vegetation types along an altitudinal gradient in SW China

- Soil P biogeochemistry across 7 altitudes with 6 vegetation types was studied.
- The TP stock was higher in 3838-4235 m than that in 2032-3614 m.
- Labile P showed a parabolic trend with an altitude that was inverse with HCl-Pi.
- Variation of labile P along the gradient was mainly impacted by soil pH and vegetation type.
- Temperature is an additional factor affecting change of labile P in 3060-4235 m.

The impacts and relative importance of temperature, precipitation, lithology, soil properties, vegetation type and microbial activity on soil P biogeochemistry along altitudinal gradients are poorly understood. Our aim is to reveal the variations and main driving factors governing soil P forms across six different vegetation types along an altitudinal gradient (2032-4235 m asl) on Mt. Gongga, southwest China. Soil P forms were measured using a sequential fractionation technique. The results showed that the spatial distributions of total P and organic P clearly exhibited altitudinal variations along the gradient. The total P stocks in the 3838-4235 m zones were significantly higher than those in the 2032-3614 m zones. This pattern is likely influenced by climate, soil erosion, total P content in the parent material and vegetation type. Unlike the total P stock, the concentrations and stocks of available P in the surface soils showed a parabolic pattern with altitude, with maximums at the 3060 m site and minimums at the lowest site. The Ca-Pi concentrations (extracted by 1 M HCl solutions) displayed a spatial pattern opposite to that of the available P. The NaOH-Pi concentrations changed little with altitude and accounted for a small part of the total P. The Ca-Pi represented the largest part of the total P at the 2032 m site and in the alpine zones, whereas the organic P contributed the largest portion of total P in the sub-alpine zones. A redundancy analysis showed that the general spatial pattern of all the P forms was mainly related to soil pH, vegetation and soil organic matter. In particular, the soil pH, which was mainly controlled by vegetation type and precipitation, significantly influenced the altitudinal pattern of Ca-Pi. The effect of soil pH, perhaps coupled with the amount of P returned by litter production, is a crucial factor in the parabolic pattern of available P between 2032 and 4235 m asl. Furthermore, in the 3060-4235 m zone, temperature becomes an additional important factor governing the pattern of available P due to its influence on litter decomposition rates. These results emphasize the central role of vegetation in regulating soil P biogeochemistry along the altitudinal gradient by affecting soil properties and litter production.