Low molecular weight organic acids regulate soil phosphorus availability in the soils of subalpine forests, eastern Tibetan Plateau

Abstract The availability of phosphorus (P) in soils is an essential limiting factor for the development of terrestrial ecosystems; however, how root exudates affect the availability of soil P in subalpine forests remains unclear. The low molecular weight organic acids (LMWOAs) were analyzed in bulk and rhizosphere soils of Abie fabri dominated forests across four altitudes (2800–3500 m) on Gongga Mountain, eastern Tibetan Plateau, to delineate the effects of LMWOAs on the availability of soil P in response to the rhizosphere and altitude differentiation. The results showed that the concentrations of available P were markedly higher in rhizosphere soils compared to bulk soils, and the concentrations did not present a clear altitudinal trend. The increase in the concentrations of available P in rhizosphere soils was significantly related to the LMWOAs that dominated by citric acid, likely through the desorption or ligand exchange rather than acidification effect because of limited range of soil pH. Climate did not alter the distribution of soil available P along the altitude; however, citric acid and soil variables including soil moisture, ammonium nitrogen and microbial biomass P significantly contributed to soil available P. The results of this study indicate that LMWOAs can significantly promote P availability in rhizosphere soils of subalpine forests, and the compensation effect of soil moisture on soil available P for cold stress may induce the higher P availability at higher altitudes.