Soil C, N, P, K and Enzymes Stoichiometry of an Endangered Tree Species, Parashorea chinensis of Different Stand Ages Unveiled Soil Nutrient Limitation Factors

Abstract

Parashorea chinensis is an endemic tree species in China and an endangered species of the Dipterocarpaceae family. This study contributes to the understanding of soil fertility management during the relocation and conservation of P. chinensis and the restoration of its natural communities by doing an ecological chemometric investigation of the factors limiting soil nutrients in P. chinensis plantations. To investigate the variation in rhizosphere and non-rhizosphere soil nutrients, microbial biomass, and extracellular enzyme activities, we chose pure plantation stands of 6 ages in the subtropics and calculated stoichiometric ratios. The results show that (1) soil pH is strongly acidic (pH < 4.6) and is less influenced by the stand age, and the soil carbon (C), nitrogen (N), and phosphorus (P) content limit soil microorganisms at all stand ages; (2) the availability of soil N, P, and K elements is an essential factor driving P limitation in the growth of P. chinensis and its soil microbes; (3) stand age has a significant effect on the soil C/N, C/P, N/P, C/K, N/K, and P/K, the stoichiometry of microbial biomass C, N, and P, and the stoichiometry of C, N, and P acquisition enzyme activity. Soil microbial biomass C, N, and P stoichiometry are more sensitive indicators of nutrient limitations than the stoichiometry of enzyme activity and nutrient content; and (4) there was a significant correlation between microbial biomass C, N, and P stoichiometry and soil C/P and N/P, as well as a highly significant (p < 0.01) correlation between the stoichiometry of the enzyme activity and Vector L and Vector A. In conclusion, the plantations of P. chinensis in this study area were established on acidic phosphorus-poor soil, and the ecological stoichiometry of the soil reveals nutrient limitations and its variation with the stand age. P availability plays a key role in the growth of P. chinensis and in improving the rhizosphere microbial community. Therefore, soil effectiveness should be dynamically assessed during the cultivation and relocation conservation of P. chinensis, and a soluble P fertilizer should be supplemental over time in the trees’ root distribution area.