Abstract: Forest growth is commonly limited by soil phosphorus (P) availability. Understanding the relationships between soil P availability and the community structure of soil phoD harboring microorganisms and bacteria in different stand densities of Pinus massoniana plantations would provide a theoretical basis for selecting an appropriate management strategy. We analyzed the community structures of soil phoDharboring microorganisms and bacteria under four density stands of Pinus massoniana: low density (2500 trees·hm^-2), medium density (3300 trees·hm^-2), mediumhigh density (4500 trees·hm^-2), and high density (6000 trees·hm^-2) stands. We used the HiSeq 2500 high-throughput sequencing method to analyze soil microbial community. In addition, the effects of stand density on the community structures of microorganisms were analyzed from an ecological stoichiometry perspective. The results showed that the concentrations of soil organic C and needle leaf P were the highest in the medium-density stands. Soil C∶N ratios, nitrate concentration, exchangeable calcium concentration, six P fractions (CaCl-P, citrate-P, HCl-P, total available P, enzyme-P, and microbial biomass P), acid and alkaline phosphomonoesterase activity, and needle leaf C∶P and N∶P ratios were the lowest in the medium-density stands. The community structure of soil phoDharboring microorganisms and bacteria were significantly different among the four density stands. The Shannon diversity of the microbes was not significantly different among the stands. The relative abundance of the dominant genus Bradyrhizobium was the lowest in the mediumdensity stand. Results of redundancy analysis highlighted the role of soil pH and nutrients in driving variations in the community structures of soil phoDharboring microorganisms and bacteria among different density stands, indicating that the differences in community structures of soil phoDharboring microorganisms and bacteria were driven by stand density and soil factors, with greater contribution from stand density. These results suggest that medium-density Pinus massoniana plantation is least limited by P availability, and thus is a suitable plantation density.

Key words: Pinus massoniana, density, needle leaf, soil P fraction, phoDharboring microorganisms.