Soil potential labile but not occluded phosphorus forms increase with forest succession.

Quantifying soil P fractions is essential for understanding soil P cycling because these fractions are potential sources of bioavailable P. Here, we investigated whether soil P fractions (i.e., labile inorganic P [P], intermediately available P, organic P, occluded P, and apatite P) differed among three tropical forests at different stages of succession (early, middle, and late) in the Dinghushan Biosphere Reserve (DBR), Southern China. We also determined which soil P fractions was closely related to soil microbial and chemical properties in these forests. Soil microbial biomass and chemical properties (except pH, exchangeable Ca, and Mn) were higher in the late successional forest than those in the other two forests. We found that soil organic and occluded P were the dominant fraction in all three forests and together accounted for 78.9, 84.2, and 78.6 % of total P in the early, middle, and late successional forests, respectively. Soil P fractions and acid phosphomonoesterase activity differed significantly among forest successional stages; intermediately available P and organic P (potential sources of labile P) were highest in the late successional forest, occluded P was highest in the middle successional forest, and acid phosphomonoesterase activity significantly increased in middle and late successional forest. Soil labile P fraction and its potential sources (i.e., intermediately available P and soil organic P) were both positively correlated with soil microbial and chemical properties, suggesting that these properties may play critical roles in maintaining high levels of available or potentially available P fractions during this forest succession. Overall, our study indicates that succession in tropical forest ecosystems may not always lead to lower soil P availability. [ABSTRACT FROM AUTHOR]