Effects of phosphorus resorption on bioactive phosphorus of different-aged Pinus massoniana plantations

Abstract

Phosphorus (P) is an important nutrient element in the photosynthesis process of plants. The effect of stand age on P nutrient dynamics in subtropical plantations is unclear. In this study, the mechanisms of above- and belowground P cycling in subtropical P. massoniana plantations of different stand ages (5, 9, 19, 29 and 35 years) were investigated. The percentage of metabolic P in leaves exhibited an initial rise and subsequent decline with stand age of P. massoniana throughout the growing season, culminating in a metabolic P proportion of 34%–68% in litter. During the non-growing season, the main change in the P components of P. massoniana fine roots was a transition from metabolic P to residual P. Relative to during the growing season, soil ligand P fractions decreased by 7%–22% and exchangeable P fractions increased by 0–16% in the non-growing season. Organ P components tended to decrease with increasing stand age, mainly due to the gradual decrease in soil-bioavailable P, a trend alleviated by litter input. The generation of dissolved P by soil phosphatases would limit the reduction in soil-bioavailable P caused by leaf P resorption to some extent. The differences in leaf organ P components between the growing and non-growing seasons are attributed to the allocation of P by the P. massoniana. Overall, the results of this study provide a basis for exploring the mechanisms of soil bioavailable P and soil P enzyme-mediated organ P component allocation in P. massoniana forests. These findings will help improve the management of P-limited P. massoniana plantations to enhance their productivity.