N–P stoichiometry in soil and leaves of Pinus massoniana forest at different stand ages in the subtropical soil erosion area of China

Plant nitrogen (N)–phosphorus (P) stoichiometry is associated with important ecological processes. However, N–P stoichiometry in soil and plants and adaptive mechanisms of plants to infertile soils in the soil erosion areas remain unclear. We selected 15 plots with Masson pine forest of varying stand ages in typical subtropical soil erosion areas of Southern China. The total nitrogen (TN) and total phosphorus (TP) concentrations in green leaves of Masson pine forest (9.2 and 0.61 g/kg) were significantly lower than the national averages in China (18.6 and 1.21 g/kg). The N:P ratio (TN:TP) of green leaves (15.1:1) was higher than the national (14.4:1) and the global levels (11.8:1 or 11.0:1). Forest soil TN, TP concentrations (0.41 and 0.14 g/kg) were lower than the national averages. The high N:P ratio of green leaves and low soil TP, AP concentrations indicated that P was important in limiting Masson pine forest growth, especially for forests with stand age less than 10 years. Leaf TN, TP resorption efficiencies of Masson pine forests were 26.5 and 64.9 %, and TP in senesced leaves of Masson pine with different stand ages was completely resorbed, suggesting that Masson pine was effective at adapting to nutrient-poor soils. Differences in leaf N–P stoichiometry among different stand ages indicated that nutrient demand varied with Masson pine forest growth stages. Changes in forest soil N–P stoichiometry suggested that Masson pine forest afforestation could greatly improve the soil quality in the eroded lands. However, the significant improvement would take at least a 30-year-long period.