Nitrogen and Phosphorus Distribution and Relationship in Soils and Plants under Different Aged Chinese Fir Plantation

As essential nutrients for plant growth and development, the balance of nitrogen (N) and phosphorus (P) between soils and plants is a key component to ecosystem stability. In this study, we examined the distribution of nutrients in the soils and different organs of Chinese fir (Cunninghamia lanceolata) in Hunan Province, southern China. Additionally, we investigated the nutrient concentrations in soil layers (0-80 cm depth) and in plant organs, and the total biomass of 10-, 20-, and 30-year-old plantations. The results suggested that the nutrients in the soil were aggregated in the surface layer. The highest and lowest values of N concentrations in 0-80 cm soil layers and P concentrations in 0-40 cm soil layers were both in 30-year-old plantations and 20-year-old plantations, respectively. Nitrogen in the organs of Chinese fir in all plantations and P concentrations in the organs of 20- and 30-year-old trees decreased in the following order: leaves, fine roots, coarse roots, and stems. Total biomass (N and P pools of four organs) increased consistently with stand age increase, and N and P pools were the highest in leaves and stems, respectively. There were significant, positive correlations between N and P in the soil (0-80 cm), and organs, respectively, and also between N concentrations of fine roots and that of 0-10 and 10-20 cm soil, respectively. In Chinese fir plantations, concentrations of nutrients in specific tree organs and the soil were correlated positively, which can only partially explain the balance of nutrients within the plant-soil ecosystem. This study suggested that incorrect harvesting patterns may effectively deprive the forest ecosystem of valuable nutrients that would ordinarily have been returned to the soil.