Ecological stoichiometric characteristics and element reserves of three stands in a closed forest on the Chinese loess plateau.

Populus davidiana, Leuchtenbergia principis, and Pinus tabulaeformis are important greening tree species with a cosmopolitan distribution. However, the stoichiometric characteristics and element reserves of stands of these three species are not particularly clear. In this study, we conducted a plot-level investigation of forest stands of these species in the loess area; these have been closed forest stands more than 28 years. Trees were sampled from an area of 50 m × 20 m (in 6, 8, and 9 plots, respectively), which was sufficient for shrub (2 m × 2 m), herbal species, and litter (1 m × 1 m) investigations. The C, N, and P concentrations and the C:N:P stoichiometry in five different soil layers (0-10 cm, 10-20 cm, 20-30 cm, 30-50 cm, and 50-100 cm) and in the leaves, stems, branches, and roots of the plants were examined. The soil element concentrations and density were affected by soil depth. The element content had a significantly negative correlation with soil depth, and element density differed significantly among the soil layers. A particular element in a particular organ differed significantly between the forest stands, and the same element in different organs of the same stand was also significantly different. The C, N, and P element reserves in the soil were considerably higher than in the plants. Our results indicate that there are different stoichiometric characteristics and element reserves of the three stands in a closed forest on the Chinese loess plateau, which may provide a reference when we develop and optimize the structure of forest stands.