Ecological stoichiometry of leaf-litter-fine roots in mixed plantations in mountainous area of Southern Ningxia, China.

The southern mountainous areas in Ningxia are representative regions of the Loess Plateau, with extremely fragile ecological environment. Large area of pure plantations established during the project of Grain for Green has suffered from poor nutrient availability and biodiversity loss, while planting mixed plantations is commonly consi-dered as an effective way to improve the ecological benefits. We selected + mixed plantation, + mixed plantation, pure plantation and pure plantation located ina Ningnan mountainous area as test objects. Based on the theory and method of ecological stoichiometry, we measured the C, N and P contents of leaves, litter and fine roots to understand nutrient cycling characteristics of different plantations. The results showed that there was significant difference in foliar stoichiometry of each tree species within the four plantations. leaves had the highest C content in the + mixed plantation, and leaves had the highest N and P contents in the + mixed plantation. N content of and leaves was significantly higher in mixed plantation compared with that in pure plantation. There was no significant difference in litter biomass, litter C, N, P contents and stoichiometric ratios between the pure and mixed plantations of . Litter biomass in pure plantation was significantly higher than that in + mixed plantation, while litter C content was significantly lower than that in the mixed plantation. Fine root biomass decreased with increasing soil depth in the four plantations, with total fine root biomass being the highest in the + mixed plantation. N content and N:P of fine roots in the + mixed plantation were higher than those in and pure plantations. There was significant negative correlation between N content in leaves and fine roots of + mixed plantation. There were significant negative correlations between the N content of leaves and litter, as well as between the P content of leaves and fine roots in the + mixed plantation. P content between litter and fine roots in pure plantation was significantly negatively correlated. Nutrient status of mixed plantations was better than pure plantations in the Ningnan mountainous area, with the mixed plantation of and being the best. Mixed planting reduced nutrient limitation on plant growth to a certain extent.