The Introduction of Broad-Leaved Tree Species Drives The Process of Nutrient Cycling in Forest Soil

Abstract Background Pure cypress forests experience problems such as reductions in biodiversity, lowered capabilities for water and soil conservation, decreased underground productivity and land degradation. To improve the conditions of pure forests, we studied the effects of mixed gaps on the cypress (Cupressus funebris) pure forest, selecting the Chinese toon (Toona sinensis), which is a deciduous broad-leaved tree, as the mixed tree species. We examined the variations in the concentrations of C, N, and P and their ratios in plant tissues, litter and soils in different seasons in pure cypress forests with 4 different sizes of mixed gaps (50, 100, 150, 200 m2). Results The leaf N:P ratios of cypress and Chinese toon were 10.77 and 12.74, respectively, and N was the main limiting factor for tree growth in the study area. The N and P resorption rates of the cypress pure forest were 57.4% and 60.7%, respectively, and mixed gaps with Chinese toon increased the resorption rates. An analysis of correlations among leaf-litter-soil stoichiometry indicated that the correlations between the soil nutrient elements and the corresponding plant leaves and litter increased when the broadleaf tree species was introduced into the cypress pure forest. Conclusions These results indicate that the introduction of broad-leaved species was favorable for triggering the forest soil nutrient recycling process.