C:N:P stoichiometry and homeostasis in leaf, fine root, and soil of Schima superba under different stand ages

To understand nutrient characteristics and stabilization mechanisms of Schima superba plantations with different stand ages, we took stands with five age classes (8, 13, 27, 36, and 54 a) in Youxi County, Fujian Province as the research objects, to explore the variations of carbon (C), nitrogen (N), and phosphorus (P) and their stoichiometric relationships in leaf, fine root, and soil. We further ananlyzed the coupling and homeostasis characteristics between the two components of leaf and fine root of S. superba and soil. The results showed that the C, N, and P contents in leaf and fine root showed a general trend of decreasing and then increasing with the increases of stand age. The minimum values of N (10.38 and 3.45 g·kg^-1) and P contents (0.44 and 0.21 g·kg^-1) of leaf and fine root appeared at the stand with age of 13 a. The C:N and C:P of those two components increased and then decreased with increasing stand age, and both of them reached their maximum values at 13 a. With the increase of stand age, soil C, N, and P contents of woodland showed a pattern of decreasing-increasing-decreasing. All of them were the lowest at 13 a, with 34.27, 1.82, and 0.11 g·kg^-1, respectively; while the maximum values of soil C:N, C:P, and N:P appeared at 13 a, with 19.2, 315.8, and 17.0, respectively. The N and P contents and their stoichiometric ratios of leaf and fine root had significant correlations with soil P content and but not with soil C and N contents. Steady-state model regressions of leaf and fine root C, N, and N:P were all non-significant with absolute stability; and N, P and their stoichiometric ratio of leaf were smaller than those of fine root, but P and C:P of leaf and fine root were more sensitive to change in soil P content. In summary, 13-a was the fast-growing period of S. superba. Soil P content significantly affected leaf and fine root N and P content of S. superba, with the leaf being more sensitive to the variations of soil P content. It was recommended that P fertilizer should be added at the appropriate time to improve soil fertility and focus on the changing of foliar N and P contents.