Long-term effects of thinning on non-structural carbohydrate and stoichiometric characteristics of Pinus yunnanensis

Abstract The effects of long-term thinning on the nonstructural carbohydrates (NSC) and stoichiometry of trees are poorly understood. Here, root, stem, and leaf samples were collected from a middle-aged Pinus yunnanensis forest thinned in 2012 to determine the content of carbon (C), nitrogen (N), phosphorus (P), sugar, and starch. Our findings revealed that (1) the NSC of the roots and needles increased by 18.94% and 46.95% after thinning, respectively. (2) The P content increased by 36.30%, 63.50%, and 52.16% in the roots, stems, and needles after thinning, respectively. (3) Thinning had no significant effect on the N content in any organ. (4) Long-term thinning affected the distribution of soluble sugars and starches, as well as the content of C and P in different organs. (5) The N:P ratio was 17.96 in the control group and 12.32 in the thinned group, which indicates that P and N were limited in the former and latter, respectively. (6) The phenotypic plasticity index of the stoichiometric characteristics of P. yunnanensis after thinning was lower than that of NSC, and the coefficients of variation of these characteristics in the stems were larger than the coefficients of variation of these characteristics in the organs. Thinning altered the distribution of C and P among the organs, and the stand changed from P-limited to N-limited after thinning. Our findings suggest that appropriate applications of N fertilizer after thinning would improve the quality of the stand.