Effects of tending and thinning on non-structural carbon and stoichiometric characteristics of Pinus yunnanensis

  Objective  Our objective was to explore the mechanism of the effects of thinning on non-structural carbon (NSC), carbon (C), nitrogen (N) and phosphorus (P) stoichiometry of Pinus yunnanensis.

  Method  The middle-aged P. yunnanensis forests were chosen in the Baima River forest area of Yongren County, Yunnan Province of southwestern China, and two experimental sample plots of thinning (thinning intensity of 35.4%) and control were set up to analyze the effects of thinning on NSC and CNP stoichiometric characteristics of P. yunnanensis forests.

  Result  (1) Tending thinning significantly affected the NSC content of needles and branches of P. yunnanensis (P < 0.01), whereas no significant difference on roots was observed. In addition, the NSC content of branch increased by 9.30%, while the NSC content in needles decreased by 3.57%. (2) Thinning had a significant effect on C content of P. yunnanensis branch, P content in needles and stems (P < 0.05), and a highly significant effect on N content in needles (P < 0.01), however, no significant effect was observed on C, N and P content in roots. After thinning, the C content of P. yunnanensis branch increased by 12.93%; the N content in needles increased by 18.04%, and the P content in needles and stems decreased by 27.78% and 55.56%, respectively. (3) The NSC, CNP stoichiometric characteristics showed significant differences among P. yunnanensis organs (P < 0.05). Correlation analysis showed that the P content in needles and roots was significantly positively correlated with soluble sugar content (P < 0.05), while C content in needles was significantly negatively correlated with soluble sugar content (P < 0.05).

  Conclusion  Thinning promots the accumulation of NSC content in stem, branch and root and C content in each organ, whereas needle NSC and P content decreased in each organ, furthermore, distribution pattern of C, N and P in each organ was affected; the growth of P. yunnanensis plantation in this area was limited by N to some extent, and appropriate application of N fertilizer will promote the improvement of stand quality.