Non-structural carbohydrates dynamics of Pinus yunnanensis seedlings under three levels of continuous drought stress

There is limited understanding of how drought stress intensity and duration affect the dynamic changes of Non-structural carbohydrates (NSC) in various organs of seedlings, and there is a lack of consistent research results among different species. We performed experiments on the dynamics of NSC in different organs of Pinus yunnanensis seedlings under three continuous drought stresses from March 14 to May 12, 2021, respectively, with four levels of water gradients of suitable moisture (CK), light drought (LD), moderate drought (MD), and severe drought (SD). The results showed that the distribution of NSC in P. yunnanensis seedlings varied with drought stress intensity and duration. The NSC content of each organ (needles, stems, coarse roots and fine roots) showed different trends with the increase of drought stress intensity in different time periods, respectively. After 15d of drought stress, the intensity of drought stress had no effect on needle, stem and coarse root NSC contents, while the fine root NSC contents decreased significantly. At 30d and 45d, drought stress intensity had no significant effect on the NSC content of each organ. However, at 60d, the stem NSC content increased significantly under MD and SD conditions, while the fine root NSC content decreased significantly under SD conditions. With the extension of the drought duration, the coarse root NSC increased while the fine root NSC content decreased under SD conditions. The results showed that the drought duration played an important role in the dynamic change pattern of NSC, only a decrease in fine root was observed at the initial drought phase, and 60d was a turning point when significant changes in NSC occurred at the organ level. This is of great significance to better understand the dynamic changes of NSC in the organ level under drought stress.