Pinus yunnanensis is an endemic tree species in southwest China that has high ecological and economic benefits. Nowadays, global climate change is remarkable, the frequency of drought is increasing day by day, the distribution of rainfall is unbalanced, and even the phenomenon of alternating drought and flood has appeared, which is unfavorable to the growth of P. yunnanensis. We set up four treatments, namely normal water (CK), light drought (LD), moderate drought (MD), and severe drought (SD), and water content was controlled by the weighing method. After continuous drought for 30 days, re-watering was performed for 7 days. The stoichiometric characteristics of non-structural carbohydrates (NSC), soluble sugars (SS), and starch (ST), as well as carbon (C), nitrogen (N), and phosphorus (P), in various organs of P. yunnanensis seedlings were measured. The results revealed significant effects of re-watering on NSC and its components in P. yunnanensis seedlings. The SS and NSC contents in the leaves of P. yunnanensis seedlings treated with SD were significantly higher than those of the control. The C content in the leaves and stems of P. yunnanensis seedlings recovered to the CK level after re-watering under different drought degrees. The contents of N in different organs and P in the fine roots of P. yunnanensis seedlings increased after re-watering with the LD, MD, and SD treatments, while the C/N ratio decreased. In summary, the recovery mechanism of P. yunnanensis seedlings to re-watering varied with the drought degree. The contents and ratios of NSC, C, N, and P in different organs of P. yunnanensis seedlings were significantly affected by re-watering. Combining the phenotypic plasticity index and PCA results, seedlings of P. yunnanensis adapted to drought re-watering by adjusting leaf NSC, leaf P, stem SS/ST, fine root ST, and fine root NSC.

Pinus yunnanensis has high economic and ecological value. The survival of P. yunnanensis has been greatly affected by global warming. This study examines the response of P. yunnanensis seedlings to drought stress and their recovery following rewatering, focusing on growth metrics and C:N:P stoichiometry. This experiment included the four following treatments: CK (water content was 90% ± 5%); LS (water content was 75% ± 5%); MS (water content was 60% ± 5%); and SS (water content was 45% ± 5%). This experiment also included a continuous drought period of 30 days followed by 7 days of rewatering. This study found that drought limited the growth of seedlings, and seedlings could recover rapidly from the damage caused by LS and MS treatments after rewatering, and the recovery of seedlings was greater following LS and MS treatments than following SS. After the drought, the C content in the leaves and stems of P. yunnanensis seedlings could recover to CK levels after rewatering. The N content of each organ and the P content of fine roots of P. yunnanensis seedlings showed an upward trend after rewatering. In summary, the growth of P. yunnanensis seedlings was significantly affected by drought stress, and the recovery mechanism of rewatering varied depending on the degree of drought. Combining the phenotypic plasticity index and principal component analysis, the stem biomass, thin root biomass, root/shoot ratio, leaf C:P, leaf N:P, leaf P, stem C:P, thin root N, thin root P, coarse root N, coarse root P, and coarse root C were the most important indexes for adaptation to drought and rewatering.