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.

As a fast-growing tree species, Ochroma lagopus Swartz has a greater demand for nutrients, and urea and slow-release fertilizer addition can promote the growth and development of O. lagopus. This experiment explored the effects of urea and slow-release fertilizer on the growth and nutrient uptake of O. lagopus plantation forests. The results of the study can provide a theoretical basis for the cultivation and management of O. lagopus plantation forests. At the end of June 2023, a two-year-old O. lagopus was used as the study’s object at Mengwing Farm, Mengla County, Xishuangbanna Dai Autonomous Prefecture, Yunnan Province, China. Fertilizer is applied through root outer ring application. Seven treatments of no N control (CK) and urea and slow-release fertilizers 300 g/plant (N1, H1), 450 g/plant (N2, H2), and 600 g/plant (N3, H3) were set up to determine the breast height, diameter at breast height, as well as the nutrient contents of leaves, branches, roots, and soils of the trees. The DBH and tree height were higher under N addition than in the CK, and both were highest in H3 at 90 d after fertilization, with 16.92% and 14.64% higher than CK, respectively. The overall change in C content of each organ was not obvious, N content increased with the increase in fertilizer application, and the change pattern of P content was not consistent. Soil N content showed a significant increase with the increase in N application, while P and K content showed a trend of increasing and then decreasing, and soil N content of slow-release fertilizer treatments was higher than that of urea treatments under the same amount of N application. The soil N content was higher in the slow-release fertilizer treatment than in the urea treatment regardless of the amount of N applied. The soil N content was highly significantly positively correlated with the N content of leaves, branches, and roots. There was a highly significant allometric growth relationship among the C, N, and P content of each organ. The N addition had a significant effect on the growth and the nutrient content of each organ and soil. O. lagopus mainly adapted to changes in the soil N content by adjusting the N and P content of each organ, and the optimal effect was observed in H3. In the future, an appropriate amount of P fertilizer should be applied to complement N fertilizer, urea and slow-release fertilizer can also be applied.