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.

Slope aspect and slope position have an important influence on plant growth by changing the microclimate and soil conditions such as light, temperature, moisture, and nutrients. In this study, 15-year-old Sapindus mukorossi forests with different slope aspects and positions were selected and the differences in tree height and diameter at breast height (DBH), leaf non-structural carbohydrate (NSC) characteristics, and leaf–soil nitrogen (N), phosphorus (P), and potassium (K) stoichiometric characteristics between sunny and shady slopes, and upper, middle, and down slope positions were compared and analyzed. The results show that the tree height and DBH of S. mukorossi were better in the same slope aspect and lower slope position, while in the same slope position, the tree height and diameter at DBH were better on the shady slopes. In the upper slope position, the starch content on the shady slope was significantly higher than that on the sunny slope, and the NSC content was significantly higher than that on the sunny slope. On shady and sunny slopes, S. mukorossi is mainly limited by N. The leaf and soil P content of S. mukorossi on the sunny slope was the highest and significantly higher than that on the upper slope. The coefficient of variation of each index of S. mukorossi on the shady slope and the sunny slope was medium and below. Soil N/P, soil N, soil N/K, soluble sugar/starch, leaf P, leaf K, leaf N, and soil K had strong plasticity under different slope aspects. Therefore, it indicated that the shady slope and down slope were more suitable for S. mukorossi.

Phytoliths are widely used in plant taxonomy, paleoecology, soil silicon cycling, and agricultural archaeology. Bamboo has a strong capacity for silicon absorption, and there are some phytoliths in various organs. In this paper, the leaf organs (leaf blade, leaf sheath, culm sheath, and culm blade) of three kinds of bamboos [B. vulgaris (Bambusa vulgaris), B. tulda (Bambusa tulda), and B. dolichoclada (Bambusa dolichoclada)] were studied; the content, concentration, particle size distribution, and morphological characteristics of phytoliths in leaf organs were analyzed to explore the differences of phytoliths in different functional leaf organs of bamboo. The results showed that the content and concentration of phytoliths were the highest in the leaf sheath and the lowest in the culm sheath, and the content and concentration of phytoliths in the leaf blade and culm blade were between them. For different bamboo species, the order of phytolith content was B. dolichoclada > B. tulda > B. vulgaris, while the phytolith concentration was the opposite. The highest values of phytolith particle size peak distribution in the leaf sheaths were the opposite to those in leaf blades, culm sheaths, and culm blades. The particle sizes of phytoliths of the three bamboo species showed a similar trend. Only a few larger phytolith particle sizes were distributed in leaf blades and culm blades when they were larger than 400 μm. A total of 25 types of phytoliths were identified, and the leaf sheaths were mainly elongate and rondel phytoliths. The leaf blades are mainly saddle and rondel phytoliths with a unique phytolith morphology. Culm sheaths are dominated by rondel, scrobiculate, and acute phytoliths. Culm blades are similar to leaf blades but have a characteristic phytolith morphology. In addition, saddle phytoliths were the most abundant in the leaf blade and the least in the culm sheath, while rondel phytoliths were the most abundant in the culm blade and the least in the leaf sheath. The parameters of long-saddle phytoliths are different in different bamboo species and leaf organs. According to the long saddle phytolith parameters of different bamboo species, different bamboo species can be quantitatively distinguished to a certain extent. Therefore, this study not only helps to understand the differences in phytoliths in different bamboo species and leaf organs, but also provides a theoretical basis for bamboo species classification.