Effects of shading and drought on photosynthetic characteristics of Bletilla striata seedlings

This study aimed to elucidate the adaptive mechanisms of photosynthetic physiological characteristics of Bletilla striata seedlings to shading and drought and provide a scientific basis for improving their cultivation efficiency. The experiments were performed using 2-year-old B. striata seedlings. A total of nine interaction treatments, each involving different levels of shade and drought, were set up to study the changes in the photosynthetic characteristics and chlorophyll fluorescence parameters of B. striata seedlings under the dual stress of shade and drought. The results showed that the levels of photosynthetic pigments significantly increased in all shade treatments. The stomatal conductance was significantly reduced under heavy shade conditions; however, changes in chlorophyll fluorescence parameters were not significant under various shade treatments. Under drought stress, the net photosynthetic rate of B. striata was affected by "stomatal limitation", with a significant increase in chlorophyll a and carotenoid contents. Severe drought stress resulted in a significant reduction in the transpiration rate and stomatal conductance, whereas chlorophyll fluorescence parameters did not change significantly. The interaction of shade and drought stress had a greater effect on the photosynthetic characteristics of B. striata. Stomatal conductance, transpiration rate, net photosynthetic rate, maximum quantum yield of Photosystem Ⅱ (PSⅡ) photochemistry (F_v/F_m), and maximum primary yield of PSⅡ (F_v/F_o) were significantly reduced under the combined effect of severe drought and severe shading. The photosynthetic pigments were significantly reduced under moderate drought and severe shading. Although the photosynthesis characteristics and chlorophyll contents of B. striata leaves varied greatly between treatments, chlorophyll fluorescence parameters remained relatively stable, indicating that shade, drought, and shade-drought complex stresses did not cause irreversible damage to the B. striata photosystems.