Effect of Different Light Intensities on Photosynthetic Characteristics of Sinojackia dolichocarpa

To elucidate of the optical adaptation mechanism of Sinojackia dolichocarpa under different light intensities,and to provide theoretical implications for the reproduction and ex situ conservation of S.dolichocarpa populations,two-year-old seedlings of S.dolichocarpa were used as the research objects and treated with four light intensities of 100% full light(CK),60% light (L₁),40% light (L₂) and 20% light (L₃). The photosynthetic characteristics of S.dolichocarpa seedlings at different light intensities were measured and analyzed. The results were presented below. Under CK and L₁ conditions,the leaves of S.dolichocarpa seedlings showed a "midday rest" phenomenon of photosynthesis in summer. Under L₂ and L₃ conditions,the daily variation of the net photosynthetic rate (P_n) of S.dolichocarpa seedlings showed a single peak curve. The daily means of net photosynthetic rate (P_n),stomatal conductance (G_s) and transpiration rate (T_r) under L₃ condition were significantly higher than those under CK and L₁ conditions(P<0.05). The maximum net photosynthetic rate (P_nmax),light saturation point (LSP),maximum carboxylation rate (V_cmax),maximum electron transfer rate (J_max),and trisaccharide phosphate utilization rate (TPU) of S.dolichocarpa seedlings under L₃ condition were significantly higher than the other three conditions(P<0.05). The light compensation point (LCP) and CO₂ compensation point (CCP) under CK conditions were significantly higher than those under L₃ condition (P<0.05). The initial light energy conversion efficiency of PSII(F_v/F_m),the actual light quantum yield of PSII(F'_v/F'_m),and the electron transfer rate (ETR) of S.dolichocarpa seedlings were all highest under L₃ condition. In a word,under full sunlight in summer,the seedlings of S.dolichocarpa showed a "midday rest" phenomenon in photosynthesis with a decrease in carbon assimilation efficiency,showing significant light inhibition. L₃ condition was suitable for the growth of young seedlings of S.dolichocarpa with high P_n and strong carbon assimilation ability. The young seedlings of S.dolichocarpa exhibit the characteristics of shade plants.