Effect of combined low temperature, poor light and salt stress on photosynthetic characteristics of pepper seedling leaf

Photosynthetic parameters, and light and CO2 requirement characteristics were analyzed to determine effects of combined low temperature (18 ℃/10 ℃, day/night), poor light (80 mmol·m^-2·s^-1) and salt stress (70 mmol·L^-1 NaCl) on photosynthetic characteristics in pepper leaf. Net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) decrease under single or combined low temperature, poor light and salt stress. Pn under low temperature and salt stress decreases by 71.28% after treatment for 15 days compared with the control. The limiting factor of different stresses regarding decreasing Pn is different for pepper leaves. Except for the increase in apparent quantum yield (AQY) for leaves under poor light, and CO₂ compensation point (CCP) for leaves under low temperature and poor light, all other stresses suppress light compensation point (LCP), light saturation point (LSP), AQY, photosynthetic rate at light saturation point, CCP, CO₂ saturation point (CSP), carboxylation efficiency (CE) and maximum reproductive rate of RuBP. The degree of suppression is higher in leaves under combined low temperature and salt stress, followed by those under combined low temperature, poor light and salt stress. It implies that the response mechanism of photosynthetic characteristics of pepper leaves under combined low temperature, poor light and salt stress is different from that of single or double stress. Poor light could, to some extent, relieve the drop in photosynthetic capacity of pepper leaf under low temperature and salt stress.