[Effects of grafting on photosynthesis of sweet pepper seedlings under low temperature and weak light intensity].

Sweet pepper 'Chifengtexuan' seedlings were grafted onto 'Weishi' and 'Buyeding' rootstocks, treated with low temperature (8 degrees C/ 5 degrees C) and weak light intensity (100 micromol x m(-2) s(-1)) for 7 days, and then recovered under normal conditions (25 degrees C/ 18 degrees C, PFD 550-600 micromol x s(-1)) for 3 days to study the variations of their gas exchange parameters, carboxylation efficiency, and fluorescence parameters, with the own-rooted 'Chifengtexuan' seedlings as the control. The results showed that on the 3rd day of low temperature and weak light intensity stress, the photosynthetic rate (Pn), stomatal conductance (Gs), and carboxylation efficiency (CE) of both own-rooted and grafted seedling leaves decreased more than 50%, and after then, the Pn and Gs tended to stable while CE decreased continually. The intercellular CO2 concentration (Ci) declined first, but enhanced after the 4th day of the stress. Low temperature and weak light intensity decreased the maximal photochemical efficiency of PS II in darkness (Fv/Fm), actual photochemical efficiency of PS II during illumination (phi (PS II)) and electron transport rate (ETR), but increased the initial fluorescence (Fo), which implied that the stress caused definite damage of photosynthetic apparatus. However, the damage diminished after 3 days of recovery. Comparing with those of own-rooted seedlings, the Pn, Gs, CE, phi(PS II), and Fv/Fm of grafted seedlings increased to various degrees, and Fo decreased markedly during the stress. It was concluded that grafting could promote the photosynthetic function, and alleviate the effects of low temperature and weak light intensity on the photosynthesis of sweet pepper seedlings.