Effects Of Chilly Temperatures And Drought Stress On Photosynthesis In Mango (Mangifera Indica L.) Trees

This study was carried out in the Xishuangbanna Tropical Botanical Garden, which is situated in southern Yunnan, China. The aims of this study were: (i) to clarify the effect of the normal seasonal chilly temperatures in the winter on the photosynthesis of five mango cultivars (ii) to characterize the effects of simulated extreme chilly night temperature and (iii) drought stress on the photosynthetic physiology of the seedlings of two mango cultivars grown under full light and 50% daylight. The results can be summarized as follow:1- Maximum CO2 assimilation (A_max) of the five cultivars was reduced by 39-54% in the chilly season, with a carry-over effect into the hot and dry season. The maximum quantum yield (F_v / F_m) and actual quantum yield of photosystem II increased from the chilly to the hot and dry and further to the hot and rainy seasons. In the chilly season, Amax, F_v /F_m, non-photochemical quenching (NPQ), and carotenoids:chlorophyll ratio were higher, while the content of malondialdehyde (MDA) and membrane leakage were significantly lower in the cultivars'Guire7','Hong-Xiangya', and'Choke Anand'compared to the cultivars'Zill'and'Tainong'. These results clearly show that the photosynthesis of mango in this region can be strongly suppressed during the chilly season, and the cultivars'Guire7','Hong?Xiangya'and'Choke Anand'are more chilly tolerant than'Zill'and'Tainong'cultivars.2- Night-chilling treatment resulted in strong suppression in net photosynthesis (An), stomatal conductance (g_s), F_v / F_m, and NPQ for both cultivars. Overall, decreases in these parameters were stronger in the seedlings grown in full-daylight than in 50% daylight. The decrease in F_v / F_m was stronger in'Khieo Sawoei'cultivar than in'Choke Anand'cultivar, and the increase of NPQ was relatively higher in'Choke Anand'cultivar compared to'Khieo Sawoei'cultivar. Night chilling resulted in decrease in the chlorophyll content and increase in carotenoid:chlorophyll ratio, content of MDA, membrane leakage, as well as compatible solutes (total soluble sugar and proline) under both irradiances. The recovery of F_v / F_m was relatively quicker in'Choke Anand'than in'Khieo Sawoei'cultivar. The results reveal that cultivar'Khieo Sawoei'is more sensitive to chilling temperature than cultivar'Choke Anand'and shading significantly reduced the harmful effect of chilling night.3- Drought resulted in lower relative water content, An, gs, maximum F_v / F_m, and NPQ in both cultivars under both light levels, moreover, water stress increased the conversion of xanthophyll cycle pigments estimated by leaf reflectance at midday, carotenoid to chlorophyll ratio, as well as the content of MDA, and compatible solutes. The effect of drought was more pronounced in full sunlight than 50% sunlight. After re-hydration, the recovery was relatively quicker in'Choke Anand'cultivar than in'Khieo Sawoei'cultivar. After the treatment of withholding water for 15 days both cultivars in both 50% and full sunlight showed complete recovery in F_v / F_m after five days re-watering. The'Choke Anand'cultivar showed higher resistance to drought than'Khieo Sawoei'cultivar because of the stronger photoprotective and osmotic adjustments of the former cultivar than the later cultivar.