Study On Effects Of CO₂ Enrichment And High Temperature On Photosynthesis And Water Use In Diospyros Kaki

The research was carried out at horticultural experiment station and lab of protected fruit trees, Shandong Agricultural University in 2007 and 2008. Two-year-old Diospyros Kaki (Diospyros Kaki Huayusuo, Haikuman, Yidou, Cilang) were used and changes of CO₂ concentration, temperature, soil moisture conditions simulated in the experiment. Effects and mechanisms of elevated atmospheric CO₂ on photosynthesis and water use, and effects of CO₂ concentration and temperature on chloroplast ultrastructure, light and CO₂ response parameters, photosynthesis and relative factor were studied. The changes of photosynthesis, osmotic accumulation, protective enzyme activity under elevated atmospheric CO₂ , temperature and water stress were also investigated. The main results were as follows:1. Photosynthetic rates Huayusuo, Haikuman and Yidou were increased by elevated atmospheric CO₂ while photosynthetic acclimation was observed in Cilang. Different varieties had different optimum temperatures. Optimum temperature of Huayusuo, Haikuman, Cilang was higher than that of Yidou. Elevated atmospheric CO₂ and high temperature manifested as synergistic effect in promoting photosynthetic rates of Diospyros Kaki. But the synergistic effect only behaved in varieties with higher photosynthesis optimum temperature or without photosynthetic acclimation.2. The results of chamber experiment showed that the light compensation point (LCP), CO₂ compensation point (CCP) declined while the carboxylation efficiency (CE), apparent quantum yield of carbon assimilation (AQY), Fv/Fm,ΦPSII and ETR increased along with the rise of CO₂ concentration for the Diospyros Kaki varieties except Cilang, which could alter the ability of utilizing low light and CO₂ of Diospyros Kaki. Moreover, respiration rate of most varieties of Diospyros Kaki was promoted by elevated CO₂ concentration.3. The results of chamber experiment showed that: in Huayusuo, Haikuman, and Yidou, elevated CO₂ concentration increased the contents of Chla, Chlb, Car, and Chl(a+b), especially the contents of Chlb and Car. 4. The results of chamber experiment showed that: width of upper and lower epidermal cells, number of chloroplast, grana and amella could be increased by elevated CO₂ concentration, as proved in Huayusuo. In suitable growth temperature range, high temperature was conductive for the morphogenesis of leaves, including the quantity and length increase of chloroplast and width increase of lower epidermal cells.5. The results of open top greenhouse experiment showed that photosynthesis and water use efficiency were promoted by elevated CO₂ concentration under water stress. High temperature promoted the activity of optical synthase, and gave plants in optical water conditions strong photosynthetic capacity. However, high temperature reduced the photosynthetic promoting effect of elevated CO₂ concentration on photosynthesis and reduced Pn.6. In the open top greenhouse experiment, elevated CO₂ concentration enhanced activity protective enzymes via changing the osmotic adjustment ability, so as to reduce the damage of water stress and increase the stress resistance ability. The osmotic adjustment ability and protective enzyme activity under stresses of elevated CO₂ concentration, temperature and water differed in different Diospyros Kaki varieties, showed as: Haikuman>Huayusuo.