Effects Of Soil Water Availability On Leaf Photosynthetic Parameters And Drought-tolerance Of Pear-jujube Tree

Using automatic weighing and irrigation system, called load cell system, pear-jujubetrees were exposed to suitable soil water content, medium and severe water deficit(corresponding to soil water contents between75%±5%,60%±5%,45%±5%of fieldwater capacity, respectively). The diurnal variations of photosynthetic parameters and droughtresistance relating to the physiological and biochemical paremeters under different soil watercontents were investigated, to explore the effective soil water content which to makepear-jujube tree growing and developing better. It can provide scientific theoretical guidanceto jujube cultivation management for arid and semi-arid regions. The results show that:(1) Under decreased soil water contents, daily water consumption per plant reducedgradually, severe water deficit was significantly lower than other treatments, and the totalwater consumption per plant dropped significantly with the increase of stress level. Inaddition, the biomass decreased gradually in the part of root, stem and leaf of pear-jujube tree,the root/shoot ratio increased.(2) Compared to the suitable soil water content, medium water deficit did not havesignificant effect on diurnal variations of leaf photosynthetic parameters, while severe waterdeficit significantly reduced leaf net photosynthetic rate (Pn), transpiration rate (Tr), stomatalconductance (Gs), intercellular CO2concentration (Ci), and light use efficiency (LUE), butincreased the stomatal limitation value (Ls) and the water use efficiency (WUE).(3) Severe water deficit significantly reduced pear-jujube leaves Amax, LSP, but increasedthe LCP, Rd. Therefore, the range of photosynthetic effective radiation reduced. And under themedium water deficit, Amax, LSP were all similar to the suitable soil water content, but thevalues of LCP and Rdwere all minimum, the value of AQY maximum. Therefore, the soilwater content of60%of field water capacity helped to improve photosynthetic activity ofmesophyll cell of pear-jujube tree.(4) Under decreased soil water contents, the contents of osmotic substances (such as thecontents of soluble sugar, starch and proline) were all no significant differences. The studysuggested that the several kinds of chemical compound may not have a major role for osmotic adjustment ability of pear-jujube leaves under the condition of this experiment, it may also berelated to drought resistant mechanism and metabolic characteristics of pear-jujube tree itself,and it remains to be further tests.(5) Medium water deficit did not have significant effect on leaf malondialdehyde (MDA)content, the activity of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT)were significantly increased, suggesting the SOD, POD and CAT of pear-jujube leaves werevery sensitive to water deficit. This is good for removing reactive oxygen species. Howere,the activity of SOD and POD and the contents of ascorbic acid (ASA) and glutathione (GSH)increased significantly, but it still could not eliminate the serious damage of pear-jujubeleaves membrane system caused by severe water deficit. Therefore, significantly increasedMDA content, pear-jujube leaves membrane permeability increased, membrane lipidperoxidation and membrane damage increased.In conclusion, for pear-jujube tree, soil water content of60%±5%of field watercapacity was not a significant effect of the non-biological stress. But the MDA contentincreased significantly under severe water deficit, and it caused serious harm to pear-jujubeleaves membrane system. Therefore, in the production practice, when the soil water contentdown to45%±5%of field water capacity, needing timely irrigation, in order to improve theeffectiveness of the soil water.