Effect Of Water Stress And Re-Watering On Physiological Characteristics Of Soybean During Its Pod Filling Stage

In order to provided a theoretical basis of water-saving cultivation and water use efficiency of soybean, the impacts of water stress and re-watering of soybean (Qin Dou No.8) during the seedling, blooming and pod filling stage on photosynthetic characteristic, fluorescent characteristic, protective enzyme system and biomass under different soil water treatments was studied. The main results were listed as follows:1. The highest value of Pn, Ci, Tr and Gs of soybean leaves was found when water supply keeping normal during the seedling and podding stage, while the value of Ls and T1were lower. However, Pn, Ci. Tr and Gs have a falling trend with the decrease of soil relative water content, on the contrary, Ls and T1was increased with the decrease of soil relative water content. It can be seen that the rangeability of these indexes under middle-grade water stress was significantly higher comparing that of low-grade, nevertheless, the situation could reverse after re-watering. When soil water was remained65～75%from seedling to blooming stage, low-grade and middle-grade water stress was controlled respectively in pod filling stage after water supply resumed normal, Pn, Tr, Ci and Gs declined extremely with stress increasing, decreased by13.16%,28.60%,7.64%and49.51respectively compared with CK, while Ls and T1improved by48.07%and0.36%separately. The results showed the indexes of leaves performed well after re-watering compared the stress of drought. Moreover, water stress handling in podding period had great influence on Pn. Tr, Ci, Gs, Ls and T1, with large variation m scope.2. While water supply remained normal, with soil relative water content under65-75%from seedling to blooming stage, chla, chlb, car, Fv/Fm. Fv/Fo and ΦPS Ⅱ decreased by24.5%.25.97%.10.71%.38.01%.62.04%and11.11%respectively under middle-grade stress during pod filling period. Consequently, the chlorophyll content during podding period reduced with the soil water stress increasing, which also obviously affected the fluorescence parameters of soybean. Meanwhile, the value of Fv/Fm. Fv/Fo and OPS Ⅱ gradually decreased until re-watering, but the restoration degree ofΦPS Ⅱ was not significant.3. After drought stress, the content of MDA and activity of SOD, POD and CAT all had an increasing tendency with soluble protein decreased due to the cell membrane injury of soybean. It revealed that SOD activity increased significantly under low-grade stress while the activity of POD and CAT changed obviously under middle-grade stress. When soil relative water content under45-55%from seedling to blooming stage with normal water supply or low-grade stress, the POD and CAT activity and the content of MDA sharply dropped by15.58%,38.76%and10.91%respectively with the increase of re-watering degree compared with CK. By contrast, the SOD activity and soluble protein increased by8.91%and2.95%separately.4. As stress level intensified, WUE of simple leaf rose up with the decrease of biomass in podding period, while the situation became converse after water recovery. With water supply keeping normal during the seedling and blooming period, the biomass under middle-stress reduced by19.24%and21.29%in seedling and podding period respectively, while WUE increased by19.87%and9.07%separately, comparing with CK. Then, with low-grade stress from seedling to blooming period, same treatment, comparing with CK, the biomass of plant was reduced by6.16%and6.90%while water utilization efficiency improved by5.41%and8.49%. However, the biomass increased by16.67%while WUE decreased by17.08%with normal watersupplying during the podding period. Besides, with middle-grade stress from seedling to blooming period, biomass of each treatment all increased but WUE was decreased when re-watering in blooming and podding period, which indicated that drought in podding period had a greatly influence on biomass.