Physiological And Ecological Response Of Soybean Seedlings To Drought And High Temperature Under The Background Of Climate Change

In recent years, with the climate becoming warm,the extreme weather disasters particularly droughts and high temperatures disasters frequently occur,pose a serious threat to the social,economic and environmental sustainability.Drought are one of the most influential natural disasters in the word,which can cause the most serious economic losses in agriculture.Drought is different from floods,due to its own characteristics including the slow occurrence of process,a huge sphere of influence and the difficult to quantify the non-engineering loss,so it is much difficulty to understand and predict it for human beings.Therefore,more attention is focused on how timely and effectively predict the occurrence and development of drought and how to make effective and reasonable assessment on the impact of drought in borne and abroad.On the other hand,high temperatures will increase the evaporation of surface water and reduce the effective soil moisture,thereby further aggravate the exent of droughts,which can lead to more severe water stress on crops and make the agro-ecological environment more fragile,therefore, To study the physiological response of typical crops to drought stress is an important basis for the evaluation of drought risk.This study area is Huang-Huai region,which is the most water-scarce area in china and the most sensitive area to the climate change. Soybean is one of the major crops in this region,which is the most sensitive to water in legume crops.In order to undersand the crops in Huang-Huai area how to resist water and high temperature stress wholly and completely,We selected yudou 19 as our material, material, studied photo synthetic characteristics,antioxidant system and osmotic adjustment as well as the repair ability after different stage re-watering by water controlled experiment and also researched the photosynthetic characteristics under two levels of high temperature stress process which carried on in the artificial climate chamber.The water controlled experiment was set four water levels,that is,CK light water stress,middle water stress and severe water stress.The main results are as following:1.With the strengthening of drought stress,the contents of free proline and soluble sugar significantly increased.But along with the period of drought stress continued,the contents of soluble sugar was tend to decrease.After re-water the contents of soluble sugar could decreased to that of CK.However,the contents of free proline could not recovery to that of CK under NS at end stage.It showed that after re-water soybean had a certain compensatory growth effect which was closely related with the stress time and stress intensity.Under high temperature stress,the contents of free proline and soluble sugar increased consistently with the treatment prolonged and the stress aggravated.They could increased to that of CK.2. Along with the period of drought stress continued, the MAD content showed a trend of up-down-up. SOD activity was tended to increase and then decreased.SOD and MDA of NS at any stage could not recovery to that of CK when re-watering.Under high temperature stress, SOD and POD activity was tended to increase and then decreased. contents of malondialdehyde (MDA) were gradually increased with the time of high temperature continuing.3.With the prolonged of drought stress,the content of chlorophyll under mild stress firstly increased then decreased.The content of chlorophyll under moderate stress and severe stress had a substantial decline.After re-water the content of chlorophyll went up and reached to the level of control. Under high temperature stress,the content of chlorophyll a,b and Chl.a/Chl.b were both showed increase and then decreased.4. The water stress resulted in progressively decreases in net photosynthesis rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr), respectively, WUE increased a little under L S and decreased to some extent under MS, but obviously decreased under NS. The intercellular CO2 concentration (Ci) decreased at light stress and moderate stress, but increased at high stress, which indicated that the decline of Pn was caused by stomatal restriction under light stress and moderate stress, but non-stomatal restriction under high stress.After re-watering,Pn,Tr,Gs and WUE recovered with different degrees.Compensation effect was visible before serious stress when the photosynthesis indexes recovered greatly,while they recovered little under serious stress due to the hurt of physiological function of soybean.The net photosynthetic rate decreased under high temperature. The longer the stress is, the more significant the amplitude of Pn descended. The Gs also decreased as the stress degree increased or the time prolonged. The Tr showed a trend of down-up-down.WUE decreased at first and then increased to some extent. The decline of Pn was caused by stomatal restriction at the initial phase of high temperature stress,but non-stomatal restriction at the latter phase of high temperature stress.