Effects Of Drought And Rewatering Of Maize And Their Leaf Water Conditions For Critical Photosynthesis

The frequency and intensity of extreme drought events are gradually increasing,under global climate change,which is a serious threat to food security.Maize is one of the most important three staple crops,to date,drought stress is the main factor limiting maize production.Therefore,it is urgent to understand the response process of maize to drought and rewatering,reveal the mechanism of drought disaster,to provide the basis for drought monitoring and early warning and formulate reasonable drought avoidance countermeasures.This study used the field experiment data of continuous drought in different growth stages with different irrigation amount of summer maize from 2013-2015 and continuous drought and rewatering in different growth stages with different irrigation amount of spring maize in 2016.The effect of drought and rewatering in maize different growth stages was analyzed and the leaf water content(LWC)for critical photosynthesis of maize(the point of photosynthetic capacity reached maximum and minimum and photosynthesis changed from being limited by stomatal limitation(SL)to non-stomatal limitation(NSL))was obtained.The main conclusions are as follows:(1)Under the condition of continuous drought in different growth stages with different irrigation amount,the LWC of summer maize at different leaf positions decreased with the decreasing of soil water content,while its decreasing rate for the first fully expanded leaf(Top1)was faster than that for the third leaf(Top3),at the same time,the maximum LWC for Top1(84.9%)was greater than Top3(82.5%).After drought stress in different growth stages with different irrigation amount,the alleviating effect of rewatering on LWC of spring maize was different,the recovery degree of spring maize LWC after rewatering was closely related to the occurrence time of drought stress.(2)Under the condition of continuous drought in different growth stages with different irrigation amount,leaf area,LWC,steam water content,net photosynthetic rate,transportation rate and stomatal conductance of summer maize were sensitive to the change of soil water content,and their responses were different to soil water content.The decrease of soil water content firstly caused the decrease of stem water content,then led to the decrease of LWC,then affected the photosynthesis intensity and leaf area expansion,and finally affected the dry matter accumulation and even caused the reduction of total dry weight.(3)Under the condition of continuous drought in 3^rd,7^th and jointing stages with different irrigation amount,summer maize photosynthesis at different leaf positions changed from being determined by SL to NSL,and its order was from up leaf to down leaf,this phenomenon occurred first at the top leaf.The LWC at which the SL transformation point occurred in Top1(75.5%±1.5%-75.7%±1.3%)was higher than that at which the change occurred in Top3(73.2%±1.1%-73.4%±1.6%).The LWC of Top1 had a good indication of water stress in summer maize and could be taken as the monitoring indicators for maize drought.(4)The relationship between maximum carboxylation rate at the reference temperature of 25?(Vcmax25)and LWC of summer maize at Top1 showed a significant quadratic curve under the condition of continuous drought in different growth stages with different irrigation amount,and the LWC was 82.5%±0.5%when Vcmax25 reached the maximum value(42.6±3.6?mol m^-2 s^-1),while the LWC was67.6%±1.2%when Vcmax25 was zero.(5)The LWC(75.4%±0.38%)of Top1 when spring maize photosynthesis changed from being determined by SL to NSL was the critical leaf water condition to determine the recovery degree of maize Vcmax25.The drought stress had obviously inhibitory effect on Vcmax25,it led to the maximum value of Vcmax25 for drying process was greater than that for rewatering process.The drought stress changed suitable LWC range for Vcmax25,it led to different LWC when Vcmax25 was zero and reached maximum value.The LWC was 70.8%and 69.0%when Vcmax25 was zero,while the LWC was 77.4%and 74.5%when Vcmax25 reached maximum value for drying and rewatering process.