| Drought stress has been the one of the key environmental factors that negatively impacts wheat yield in China,and has great effect on crop growth development.As a over winter crop,excess irrigation during the vegetative period of winter wheat results in wastage of water resources since the water need during the vegetative period of wheat is limited.It is,therefore,important to explore the effect of water deficits during different growth stages in winter wheat on grain yield,which can guide towards water-saving cultivation.Pot experiment was conducted using winter wheat cultivar(Yangmai13 and Yangmai 16),which are widely cultivated in the middle and lower Yangtze River Basin,to investigate the effects of water deficit during vegetative period on growth development and grain yield formation and its physiological mechanisms,then the effects of pre-anthesis water deficit adaptation on grain yield under post-anthesis drought stress through leaf photosynthetic capacity and senescence were analyzed.The main results are as follows:1 Moderate water deficit during tillering and jointing stage maintained high grain yield in winter wheat.TM increased grain yield with higher 1000-kernal weight and spike yield,JM had no effect on grain yield while TS and JS decreased grain yield due to the limitation of spikes and grain number,implying that the reduction of spikes and grain number was the main factor that limiting grain yield in severe water deficit during both stages.TS and JS decreased grain number due to the limitation of spikelets and increasing aborted floret number.TM treatment improved leaf area at jointing and anthesis stage,which was beneficial for the biomass accumulation after stress relief.JM treatment decreased biomass accumulation from tillering to jointing and from jointing to anthesis,but increased post-anthesis dry matter accumulation due to high leaf area per plant.TS and JS decreased both leaf area and dry mass.Water deficit during tillering had no effect on CPA,while increased in plants subjected to JM and JS.PTA and CPT decreased slightly in TM and TS,while reduced significantly in JM and JS.The results showed that TM and JM coordinated the contribution of pre-and post-anthesis accumulation to grain yield by improving post-anthesis biomass accumulation.There was a significant positive correlation between grain yield and the accumulation from jointing to anthesis and from anthesis to maturity.In conclusion,enhancing spikes,spike yield and post-anthesis dry matter accumulation were beneficial to achieve high yield in moderate water deficit conditions.2 The enhanced leaf photosynthetic capacity and delayed leaf senescence in moderate water deficit plants are the physiological basis of high yield.Water deficit during both stages decreased net photosynthetic rare(Pn),which in accordance with higher H2O2 and MDA contents.After stress relief,water deficit increased Pn with higher?PS?which was beneficial for compensating the growth limitation.Water deficit treatments during jointing and tillering increased specific leaf weight of flag leaves,and the treatment during jointing being the most stimulatory.Water deficit treatments during vegetative stage increased Pn of flag leaves,the treatment during jointing being the most stimulatory.The maximum photochemical efficiency of Photosystem?,actual photochemical efficiency,the maximum carboxylation rate and photosynthetic electron transport rate and Rubisco content increased in ways similar to Pn in response to water deficit but non-photochemical quenching decreased.Water deficit during vegetative stages enhanced the activities of SOD and CAT,decreased H2O2 content and reduced the content of PLD,PA,LOX and FAA,and also reduced the ABA content,but increased IPA and IAA contents,implying that pre-anthesis water deficit alleviated the membrane lipid and leaf senescence which contributed to higher leaf photosynthetic capacity,biomass accumulation and grain yield.3 The enhanced sugar and nitrogen metabolism in moderate water deficit plants after stress relief is an important feature of improving biomass and nitrogen accumulation.Water deficits decreased SPS,NR and GS activity,and reduced the nitrogen content,but increased the contents of soluble sugars,sucrose and soluble protein.After stress relief,SPS,NR and GS activity were enhanced,while the content of soluble sugars,sucrose and soluble protein decreased fast but still higher than that of control,which lead to fast recovery of Pn and enhance the biomass and N accumulation.Water deficit during vegetative period enhanced the SPS activity and sugar contents of flag leaf,and the treatment during jointing being the most stimulatory.Water deficit during tillering stage had no effect on the activity of NR and GS and the content of nitrogen and soluble protein,while enhanced in plants subjected to water deficit during jointing stage,which implying that moderate water deficit could enhanced the sugar and nitrogen metabolism which is an important feature to improve post-anthesis biomass and N accumulation.Nitrogen accumulation at maturity showed a significant and positive correlation with grain yield which implied that the enhanced nitrogen accumulation capability of moderate water deficit is an important feature for high yield.4 Moderate water deficit adaptation during vegetative period could alleviate the yield loss caused by post-anthesis drought stress in wheat.Compared with FM,TMM and JMM alleviated the yield loss caused by post-anthesis drought with higher grain weight and spike yield which was in accordance with high leaf area,however TSM and JSM significantly decreased yield due to the reduction of spikes.TMM and JMM increased post-anthesis biomass accumulation and its contribution to grain which implied that the higher post-anthesis accumulation was an effective way to alleviate the yield loss.Pre-anthesis water deficit adaptation treatments enhanced photosynthetic capacity due to higher Pn,J and Vcmax with alleviating the reduction of Rubisco and nitrogen content,which was benefical for post-anthesis accumulation.Pre-anthesis adaptation also enhanced SOD and CAT activities and decreased H2O2 and O2-contents and decreased the content of PLD,PA,LOX,FAA and MDA.As compared to non-adaptation treatment,pre-anthesis drought adaption increased ABA content first and then decreased,while increased the content of IPA and IAA.Pre-anthsis adaptation also enhanced the sugar and N metabolisim with higher SPS,SS activities and the content of solulbe sugars,sucrose and nitrogen.In conclusion,pre-anthesis water deficit adaptation treatment enhanced the ability of antioxidant capacity to alleviate membrane lipid oxidation and delay leaf senescence,which can lead to higher photosynthetic capacity and alleviate the yield loss caused by post-anthesis drought.In conclusion,moderate water deficit during vegetative period enchanced antioxidant system,eased membrane lipid oxidation,ameliorated hormone'content,enchanced sugar and nitrogen metabolism which were beneficial for the improvement of photosynthetic capacity contributed to increase the post-anthesis biomass accumulation and high grain yield.Pre-anthesis water deficit adaptation could alleviate the yield loss caused by post-anthesis drought with higher leaf area,photosynthetic capacity and the delaying leaf senescence. |
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