| Increases by 1.8-4.0? for global average air temperature are expected in the coming decades.High temperature is often accompanied by waterlogging events in the Yangtze River valley in China,which usually occurres during the cotton anthesis and boll-forming stages.While this period is the most critical for cotton production.Therefore,the experiments about co-effects of elevated temperature and waterlogging on cotton yield and leaf physiological metabolism were established at the Pailou Experimental Station(118°50'E,32°02' N)from 2013 to 2015.The current study mainly focused on the co-effects of waterlogging and elevated temperature on cotton plant growth and yield formation,and discussed the physiological and molecular mechanisms of that the combined two environmental factors affected carbohydrate metabolism,nitrogen metabolism,and antioxidant metabolism in the subtending leaf in the aspects of related substances,related enzyme activities,and key gene expression.1.Co-effects of elevated temperature and soil waterlogging on cotton yieldThe seedcotton weight was significantly decreased under elevated temperature treatment,however,there were inter-annual differences in the boll number and seedcotton yield.The boll number and seedcotton yield in 2013 were significantly lower for EC relative to AC,while boll number was higher than that for AC in 2014 and 2015,which led to higher seedcotton yield compared with AC.Waterlogging significantly descreased chlorophyll content and Pn in cotton functional leaf,suggesting lower source ability,so that lower boll number,seedcotton weight,and seedcotton yield were observed in waterlogged cotton plants in the three experimental years.Among the three production factors,boll number is most sensitive to elevated temperature and waterlogging combined,which is the predominant factor causing the differences on seedcotton yield between treatments.Significant interaction effects on boll number,seedcotton weight,and seedcotton yield were observed.In 2013(higher temperature year),elevated temperature regime exacerbated the negative impact of waterlogging on boll number,which led to lower seedcotton yield under the two aforementioned stresses combined than either single stress.On the contrary,in 2014 and 2015(lower temperature years),elevated temperature treatment increased boll number,and alleviated the reduction in seedcotton yield caused by 3 days of soil waterlogging.2.Co-effects of elevated temperature and soil waterlogging on carbohydrate metabolism in the subtending leaf.Both waterlogging and high temperature limited boll biomass(reduced by 1.19%-32.14%),but effects of different durations of waterlogging coupled with elevated temperature on carbohydrate metabolism in the subtending leaf were quite different.The 6 d waterlogging combined with elevated temperature had the most negative impact on net photosynthetic rate(Pn)and carbohydrate metabolism of any treatment,leading to up-regulated GhSusA and GhSusC expression and enhanced sucrose synthase(SuSy,EC 2.4.1.13)activity for sucrose degradation.A prior exposure to waterlogging for 3 days improved subtending leaf performance under elevated temperature.Pn,sucrose concentrations,Rubisco(EC 4.1.1.39)activity,and cytosolic fructose-1,6-bisphosphatase(cy-FBPase,EC 3.1.3.11)activity in the subtending leaf significantly increased,while SuSy activity decreased under 3 d waterlogging and elevated temperature combined relative to elevated temperature alone.Thus,we concluded that previous exposure to a brief(3 d)waterlogging stress improved sucrose composition and accumulation cross-acclimation to high temperature later in development not only by promoting leaf photosynthesis but also inhibiting sucrose degradation.3.Co-effects of elevated temperature and soil waterlogging on nitrogen metabolism in the subtending leaf.Waterlogging stress not only limited NR(EC 1.6.6.1)and GS(EC 6.3.1.2)activities through the down-regulation of GhNR and GhGS expression for amino acid synthesis,but also promoted protein degradation by enhanced protease activity and peptidase activity,leading to lower organ and total biomass(reduced by 12.01%-27.63%),whereas elevated temperature inhibited protein degradation by limited protease activity and peptidase activity,promoting plant biomass accumulation.Furthermore,2-3? chronic elevated temperature alleviated the negative impacts of a brief(3 d)waterlogging stress on cotton leaves,with the expression of GhNiR up-regulated,the activities of NR,GS and GOGAT(EC 1.4.7.1)increased and the activities of protease and peptidase decreased,leading to higher protein concentration and enhanced leaf biomass for EW3 relative to AW3.The results of the study suggested that exposure to slightly elevated air temperature improves the cotton plants'ability to recover from short-term(3 d)waterlogging stress by sustaining processes associated with nitrogen assimilation.4.Co-effects of elevated temperature and soil waterlogging on antioxidant metabolism in the subtending leaf.Chronic elevated temperature and short-term soil waterlogging in isolation negatively affected leaf performance indicated by lower total chlorophyll content,enhanced OA and ROS,so that ROS-scavenging mechanism in the subtending leaf(included antioxidant enzymatic system and ASA-GSH cycle)were induced.However,acclimation to a brief waterlogging stress(3 d)during the early anthesis stage improves tolerance to continuous elevated temperature at later stages for cotton plant.Since a prior exposure to 3 d waterlogging stress induced higher GR activity and increased ASA concentration,leading to lesser H2O2 and O2-accumulation and preventing membrane lipid peroxidation in the subtending leaf when cotton was subsequently exposed to 2-3? elevated temperature later in development.Our results suggested that higher GR activity and increased ASA concentration caused by a brief(3 d)waterlogging stress played a predominant role in developing a tolerance in cotton against elevated temperature stress by scavenging exceeded ROS in the subtending leaf. |
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