| Soybean(Glycine max(L.)Merr.)breeding history in China was only decades,but it has been made a big progress for the yield.During crop breeding,people always selecte the target plant directly by experience.Crop yield performance is connected with their physiological,phenotypic traits,but there was no consensus for breeding the ideal plant.Trait-based comparative approach was widely applied in ecology to seek why and how plants occupy their niches and the components of ecosystem operate differently across environments.Now,this approach was widely applied in agroecosystem,people through this approach to identify the intraspecific variation and how this variation influence the crop yield performance in agroecosystem.For the plants in the wild condition,the drought adaption is the ability of survival,while for the crop plants,the ability to get higher yield,yield stability and water use efficiency under water deficit condition are the references to the drought adaption(Blum,2009).In semiarid area,water shortage is the main limited fact to the yield,how to tradeoff between the water use and plant growth is the key to the soybean yield performance.In this study,we applied the trait-based comparative ecological approach to identify the traits and inter-trait linkage that related to the yield performance in the water limited condition,those traits may be selected by breeders unconsciously.By this way,we could get more information for breeding and agronomic practice in future.In order to get that target,we selected four modern cultivars(ZH,J19,J21 and J12)that released in resent twenty years and four landraces(LX,HD,Y and B)that had different yield.We conducted the pot experiment(experiment 1)in 2015 and two years of field experiments(experiment 2 and 3)with different precipitation in 2016and 2017.In experiment 1,we set two treatments:drought-rehydrate cycles(rehydrate the soil water content(SWC)to 100%pot water capacity(PC)when the SWC drop to20%PC,WS)and well water condition(keep the SWC at 80%-100%PC,WW),to determine the stomatal conductance(gs),photosynthetic rate(Pn),leaf hydraulic conductance(Kleaf)and leaf relative water content(RWC)changing with the treatments,and calculated the water use and yield performance at harvest time,to identify the contribution of physiology response to drought stress and the differences of biomass allocation to the yield.In experiment 2,under different precipitation years,we use same 8 genotypes with randomized design,we sampled at flowering stage,fulling pod stage and maturity stage,to determine the different biomass accumulated during vegetative growth stage and reproductive stage,recording the branch numbers,seed size,harvest index(HI)and yield formation characters.In experiment 3,under the same two years condition,we set three densities(12.5 plants/m2,25 plants/m2(local plant density)and 50 plants/m2)to control the leaf area index,three replications,every plot had 12.8m2,totally had 72 plots,to recorde the leaf mass per area(LMA)and LAI at different genotypes,precipitations,growth stages and plant densities,recording the Pn changed with days,yield,water use efficiency.From those experiments,we found:1.During progressive drought,modern cultivars physiological response was more sensitive to the drought stress:gs(65–67%vs 61–63%),Pn(60–62%vs 52–54%)and Kleaf(50–67%vs 36–48%)were decreased at higher SWC than the landraces,this could help conserve water use and delay the RWC decreasing.2.Kleaf decreasing is not the trigger of gs and Pn decreasing,but it has the relationship with the RWC decreasing,and could regulated the speed of Pn decreasing.3.Modern cultivars could be recovered from the severity drought stress faster than landraces,this was benefit to drought adaption.The water use was not related with the threshold of SWC on gs decreasing,but had significant relationship with leaf mass(leaf area),the yield had negative relationship with water use under WS treatment,but no relationship between them when under well water condition(WW).4.Modern cultivars had higher yield under WS treatment most due to the higher and steady HI,smaller leaf area,as well as select big seed size,while the physical response was small effect on final yield determination in our study.5.When under water limited condition,the higher yield of soybean under filed condition also most due to the higher HI,while in higher precipitation condition,the higher yield rely on more biomass accumulation.Higher HI always connected with the less branches,closer to the determinate growth habitat,and big size(but never too large).However,those traits may not benefit to soybean yield performance when under more precipitation condition.6.Modern cultivars had higher leaf mass per area(LMA)than the landraces(2016R1:42.9 vs 34.0g/m2,R6:50.7 vs 40.0 g/m2;2017 R1:47.1 vs 38.2 g/m2,R6:56.7 vs42.9 g/m2),and water stress and progressive growth stage could increase the LMA in soybean,but no difference among different densities.The higher LMA would limit the leaf expanding,but delay the leaf dysfunction,improve water use efficiency.7.Modern cultivars had lower leaf area index(LAI)than the landraces when under certain plant density,this index could be influenced by water conditions,LMA,and plant density.According the relationship between the LAI and yield,there was parabolic curve,the vertical of the parabolic was the best LAI for yield harvest,and this vertical could be moved as the condition changed.People could regulate the LAI to the most adaptive value by change the soybean plant density.According to the results,we found the modern cultivars had more conserve water traits than the landraces,those traits including the gs,Kleaf parameter characterization response faster to the water stress on the stomatal level,as well as less biomass allocated to the branch,more clear of growth habitat,higher LMA and lower LAI,those traits may do not performance well when under high resource conditions,but they may be had better yield performance,and could be the reference to ideal traits for breeding in this area. |
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