Screening For High Water Use Efficiency Of Switchgrass (Panicum Virgatum L.) And Study On Its Mechanism Under Cadmium Stress

With the development of industrialization and urbanization,the soil of cadmium pollution is more and more serious.Cd stress can lead to water stress during the process of plant growth and influence the water absorbing of plants,generally decrease the plant photosynthesis and transpiration rate,which results in the decrease of plant water use efficiency(WUE).Switchgrass(Panicum virgatum L.)is a C4 perennial grass,adaptable to wide range of ecosystems as well as marginal lands,arid and semi-arid areas.It has high biological yield and energy conversion rate and has been assessed as the most potential energy grass by the U.S.Department of energy.Low per capita arable land and water shortage are the key factors that restrict the development of Chinse agriculture.Based on the development of bioenergy,the situation should not be related to grain feeding,so it is very important to select the energy plants suitable for the marginal and polluted soil which has high water use efficiency.In this experiment,14 cultivars of switchgrass with high biomass were selected under hydroponic condition treated with 0(control)and 10?mol L-1 CdC12·2.5H2O.Calculating WUE and RWUE(Relative water use efficiency)according to Pn and E by measuring the photosynthetic parameters under cadmium stress.Then 6 cultivars of switchgrass with different WUE were selected to verify under soil culture.Meanwhile,the intrinsic mechanism of the differences was further explored.The results were as below:1.Compared to the control,the WUE of 14 switchgrass cultivars were significantly reduced under Cd stress,and lowland types of which were significantly higher than upland types.The highest was Kanlow and lowest was Cave in Rock.And the WUE and RWUE of Kanlow were twice than Cave-in Rock.The 14 switchgrass cultivars were divided into 3 RWUE types by cluster analysis.Three(Alamo,BoMaster and Kanlow)were high RWUE types,six(Blackwell,Carthage,Dacotah,Shelter,Shawnee and Trailblazer)were medium RWUE types and five(Cave in Rock,Forestburg,Longisland,New York and Sunburst)were low RWUE types.Combined with the Cd absorption of switchgrass,our results demonstrated that the high cadmium-tolerance cultivar had a strong ability to accumulate cadmium.2.Under soil conditions,the WUE of different switchgrass cultivars was also inhibited by cadmium stress,the highest was Kanlow and the lowest was Cave in Rock,and the lowland types was generally higher than that of upland types.The results were in agreement with the hydroponic screening,which proved the reliability of the screening results under hydroponic culture.3.That in-depth study of the mechanism showed that different varieties of switchgrass under cadmium stress had different WUE.The content of chlorophyll and trace elements were higher in high WUE cultivars,showed high photosynthetic performance and low leaf water loss rate.The mechanism of physiological was maybe related to ABA level,high WUE cultivars had high ABA contents and lowland types was higher than the upland types.As for molecular aspects,the relative expression of stomatal related genes ERECTA,EPF1 and aquaporin PIP1 showed that high WUE was significantly higher than low WUE of switchgrass.The combined contribution of stomatal control and water uptake were responsible for the diversity of WUE in switchgrass.The research screened out the high WUE switchgrass cultivar under Cd stress and provided a theoretical basis for using genetic engineering means to find and innovate high WUE of switchgrass.