The Water Demand Charactreristics During Seedling Establishment And Water Ecological Adaptability At Seedling Stage Of Switchgrass

Water deficit is one of major limiting factors for crops growth and development in aridand semi-arid areas, it severely affect a series of seed germination, and physiologicalprocesses of plant, drastically restrict the formation of production. In dry conditions, how toensure the seed germination and the water ecological adaptability at seedling stage become anurgent problem. The hydroponic (drought stress simulated by PEG-6000) and pottedexperiments (controlling soil moisture) were designed in Switchgrass(Panicumvirgatum L.)Pathfinder, Traiblazer and Alamo to study seed germination and the water physiologicalecology characteristics and drought tolerance of switchgrass including the seed germinationcharacteristics, seedling establishment and water ecological adaptability in switchgrass underdrought stress,.The major results are as follows:1、both4℃low temperature freezing treatment and8M sulfuric acid treatment canenhance the Germination Ratio, Germination Index and Vigor Index, and can reduce theRadicle／Embryo Ratio. The effect of4℃low temperature freezing treatment is better than8M sulfuric acid treatment compared with control under normal water supply, showing that,Germination Ratio of Pathfinder, Traiblazer and Alamo seeds increased13.5%,10.6%and8.8%respectively; Germination Index of Pathfinder, Traiblazer and Alamo seeds increased30.0%,27.8%and9.6%respectively; and Vigor Index of Pathfinder, Traiblazer and Alamoseeds increased37.3%,45.7%and17.9%respectively. The seed germination characteristicsdiffered significantly among Pathfinder, Traiblazer and Alamo under the same treatment.Pathfinder seed had the highest germination capability among three species seeds and thegermination capability of Alamo was the lowest. Seed germination capability differed indifferent PEG concentrations, showing that Germination Ratio, Germination Index and VigorIndex decreased with increasing PEG concentration; but Radicle／Embryo Ratio increasedwith increasing PEG concentration. In addition, the concentration of PEG, which reached-0.3MPa, was the threshold for showing effects of drought on the germination traits ofswitchgrass in our research. 2、with the decrease of water potential, it must take more time to finish50%seeds radicalemergence, plumule emergence and seedling establishment than control group, and thewater-requirement threshold of each phase is different, the critical water potential at50%switchgrass seedlings establishment stage was higher than those at radical emergence andplumule emergence stage. It indicated that the stage of seedlings establishment was the mostsensitive to water environment, the ability to tolerate stress and the drought resistance wasminimal. Under different treatments, by contrast, in the same species,4℃low temperaturefreezing seeds treatment, the time was shortest of seeds radical emergence, plumuleemergence and seedling establishment and the water-requirement threshold in different stagewas maximum. On the other hand, under the same processing method, the enduring capabilityto water stress of Pathfinder was less affected than Trailblazer and Alamo. Therefore,4℃low temperature freezing seeds treatment has best effects, Pathfinder has strongest and mostenduring capability and drought resistance.3、Water stress obviously affect the growth of switchgrass, Trailblazer plant highperformance for: moderate water stress treatment (MS) slightly higher than the normal watertreatment (CK) and lowest in severe water stress treatment (SS), Pathfinder plant highperformance for: CK> MS> SS. Under normal water processing, the Pathfinder plant ishigher than Trailblazer; Under SS treatment, the Trailblazer plant high slightly higher thanPathfinder. Under different water processing, the stem diameter characteristic of Trailblazerand Pathfinder performance for: CK> MS> SS. Among them, CK treatment plant stemdiameter and SS treatment plant stem diameter has significant differences.4、 Switchgrass Trailblazer and Pathfinder under water stress treatment leaf netphotosynthetic rate (Pn) and stomatal conductance (Gs) are reduced with the increase of stresslevel. Switchgrass Trailblazer intercellular CO2(Ci) is reduced with the stress degreeincreased, under SS treatment, the Tr is lower; Under MS treatment, Switchgrass Pathfinderhas a lowest Ci and a highest Tr, but no significant difference between the treatments. Forswitchgrass Trailblazer, under SS treatment, the leaf Gs is reduced, the Ci concentration isdecreased, and the Ls is increased, which indicated the reduction of Pn is mainly resultedfrom stomatal limitation; For switchgrass Pathfinder, under MS treatment, the leaf Gs isreduced, while the Ci is decreased and the Ls is increased, stomatal limitation is the maincause, under SS treatment, leaf Gs is reduced, the Ci concentration is increased, the Ls isdecreased, which suggested that the decrease of Pn is mainly attributed to the decline ofdiachyma cells photosynthetic activity, namely, the non-stomatal limitation; Visible, with theincrease of stress, switchgrass Trailblazer photosynthetic capacity is mainly stomatallimitation, and switchgrass Pathfinder decline of photosynthetic capacity has a variational process of from stomatal limitation to the non-stomatal limitation with the drying of soil.The chlorophyll content of switchgrass Trailblazer has a little change under the threewater treatment; For switchgrass Pathfinder, chlorophyll content increased before they arereduced, which indicated that the chlorophyll is destroyed, free radicals accumulation inplants and the chloroplast membrane peroxidation, damage the chloroplast structure andfunction, make the chlorophyll degradation under the stress. Under CK treatment and MStreatment, switchgrass Pathfinder of chlorophyll content slightly higher than the switchgrassTrailblazer, under SS treatment, switchgrass Trailblazer chlorophyll content is higher.