| In order to quest pasture's water physiology and photosynthetic physiology characteristics, supply theoretical principle and reference to dry areas'hayland, using physiological ecology and photosynthesis,transpiration survey technique , test the four pastures'annual plant: Astragalus adsurgens Pall. Melilotus suaveolens Ledeb. Medicago sativa L. Onobrychis viciaefolia Scop., to survey and evaluate the diurnal fluctuation and response characteristics of four pastures'grow,water physiology,photosynthesis,transpiration. Analyze the four pastures'variation tendency of water physiology characteristics, Analyze the four pastures'photosynthesis and transpiration diurnal fluctuation, Analyze the four pastures'photoresponse characteristics,fitting and photoresponse's subthreshold response, definite the pertinency among four pastures'Pn Tr WUE LUE and environmental factors, conclusion as follow:1. Analyze the four pastures'characteristics about growthThe grow situation of the four pastures as follow: Melilotus suaveolens Ledeb.>Medicago sativa L.>Astragalus adsurgens Pall.>Onobrychis viciaefolia Scop.。Melilotus suaveolens Ledeb.'s average stem length is the highest one is 43.73cm,the lowest one is Onobrychis viciaefolia Scop., Arrange: Melilotus suaveolens Ledeb.>Medicago sativa L. > Astragalus adsurgens Pall. > Onobrychis viciaefolia Scop.; Astragalus adsurgens Pall.'s average lamina length is the longest one, is 2.68cm,the smallest one is Medicago sativa L.,is1.45cm Arrange: Melilotus suaveolens Ledeb.>Astragalus adsurgens Pall.>Medicago sativa L.>Onobrychis viciaefolia Scop.; Arrange of average lamina width: Melilotus suaveolens Ledeb.>Astragalus adsurgens Pall.>Medicago sativa L.>Onobrychis viciaefolia Scop., the widest one is 1.08cm,the narrowest one is 0.82cm; Arrange of average ramose quantity: Melilotus suaveolens Ledeb.>Medicago sativa L.>Onobrychis viciaefolia Scop.>Astragalus adsurgens Pall., the maximum one is 12.75,the leastone is 7.80; Arrange of root/shoot ratio: Medicago sativa L. > Onobrychis viciaefolia Scop. > Astragalus adsurgens Pall > Melilotus suaveolens Ledeb., the bigest one is 0.995,the leastone is 0.38.2. Make clear the four pastures'characteristic of water physiology(1) The variation tendency of saturation moisture content is similar to leaf water potential, to lower along with the reducing of soil moisture content, tendency will slow down over time, the variation is not obvious under low soil moisture content. Compare with the four pastures, Melilotus suaveolens Ledeb.'s leaf water potential is influenced seriously by soil moisture content.(2) The four pastures'free water,bound water,WSD,leaf water potential are affected by soil moisture content obviously, the correlation among them is obvious, but is different between different breeds. Along with the reducing of soil moisture content, the variation tendency of the four pastures'free water is similar, all of their variation tendency register as increased at first, then decreased; the variation tendencies of the four pastures'bound water,WSD and bound water to free water are opposite to free water.(3) The four pastures'leaf water potential reduces as the soil moisture content's reducing, when soil moisture content reduce to field water capacity's 30%,all the pastures'leaf water potential will be undulate except Onobrychis viciaefolia Scop., then will be larger speedy and adience to 0,the three pastures will be wilting, if watering again, it will lose plant.3. Expound the diurnal fluctuation characteristics of the four pastures'photosynthesis and transpiration parametersThe four pastures'photosynthesis and transpiration parameters will increased at first, then decreased as the moisture content's reducing, under serious water stress, Pn's curved shape will be two-humped, WUE's curved shape will be singlet, Tr's curved shape will be shape of U ,Gs's curved shape will be shape of V, the factor which lead Ci to a low level is stomatal limiting factor.4. Explain clearly soil moisture content suitability and moisture using of the four pastures in photosynthesis processAs the reducing of soil moisture content, all of the four pastures'WUE register as ascendant trend, this explain that the water utilization efficiency of the four pastures will increase under soil moisture stress, this can explain the four pastures'capability of anti-drought.5.Discourse the characteristics of photoresponse, definite the model of photoresponse(1) The four pastures have the capability to endure excellent illumination, they have upper Pn and WUE under excellent illumination. The four pastures has strong adaptability to light, when PFD is between 800 and 1600μmol·m-2·s-1 the Melilotus suaveolens Ledeb. has high-level photosynthesis rate, when PFD is between 600 and 1600μmol·m-2·s-1 the Astragalus adsurgens Pall.and Medicago sativa L. both has high-level photosynthesis rate, when PFD was between 400 and 1600μmol·m-2·s-1 the Onobrychis viciaefolia Scop. has high-level photosynthesis rate.(2)The optimum model of photoresponse for the four pastures is the index model, it is outgo to the other model, while, it is unacted on soil moisture content. Pnmax,LCP,LSP and Rd are close to measured value.6. Analyze the corelation among the four pastures'photosynthesis,transpiration, WUE,LUE to environmental factorUnder condition of high soil moisture content(more than 60% of field water capacity), factors of determination to photosynthesis,transpiration,WUE,LUE are PFD,Gs,Ls ,limiting factor to them are Tc,Ci ; under condition of low soil moisture content(less than 40% of field water capacity), factors of determination to photosynthesis,transpiration,WUE,LUE are PFD,Gs,Ls ,to them are Tc,Ci,Tl. In serious soil moisture stress cases, plant closes cell to reduce moisture dissipation, in the same time, limiting the action to lower lamina temperature by transpiration, lamina temperature'arising touch enzyme activity lamina inside, for this reason, lamina's temperature influence the change of photosynthesis,transpiration,WUE,LUE.
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