| Photosynthesis is the basis of the yield formation. Studying the photosynthetic characters of different alfalfa varities in natural field can not only give a better appreciation of the whole recognition on its physiological characters, the ecological adaptation and the production potentiality, but also give out theory about developing high-yield, high-quality cultivation.7 alfalfa varieties including Ameristand201+ Z, Zhonglan No.1, Affiniy + Z, Xinjiangdaye, AmriGraze401+ Z, Lobo, and 13 R Supreme were used as materials to study the photosynthesis of alfalfa with Licor-6400 in the sixth year after being planted. On the nature sunshine condition, the Diurnal Variation of the photosynthetic rate (Pn) and the effects of environmental factors on it were studied under different growth periods and stubbles. The responses of photosynthetic rate to light intensity and CO2 concentration under different growed periods were measured and some characteristic parameters were calculated. The relations between chlorophyall contents, specific leaf weight (SLW) and Pn under different growth periods were also been studied. Then the general and specific characters of photosynthesis among different varieties of alfalfa were analysed and compared, and the rules of photosynthesis of different varieties under natural condition were explored. The photosynthetic characteristics of alfalfa had been comprehensively studied in this experiment, and what the results indicated are as follows:1. The diurnal changes of Pn in different alfalfa varieties presented multi-tendencies in 3 growth periods and 3 stubbles, such as"single peak""double peaks"curves and so on. Those types of curves differed with different varieties, growth periods and ecological factors. The Midday Depression of photosynthesis was regulated by both stomatal and non - stomatal limitation.2. The environmental factors had obvious effect on photosynthesis in alfalfa leaves. PAR and Cond were major elements influencing diurnal changes of Pn.3. Exponential equation and polynomial equation were fitted for those responses of photosynthetic rate to light intensity and CO2 concentration, and some characteristic parameters calculated from those equations were found to differ significantly among different varieties or different growth periods.4. The light compensation points(LCP) and the light estimate points(Lk) of alfalfa were respectively between 24~70μmol·m-2·s-1 and between 495~892μmol·m-2·s-1, thereamong , Zhonglan No.1 and Lobo possessed higher synthetic efficiency to weak light as they had lower LCP while Xinjiangdaye, 13 R Supreme and Ameristand201+ Z possessed higher synthetic efficiency to strong light as they had higher LSP. The CO2 compensation points(CCP) and the CO2 saturation points(CSP) of alfalfa were respectively between 49~160μmol·mol -1 and between 414~2313μmol·mol-1.The apparent quantum yield (AQY) and carhoxying efficiency (CE )were respectively between 0.036~0.065CO2·photon-1 and between 0.039~0.193μmol·m-2·s-1. 13 R Supreme, Lobo, Ameristand201+ Z and Xinjiangdaye are varieties with high photosynthetic efficiency as they displayed higher light utilization efficiency, higher photosynthetic potential and higher utilization of strong light as well as they demanded for higher light intensity. Different alfalfa varieties demanded for different light intensity, which may due to their differences of organization structure and physiological function of their leaves.5. Average of diurnal Pn in alfalfa leaves had very significant positive correlations with chlorophyall a (Chla) and SLW at brangching stage while they had insignificant correlations both at buding stage and flowering stage. Average of diurnal Pn in Lobo leaves had significant positive correlations with total Chl content among different growth periods, while they all presented insignificant correlations in other varieties'leaves.
|
PDF Full Text Request