| This study was carried out systematically research on the 12 introduced alfalfa varieties. The diurnal dynamics of photosynthetic rates (Pn) at different growth stages were studied, as well as photosynthesis and transpiration characteristics at the peak yield stage (4-7 years) of 12 alfalfa varieties. The changes of photosynthesis and transpiration were discussed at peak yield stage and the effective ways of using light and water were analysed to provide fundamental basis for high photosynthetic efficiency of plant breeding and reasonable cultivation of alfalfa. The results were as follows:1. The diurnal curves of net photosynthetic rate(Pn), transpiration rate(Tr)of alfalfa leaves had two peaks at regreening stage, but with only one peak at branching stage and budding stage.The two peaks at regreening stage occurred at 12:00 am and 14:00 pm and there was an obvious midday depression at 13:00 pm which was controlled by non-stomatal factor.The average value sequence of diurnal net photosynthetic rate(Pn) and transpiration rate(Tr) from high to low were:budding stage>branching stage>regreening stage and averages of diurnal water use efficiency(WUE)were:regreening stage>budding stage>branching stage, and averages of diurnal light use efficiency (LUE) were:regreening stage>branching stage>budding stage. So it can be inferred that alfalfa has higher photosynthetic capacity and more water needed at budding stage. The measures of cultivation and administration should be helpful to reduce the consumption of plant water transpiration and meet their water needs in summer. It is very limited for alfalfa to take advantage of photosynthetically active radiation. In case of the negative influence, we can breed the high light efficiency alfalfa variety in order to enhance its light use efficiency.2. The net photosynthetic rates of 4-year WL-525,Emperor,WL-232,WL-323 leaves were significantly higher than the other 8 varieties(P<0.05) and Pondus was the lowest. Pn of 5-year Queens 2000 leaves were significantly higher than the other varieties (P<0.05) and AmeriStand201 was the lowest. Pn of 6-year Emperor leaves was significantly higher than the other 11 varieties (P<0.05) and Phabulous was the lowest. Pn of 7-year Emperor leaves was significantly higher than the other 11 varieties (P<0.05) and Golden empress was the lowest.The transpiration rates of 4-yaer Emperor and Pondus leaves were significantly higher than the other varieties (P<0.05) and AmeriStand201 was the lowest. Tr of 5-year Queens 2000 leaves were significantly higher than the other varieties (P<0.05) and AmeriStand 201 was the lowest. Tr of 6-year Emperor leaves was significantly higher than the other varieties (P<0.05) and AmeriStand 201 was the lowest. Tr of Emperor and Queens 2000 leaves were significantly higher than the other varieties (P<0.05) and WL323 was the lowest. 4-year WL232,WL525,AmeriStand201,WL 414,WL 323 leaves had the significantly higher water use efficiency than the other varieties(P<0.05) and Pondus was the lowest. 5-year WL232,WL525,WL414 leaves had the significantly higher WUE than the other varieties(P<0.05) and Muzi 401 was the lowest. 6-year Golden empress leaves had the significantly higher WUE than the other varieties (P<0.05) and Pondus was the lowest. 7-year WL 323 leaves had the highest WUE and Muzi 401 was the lowest.Among the 4-year alfalfa varieties, WL-323 leaves had the highest light use efficiency and Victoria was the lowest. LUE of 5-year WL-232 and Emperor leaves were significantly higher than the other varieties (P<0.05) and Muzi 401 was the lowest. 6-year WL-232 leaves had the highest LUE and Phabulous was the lowest. Among the 7-year alfalfa varieties, Emperor leaves had the highest LUE and Victoria was the lowest.3. Emperor showed the highest photosynthetic capacity while its transpiration capacity was vigorous too. It showed higher advantageous function than the other alfalfa varieties. Correlation analyses results well-explained how Pn and Tr are affected by those factors according to their contribution extent. There was a significant positive correlation between Pn, PAR and Gs, and PAR played a more important role than Gs. There was an extremely significant positive correlation between Tr, PAR and Gs and a significant positive correlation between Tr and Ta. Tr and Ci showed a significant negative correlation. The factors that affecting Tr of Emperor could b e ranked from high to the low as PAR > Gs> Ta> Ta> Ci. |
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