夏大豆叶片光合作用与光强的关系

Relationship between Photosynthetic Rate and Light Intensity in Summer Soybean

以12个生育期和结荚习性不同的夏大豆品种(系)为材料,测定其在不同条件下青壮龄(展开13日龄)叶片和幼龄(展开4日龄)叶片的光合速率。结果表明,在晴天、适宜供水和自然光照下,夏大豆青壮龄叶片的光合速率(y)与光强(x)呈极密切的正指数曲线关系x=aeby,光合速率随光强增强而升高,没有“午休”现象。幼龄叶片在低光强下,光合速率随光强增强而升高;当光强增加到500μmol.m-2.s-1左右时,光合速率不再增加,呈现光饱和现象。缺水使夏大豆叶片的光合速率降低,严重缺水时出现“午休”现象。严重缺水是自然光照条件下大豆光合速率降低的主要原因之一。

Soybean [ Glycine max （L.） Merr. ] is a C3 species with low photosynthetic rate and low photo saturation point,and has Noontime Snooze of photosynthesis. It was suggested that higher light intensity was the main reason that caused photosynthetic rate decline and Noontime Snooze of photosynthesis in soybean. Photosynthetic rate of mature （fully expanded for 13 days） leaves of summer soybean cultivars Ludou 4 were measured in clear day, under suitable water supply and natural light condition in 1991, 1993, and 1997. A positive exponential correlation （ x =αe^by ） between Photosynthetic Rate （y） and Sunlight Intensity （x） was observed in mature leaves of Ludou 4, and Noontime Snooze was not observed （Fig. 1）. Under the same conditions, photosynthetic rate of young leaves （fully expanded for 4 days） of summer soybean cultivars（Ludou 4, Ludou 6, Ludou 11, Ludou 12, Qifeng 84, Qifeng 850, Qifeng 918 and 7517-88） was increased with the increase of sunlight intensity when sunlight intensity was lower than 500 μmol·m^-2·s^-1 , and photosaturation of photosynthesis was observed as sunlight intensity reached 500μmol·m^-2·s^-1 （ Fig. 2）. Photosynthetic rate of mature leaves of 12 summer soybean cultivars was measured under different water supply condition （ amount of supplied water was 72.8 kg·m^-2 , 122.8 kg·m^-2 , 152.8 kg·m^-2 , 182.8 kg·m^-2 , 242.8 kg·m^-2 , 422.8kg·m^-2 from emerge to initial flowering stage） in 1991 and 1992. The results showed that photosynthetic rate of summer soybean markedly declined and Noontime Snooze was observed under the stress of drought and water logging. 182.8 kg·m^-2 was the best suitable water supply amount. The photosynthetic rate was decreased by 74.0% - 81.1% in 72.8 kg·m^-2 treatment, and by 29.9% - 38.6% in 422.8kg·m^-2 treatment as compared with that in the treatment of 182.8kg·m^-2（Table 1 ）. Under stress of serious drought （72.8 kg·m^-2 ）, photosynthetic rate slowly increased with increase of sunlight intensity when sunlight intensity waslow, but rapidly decreased when sunlight intensity was higher, and Noontime Snooze of photosynthesis was markedly observed in clear morning（ Table 2 and Table 3）. Drought was one of the main reasons that caused photosynthetic rate decrease.