干旱对番茄幼苗光合和某些生理指标的影响

干旱缺水已成为植物光合作用和生长发育主要的限制因素,在干旱胁迫下,作物的生长发育受到影响,依据作物的形态变化进行浇灌属于延后性灌溉,未必能完全补偿对作物生长造成的影响。确定灌溉时间点,既确保植物正常生长不受影响,也可以提高水分利用效率,减少水资源浪费,从而达到节水灌溉的目的。该研究以温室土槽栽培番茄幼苗为材料,设定土壤含水量为30.00%(对照)、21.00%、18.00%、15.00%、12.00%、9.00%,研究了干旱胁迫对番茄叶片光合特性、抗氧化酶(超氧化物歧化酶、过氧化物酶、过氧化氢酶)、碳酸酐酶活性变化的影响,并以此表征番茄幼苗需水信息。结果表明:随着干旱胁迫程度的增加,叶片水势逐渐降低。超氧化物歧化酶、过氧化物酶及过氧化氢酶等抗氧化酶在番茄幼苗耐受水分胁迫中起到重要的作用;超氧化物歧化酶、过氧化物酶在干旱胁迫条件下反应更迅速,但过氧化氢酶相对于超氧化物歧化酶、过氧化物酶对干旱胁迫的耐受能力更强;干旱胁迫条件下抗氧化酶活性的转折点在15.00%土壤含水量左右;水分胁迫条件下碳酸酐酶参与了对光合作用的调节,并在15.00%土壤含水量时活性升至最高,使得番茄仍能维持较高的光合速率,以维持正常的生理机能;随着干旱胁迫程度的加剧(12.00%土壤含水量),碳酸酐酶活性与净光合速率都迅速下降。综上分析,当土壤含水量低于15.00%并高于12.00%时,对作物进行灌溉最为合适。抗氧化酶及碳酸酐酶活性可为作物最佳灌溉时间点的预测提供科学依据。

Effects of drought on photosynthesis and the physiological indices in tomato

Under drought stress, the crop growth and development are affected significantly. The irrigation based on the changes of morphology, which has lag, may not be able to completely offset the inhibitory effect of plant growth caused by drought stress. Determining the irrigation time can ensure normal growth of plants, improve water use efficiency, reduce the waste of water resources, and achieve the goal of water-saving irrigation, eventually. Tomato seedlings cultivated in soil bin of greenhouse were selected as experimental material. The soil water content was set at 30.00%(the control), 21.00%, 18.00%, 15.00%, 12.00% and 9.00%, respectively. Photosynthetic parameters, such as net photosynthetic rate, transpiration, stomatal conductance, and intercellular CO₂ concentration, were measured using a portable LI-6400XT photosynthesis system. The water potential, the activities of antioxidant enzymes(superoxide dismutase, peroxidase, catalase)and carbonic anhydras, and the content of malondialdehyde in tomato leaves were determined, simultaneously. The influences of drought stress on the activities of antioxidant enzymes, carbonic anhydrase, and photosynthetic characteristics in tomato leaves were studied. These indexes were used to characterize the water requirement information of tomato seedling. The results showed that leaf water potential decreased gradually with the increase of drought stress. The decrease in water potential of tomato leaves was insignificant when the soil water content was more than 15.00%. However, compared with the control, the decrease was significant when the soil water content was less than 12.00%. The drought stress inhibited the photosynthesis. But the net photosynthetic rate had a rebound when the soil water content was 15.00%. Antioxidant enzymes such as superoxide dismutase, peroxidase and catalase played important roles in drought-resistant process of tomato seedlings. Superoxide dismutase and peroxidase had more swift response than catalase under drought stress. Compared with superoxide dismutase and peroxidase, catalase had stronger tolerance to drought stress. The turning point of soil water content responded to drought stress conditions, which affected the activity of antioxidant enzyme, was at about 15.00%. The content of malondialdehyde in tomato leaves increased with the increase of drought stress. The activity of carbonic anhydrase was the highest when soil water content was 15.00%. At this time, carbonic anhydrase can provide enough water and carbon dioxide for photosynthetic organs through the conversion of bicarbonate, which ensured plants could maintain high photosynthetic rate and normal physiological function. Both carbonic anhydrase and photosynthetic rate decreased sharply with the persistent increase of drought stress(less than 12.00% soil water content). At this time, carbonic anhydrase in tomato leaves was not competent in regulating water status, and the photosynthesis declined rapidly. Therefore, we suggested that carbonic anhydrase in tomato leaves participated in the regulation of the photosynthesis under the drought stress. Concluded from above, it was better to irrigate the crop when the soil water content was lower than 15.00% and higher than 12.00%. The activities of superoxide dismutase, peroxidase, catalase and carbonic anhydrase in leaves would provide a general consideration for predicting the best irrigation time for crops.