土壤含水量对条墩桑光合特性及水分利用效率的影响

条墩桑是条叶兼用的一种优良灌木桑,可用于干旱半干旱地区的风沙治理。以2年生条墩桑幼苗为试验材料,采用盆栽控水法,研究了水分胁迫下条墩桑光合特征及其水分利用效率的变化。不同土壤水分状况下,条墩桑净光合速率日变化曲线基本呈"双峰"型:正常水分和轻度干旱条件下,净光合速率在上午11:00达到最大值,分别为17.55和15.20μmol/(m2·s);中度干旱条件下,净光合速率在上午10:00前后就达到峰值,为9.60μmol/(m2·s),光合午休相对提前了1h且时间延长,其净光合速率与气孔导度的下降平行进行。水分利用效率最高值出现在上午较早时分,且上午的水分利用效率明显高于下午,其日平均值下降幅度明显小于净光合速率的降低幅度。净光合速率下降的原因既有气孔限制,又有非气孔限制因素,随着土壤水分含量的减少,非气孔限制因素作用增加。

Characteristics of Photosynthesis and Water Utilization Efficiency of Cluster Mulberry Under Different Soil Moisture Conditions

Cluster mulberry is an excellent shrub, which is important in controlling desertified sandy land in arid and semi-arid areas. Photosynthetic characters and water utilization efficiency of cluster mulberry with two-year-old pot-cultured grafting seedlings under 3 kinds of soil moisture conditions were investigated in this paper. The experiment results showed that the diurnal course of net photosynthetic rate (Pn) displayed a two-peak pattern under different soil moisture conditions. Under the normal soil moisture and light drought conditions, the peak value were 17.55 and 15.20 μmol/(m2·s), respectively, which occurred at 11∶00 o'clock. Under the middle drought condition, the peak value was 9.60 μmol/(m2·s), which appeared at 10∶00 o′clock, and the mid-day depression in net photosynthesis started ahead of 1 hour and its duration was longer, both Pn and stomatal conductance (Sc) were decreased. Water utilization efficiency (WUE) culminated in the early morning, WUE in the forenoon was higher than that in the afternoon, and the decrease in daily mean of WUE was less than that of Pn. Whether the stomatal factor acted as limiting factor for photosynthesis depended on the conditions of soil moisture content. While the soil moisture content reduced, the role of non-stomatal limitation increased.