不同土壤水分对向日葵光合光响应的影响

以食用向日葵为试验材料，大田试验采取人为控制土壤水分在胁迫、适宜和过湿 (土壤田间持水量的40%~54.9%，55%~69.9%和70%~90%) 条件下，研究了向日葵3个生育期 (二对真叶—花序形成期、花序形成—开花期、开花—成熟期) 的光合光响应特性。结果表明:在试验设置光强条件下，各生育期净光合速率随着光合有效辐射的增加而增加，同等的光合有效辐射下净光合速率也随着土壤水分的减少依次降低，尤其是随着光合有效辐射的增大愈加明显。土壤湿度对最大净光合速率和表观量子效率的影响并不是同步的，最大净光合速率随着土壤湿度的增加而增大，而表观量子效率在一定程度的水分胁迫情况下出现最大值。不同的土壤水分含量对光补偿点和光饱和点影响不同，光饱和点随着土壤水分的增加而增加，光补偿点却相反，表明水分胁迫使向日葵可利用光的范围缩小，而适宜水分则扩大了光的利用范围，更有利于干物质积累。暗呼吸速率随着植物的生长进程逐渐降低，不同生育期的水分胁迫均导致暗呼吸速率降低。

Effects of Different Soil Moistures on Photosynthetic Characteristics of Sunflower

The soil drought is one of key factors limiting photosynthesis in northwest areas of China. In order to understand the influence of drought stress on crop, the light response curves and several parameters of photosynthesis of sunflower are measured with Li-6400 Portable Photosynthesis System under three soil moisture grades: Arid soil, suitable soil moisture and wetter soil moisture (corresponding soil water contents are 40%-54.9%, 55%-69.9% and 70%-90%, respectively) in different development stages (two pairs of leaves-bud stage, bud stage-flowering stage, flowering stage-maturity stage). Results show that all coefficients of light response curve equations fitted using rectangular hyperbola model are above 0.99, meaning good compatibility between the model and the response process of photosynthesis of sunflower to light. The light response curves of sunflower growing under different soil moisture in different development stages show similar trends, the net photosynthetic rate (P_n) increases with photosynthetic active radiation rapidly at first and then slowly. For different development stages, changes of light response curves show a similar regulation with reduced soil moisture, but P_n of sunflower under wetter soil moisture is greater than that under suitable soil moisture and drought stress at the same photosynthetic active radiation, and differences are statistically significant with the photosynthetic active radiation increasing. Influences of soil moisture on the maximum net photosynthetic rate (P_max) and apparent quantum efficiency are not synchronous. P_max increases with soil moisture and apparent quantum efficiency under the condition of water stress in maximum. In the entire growth period of sunflower in the Hetao Irrigation District, light compensation point and light saturation point are 30.51-107.98 μmol·m-2·s-1 and 2260.8-3658.9 μmol·m-2·s-1, respectively. It shows that sunflower with high solar energy utilization efficiency is the typical sun plants, and is particularly fond of light. The effect of soil moisture content in light compensation point and light saturation point is different. The light saturation point increases with soil moisture, while light compensation point is the opposite. According to the variation of light compensation point and light saturation point, sunflower under suitable soil moisture not only expands the scope of the use of light but also is conducive to the accumulation of dry matter, sunflower under drought stress narrows the range of available light. The dark respiration rate (R_d) decreases gradually with plant growth, and decreases under drought stress in different development stages, which is conducive to reduce the influence of drought stress on dry matter accumulation of crops.