西北旱区不同灌水下限对紫花苜蓿生长与光合特征的影响

为了揭示西北干旱气候条件下不同灌水下限对紫花苜蓿光合日变化特征及生长的影响,设置了3个灌溉处理(T1:80%田间持水量,T2:60%田间持水量,T3:40%田间持水量。田间持水量,Field capacity,FC),并测定各处理紫花苜蓿不同生育时期叶片的光合特征和生长指标。结果表明,紫花苜蓿的株高和茎粗随灌水量的降低而减小。各处理在不同生育时期的净光合速率(Pn)、蒸腾速率(Tr)日变化趋势相似。其中7:30~9:30呈上升趋势,T1、T2变化幅度高于T3;9:30~13:30呈下降趋势,T3下降幅度较大。不同生育期中,分枝期的Pn、Tr、叶片水分利用效率(WUE)及光能利用率(LUE)最高,且T1、T2的光合特征显著高于T3(P<0.05)。这表明适当的灌水量可达到增强紫花苜蓿光合作用和叶片生长的效果,且随着生育时期的改变,导致Pn下降的原因由气孔因素转变为非气孔因素。在水分胁迫加剧的情况下,Pn下降的非气孔因素影响更加明显。

Effects of Different Irrigation Limits on Growth and Photosynthetic Characteristics of Alfalfa in Arid Region of Northwest China

To reveal the effects of different irrigation limits on the diurnal photosynthetic characteristics and growth of alfalfa in arid climate of Northwest China,three irrigation treatments were set up(T1,80%FC;T2,60%FC;T3,40%FC.FC,field capacity),in which the photosynthetic characteristics and growth indexes of alfalfa leaves at different growth stages were measured.The results showed that the plant height and stem diameter of alfalfa decreased with the reduction of irrigation.The diurnal variation trends of net photosynthetic rate(Pn)and transpiration rate(Tr)of all treatments was similar at different growth stages.From 7:30 to 9:30,an upward trend of Pn and Tr was shown that the increase in T1 and T2 treatments was higher than that in T3 treatment.From 9:30 to 13:30,a downward trend of Pn and Tr was shown that T3 had the greatest reduction.Among different growth stages,Pn,Tr,leaf water use efficiency(WUE)and light energy utilization rate(LUE)were the highest in branching stage,in which the photosynthetic characteristics of T1 and T2 were significantly higher than that of T3(P<0.05).This implied that proper irrigation could achieve the effect of enhancing photosynthesis and leaf growth of alfalfa.With the change of growth stage,the cause of Pn decline changed from stomatal factors to non-stomatal factors.Under the severe water stress conditions,the non-stomatal factors of Pn decrease were more obvious.