Abstract: The efficient use of the soil water by the deep and wide-distributed root system of alfalfa(Medicago sativa L.) accounts for its outstanding adaptation and wide distribution in the world.Whereas,it is difficult to sample and examine the root water use behavior due to the rooting depth in the soil layer.Realization of water stress at different degrees by cutting the root at different depth could provide important evidences for the relationship between the root and the shoot and leaves.A study was conducted to investigate the effect of the root pruning at the depth of the 40 cm,80 cm,120 cm,160 cm,200 cm,240 cm,280 cm,320 cm,360 cm,400 cm,450 cm and 500 cm on the leaf relative water content(RWC) at the branching stage and the activities of leaf SOD,POD and CAT at the branching,budding and initial blooming stages in the first harvest.Alfalfa without root pruning was taken as the control.The results show that leaf RWC of all treatments was lower than that of the control and RWC of the pruning treatments shallower than 280 cm were significantly lower than those of other treatments at 0.05 probability level.The effect of root pruning on the antioxidant enzyme activities varied among the root-cutting depths and the growth stages.Generally,the root pruning decreased the SOD,CAT activities and increased the POD activity at the branching stage.Furthermore,the difference of the CAT activity of the all treatments and the POD of the treatments shallower than 200 cm was significant at 0.05 level.However,the three enzyme activities of all treatments were lower at the budding and the initial blooming stages than those of the control and the differences of SOD and POD activities were significant at 0.05 level.At the same time,the SOD and POD activities of the treatments of shallower than 160 cm and deeper than 400 cm were significantly higher than those of other treatments.As a whole,the activities of the antioxidant enzymes tended to decrease under the water stress caused by the root pruning.

Key words: Alfalfa, Root pruning, Antioxidant enzyme

摘要： 发达的根系可以使紫花苜蓿(Medicago Sativa L.)充分利用土壤水分,这是其适应性强和分布广的重要原因,但由于根系入土深而取样和观察困难,所以研究起来具有一定的难度。在不同深度断根后形成吸水胁迫,可为研究不同深度的根系对土壤水分的吸收利用提供一定的理论依据。为此,于紫花苜蓿返青期,分别在距地面40 cm、80 cm、120 cm、160 cm、200 cm、240 cm、280 cm、320 cm、360 cm、400 cm、450 cm和500 cm土层处水平切断其根系,研究断根对第1茬紫花苜蓿分枝期、现蕾期和初花期叶片中叶片相对含水量(RWC)、超氧化物歧化酶(SOD)、过氧化物酶(POD)、过氧化氢酶(CAT)活性的影响。结果表明:不同深度断根均可使紫花苜蓿叶片中RWC降低,且240 cm以内的断根处理RWC显著(P<0.05)降低;断根对叶片中保护酶活性的影响因生育期和断根深度而异,断根后,分枝期叶片中SOD、CAT活性绝大多数处理升高,其中,CAT活性差异达显著水平(P<0.05),而POD活性绝大多数处理降低,且200 cm以内断根的处理差异达显著水平(P<0.05);现蕾期和初花期叶片中各保护酶活性均降低,SOD、POD活性绝大多数差异达显著水平(P<0.05),且在≤160 cm的浅层断根和≥400 cm的深层断根叶片中各保护酶活性显著(P<0.05)较中间深度断根的高;断根形成水分胁迫后,保护酶活性呈降低趋势。

关键词: 紫花苜蓿, 断根, 保护酶