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土壤有效磷(P)含量低是限制植物生长的主要因素之一。根形态变化和根系大量分泌以柠檬酸为主的有机酸是植物适应土壤P素缺乏的重要机制。以广泛分布于我国北方的重要豆科牧草黄花苜蓿(Medicago falcata)和豆科模式植物蒺藜苜蓿(M.truncatula)为材料,采用砂培方法,研究了低P胁迫对其植株生长、根系形态和柠檬酸分泌的影响,对比了两种苜蓿适应低P胁迫的不同策略。结果表明:1)低P处理显著抑制了蒺藜苜蓿与黄花苜蓿的地上部生长,而对地下部生长影响较小,从而导致根冠比增加。2)低P胁迫显著降低黄花苜蓿的总根长和侧根长,而对蒺藜苜蓿的上述根系形态指标没有显著影响。3)低P胁迫促进两种苜蓿根系的柠檬酸分泌,无论是在正常供P还是低P胁迫条件下,黄花苜蓿根系分泌柠檬酸量显著高于蒺藜苜蓿根系。上述结果表明,黄花苜蓿和蒺藜苜蓿对低P胁迫的适应策略不同,低P胁迫下,黄花苜蓿主要通过根系大量分泌柠檬酸,活化根际难溶态P来提高对P的吸收,而蒺藜苜蓿维持较大的根系是其适应低P胁迫的主要策略。
Low levels of soil available phosphorus (P) are one of the major constraints on plant growth. Root morphology and root excretion of large amounts of citric acid-based organic acids is an important mechanism to adapt plants to P deficiency in soil. Using sand culture method, Medicago falcata (Medicago falcata) and Medicago truncatula (Medicago falcata), which are widely distributed in northern China, were used to study the effect of low P stress on plant growth, root morphology and Citric acid secretion, compared two different alfalfa adapt to low-P stress different strategies. The results showed that: 1) Low P treatment significantly inhibited shoot growth of Medicago truncatula and Medicago truncatula, while had little effect on the growth of the ground, resulting in an increase in root / shoot ratio. 2) Low P stress significantly reduced the total root length and lateral root length of Medicago truncatula, but had no significant effect on the above root morphology index of Medicago truncatula. 3) Low-P stress promoted citric acid secretion in roots of both alfalfa cultivars, and the amount of citric acid secreted by root of alfalfa was significantly higher than that of Medicago truncatula at either normal or low P stress. The above results showed that Medicago truncatula and Medicago truncatula had different adaptation strategies to low P stress. Under low P stress, Medicago falcata increased the absorption of P mainly by excreting citric acid abundantly in the root system and activating hardly soluble P in the rhizosphere. However, Medicago truncatula Maintaining a larger root system is its main strategy to adapt to low P stress.