摘要:以直立型扁蓿豆[Medicago ruthenica(L.)Sojak.cv.Zhilixing]为材料，于苗期连续干旱处理12 d后复水4 d，研究直立型扁蓿豆幼苗形态结构特征、生理代谢及生物量分配对干旱胁迫及复水的响应，揭示直立型扁蓿豆对干旱胁迫及复水的适应策略。结果表明：随着干旱胁迫时间延长，直立型扁蓿豆叶片气孔开放率逐渐降低，处理9 d后气孔及表皮细胞密度比正常浇水处理(CK)分别增加48.5%和36.6%，形成小而密的表皮细胞和气孔。生理上，除MDA含量随胁迫时间的延长逐渐增加外，其余指标均先升高后降低，干旱胁迫9 d时达最高，SOD、POD、叶绿素、可溶性糖、可溶性蛋白及脯氨酸分别较CK提高88.9%、111.2%、86.7%、140.5%、147.8%和124.6%。同时，生物量随胁迫时间的延长先增大后减小，于干旱胁迫9 d达最大值，比CK增加16.4%，总的分配格局表现出地上生物量投资高于地下，地下生物量投资比例随胁迫时间的延长逐渐增加，而地上生物量变化与其相反。复水后各指标均能恢复至CK水平或超过CK，表现出极强的复水敏感性和潜在恢复能力。该品种扁蓿豆对干旱胁迫及复水的适应主要分为3个时期：主动适应期，其生理参数的可塑性指数为形态参数的1.33倍，主要通过抗氧化及渗透调节来减少水分散失增加水分吸收、缓解氧化伤害以适应干旱逆境；被动适应期，其形态参数的可塑性指数为生理参数的1.31倍，主要采用牺牲生物量的生存策略以及降低色素含量减少光吸收的光保护机制来提高逆境下的生存能力；复水恢复期，根冠比、气孔开放率、气孔及表皮细胞密度比CK分别增加25.9%、29.7%、24.2%和16.3%，其较高的根冠比和叶片较高的气孔开放率及小而密的气孔及表皮细胞特征，保证了直立型扁蓿豆吸水能力以及水分运输效率的迅速恢复。综上，直立型扁蓿豆抗旱能力较强，能够通过形态生理的改变以及调整不同器官的生物量分配来应对与适应干旱逆境及复水，且在不同处理阶段采取不同的适应策略以达到生存目的。
关键词:直立型扁蓿豆/
干旱胁迫/
复水/
形态/
生理/
适应策略/
叶片表皮细胞/
气孔密度
Abstract:The effect of drought stress and rehydration on Medicago ruthenica (L.) Sojak cv. Zhilixing morphological structures, physiological metabolism, and matter distribution were investigated to determine the adaptation strategy in an arid environment. Seedling-stage M. ruthenica (with 6-8 leaves) were subjected to continuous drought stress for 12 days and then re-watered for 4 days; samples were collected from the control group (CK), after 9 and 12 days of drought stress, and 4 days after rehydration. Compared with the CK, the stoma opening rate decreased, while the stoma and epidermis cell densities increased by 48.5% and 36.6%, respectively. Smaller and denser epidermal cells formed. The malondialdehyde (MDA) content increased gradually during stress period. Superoxide dismutase activity (SOD), peroxidase activity (POD), and contents of chlorophyll, soluble sugar, soluble protein, and proline first increased and then decreased with prolonged drought. Total biomass also first increased then decreased, reaching the maximum after 9 days (0.433 7 g; 16.4% increase). The distribution of the above-ground biomass was higher than the under-ground biomass, and the under-ground biomass proportion increased with drought, while the opposite effect was observed with the above-ground biomass. After re-watering, all of the physiological and biochemical indexes recovered or exceeded those of the control, indicating strong rehydration sensitivity and resilience. M. ruthenica adaptation to drought stress and rehydration was divided into three periods:active adaptation, passive adaptation, and re-watering. The physiological parameter plasticity index was 0.16, 1.33 times greater than the morphological parameter index, during the active adaptation period. Drought stress adaptation was achieved by altering the antioxidant and osmotic regulation systems to reduce water loss, improving water retention and absorption efficiency, and maintaining the water absorption and loss balance. The morphological parameter plasticity index was 0.24, 1.31 times greater than the physiological parameter index, during the passive adaptation period. M. ruthenica sacrificed biomass and reduced pigments to aid survival. The root-shoot ratio (25.9%), stomatal opening rate (29.7%), and stomatal and epidermal cell density (24.2% and 16.3%, respectively) were higher than those in the CK during the re-watering period. These characteristics promoted rapid water recovery, absorption capacity, and water transport efficiency. Morphological and physiological changes allowed M. ruthenica to adapt to drought stress and rehydration, contributing to its survival in arid conditions.
Key words:Medicago ruthenica (L.) Sojak. cv. Zhilixing/
Drought stress/
Rehydration/
Morphology/
Physiology/
Adaptive strategy/
Epidermis cell of leaf/
Stomatal density
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