越冬紫花苜蓿根系性状与秋眠性的关系及其抗寒效应

Response of Alfalfa Root Traits to Fall Dormancy and Its Effect on Winter Hardiness

【目的】秋眠是紫花苜蓿(Medicago sativa)对晚秋生长环境变化的一种适应性反应,根系是紫花苜蓿越冬的主要功能器官,秋眠性与其越冬具重要关联,但对于如何通过根系性状的越冬特征来实现抗寒效应,仍不清楚。文章中从根系性状越冬反应的角度,探究秋眠性对紫花苜蓿抗寒性的作用过程。【方法】采用11个标准秋眠级紫花苜蓿品种为材料,以紫花苜蓿在中国适宜分布区中较为寒冷的中温带地区为例,通过标准主轴分析(standardized major axis,SMA)等方法,研究不同秋眠级紫花苜蓿各根系性状在越冬过程的差异化响应及其异速生长关系,进一步采用偏最小二乘回归(partial least squares regression,PLSR)等方法,研究不同秋眠型紫花苜蓿通过根系策略来实现其抗寒效应的关键作用因子。【结果】(1)随着秋眠性的减弱(即秋眠级提高),越冬紫花苜蓿根颈直径和侧根数显著减小(P<0.05),秋眠性较强的紫花苜蓿具有增强储藏的表型特征,而主根直径、侧根直径等则随着秋眠性的减弱而显著趋于增大(P<0.05),侧根数量与侧根的其他特性表现一定的权衡关系(P<0.05);(2)受秋眠级的影响,根系性状之间表现显著的异速生长关系,主要表现在根颈入土深度、侧根位置、侧根数等性状之间,其异速生长斜率与1存在显著差异(P<0.05),不同根系性状在越冬期间对秋眠级具有不同的响应策略;(3)紫花苜蓿越冬率与秋眠级具有显著的负相关关系,但并非线性响应,而是呈现逻辑斯蒂曲线变化特征,1—5秋眠级趋于稳定在高越冬率水平(>95%),中间级别5—8级的越冬率逐渐急剧减小(50%—70%),9—11级在中高纬度难以越冬(<5%);(4)影响紫花苜蓿越冬率的正向贡献因子是根颈直径、侧根数(P<0.05),而主根直径、侧根直径等因子的提高反而降低了紫花苜蓿的抗寒性(P<0.05),根系直径等性状并非决定抗寒能力的主导因子。【结论】不同秋眠级紫花苜蓿的根系性状表现出对越冬低温胁迫的差异化响应特征,不同性状具有异速生长关系;紫花苜蓿主要通过增加根颈直径和侧根数来提高其抗寒性,并不取决于根系其他表型性状的绝对大小;越冬期间,不同秋眠型紫花苜蓿根系策略的适应性变化,是实现其抗寒效应的重要途径。

Objective]Fall dormancy of alfalfa （Medicago sativaL.） is an adaptive strategy in response to change of temperature and lighting in the growth environment in late autumn. Roots, as the main functional organ of alfalfa, play a vital role in surviving the winter. Although previous studies have shown that there are significant correlations between fall dormancy and cold resistance, the overwintering characteristics of alfalfa roots on cold resistance are not clearly understood. The aim of this study was to determine the role of fall dormancy on winter hardiness in consideration of aspects of root traits.[Method] Eleven alfalfa standard check cultivars were chosen and grown in semi-arid temperate regions, which is an appropriate area for alfalfa cultivation in China. Using the standardized major axis （SMA） method, the allometric scaling of different root traits in response to fall dormancy in the process of overwintering was studied. Furthermore, using partial least square regression （PLSR） and other methods, the master regulators of the effects of alfalfa with different fall dormancy types on cold resistance in root phenotypic traits were analyzed.[Result]The results showed that with increasing fall dormancy rating, from one to 11, the collar diameter and lateral root number of wintering alfalfa significantly decreased （P〈0.05）. More dormant alfalfa was accompanied with enhanced storage phenotypic characteristics. However, taproot diameter and lateral root diameter significantly increased （P〈0.05） as alfalfa became more non-dormant. Tradeoffs were found between lateral root number and other lateral root traits （P〈0.05）. Affected by fall dormancy ratings, root traits performed notable allometric scaling of different parts, mainly in collar depth, lateral root position, and lateral root number. Significant differences （P〈0.05） existed between allometric scopes and one （P〈0.05）. Therefore, different root traits had differentiation strategies during the overwintering process. There were significantly negative correlations between the alfalfa winter survival rate and fall dormancy rating. The negative correlation could be fitted by logistic curve but not by a linear equation. Alfalfa cultivars with a fall dormancy （FD） rating of 1-5 tended to have a higher winter survival rate （〉95%）, 6-8 FD tended to have a sharply decreased winter survival rate （50%-70%）, and 9-11 rarely survived in winter （〈5%）. Collar diameter and lateral root number were positive contribution factors in the alfalfa winter survival rate （P〈0.05）, but the taproot diameter and lateral root diameter, negative contribution factors, were not main factors that decided the winter hardiness in alfalfa （P〈0.05）.[Conclusion]Root traits of alfalfa with different fall dormancy ratings performed differentiation strategies in response to low-temperature stress in winter, followed by allometric relationships among different traits. Alfalfa enhanced its winter survival rate mainly through increasing collar diameter and lateral root number, and did not depend on the absolute size of other root phenotypic traits. Overall, during wintering, adaptive changes of root traits of alfalfa with different fall dormancy ratings are a primary pathway to improve winter survival.