关键词: 异形叶, Corner法则, 异速生长, 枝叶大小关系, 水力运输, 资源分配策略

Abstract:

Objective: The purpose of this study is to analyze whether changes in the twig-leaf size relationships could reduce the drought stress of Populus euphratica with heteromorphic leaves, which could provide reference for clarifying the formation mechanism of heteromorphic leaves and the conservation of P. euphratica individuals. Method: Three main heteromorphic leaves, i.e., ovate, nearly ovate and lanceolate leaf, of P. euphratica in the Ebinur Lake Wetland National Nature Reserve in the Xinjiang, China, were taken as the research object. The cross-sectional area of twigs, the total leaf area on the twigs, the hydraulic and anatomical traits were determined experimentally in 18 P. euphratica individuals, and then the standardized major axis regression (SMA) was used to compare the difference in the relationship of size between twig and leaf among three heteromorphic leaves. Multi-correlation analysis was conducted to test the effects of the twig-leaf size relationships on the hydraulic and anatomical traits. Result: 1) There was a significant isometric growth relationship between the cross-sectional area of twigs and the total leaf area. The regression slope of twig-leaf size relationships ranged from 0.65 to 1.06; which had no significant difference compared with 1 (P> 0.05). 2) The SMA results showed that there was a common slope (a = 0.83) for the regression of the total leaf area to twig cross-sectional area among heteromorphic leaves. Under the condition of common slope, the intercept (b) differed among the three heteromorphic leaves: ovate (1.41) > nearly ovate (1.35) > lanceolate leaf (1.25). 3) There were significant differences in leaf length, leaf width, leaf length-width ratio, maximum transpiration rate, Huber value, stomatal size and density, and palisade tissue thickness among the three heteromorphic leaves (P < 0.05), while pre-dawn leaf water potential and specific conductivity of twigs were not different (P> 0.05). 4) The twig-leaf size relationship was significantly correlated with Huber value, stomatal size and density, palisade tissue thickness, maximum transpiration rate and pre-dawn leaf water potential (P < 0.05). Conclusion: The isometric growth relationship between twig and leaf is an adaptive strategy of P. euphratica to maintain the balance between water transport and mechanical support. Under the condition of the same cross-sectional area of twigs, the total area of ovate leaf was higher than that of nearly ovate, and even higher than that of lanceolate leaf. The change of the twig-leaf size relationship of P. euphratica could improve the hydraulic properties, thereby increase the water transport capacity and reduce the drought stress.

Key words: heteromorphic leaves, Corner rule, allometric growth, twig-leaf size relationship, hydraulic transportation, resource allocation strategy