| Plant form can significantly affect its water transportation and gas exchange traits,but it is still obscure whether there is a difference of the leaves and shoots between the upgrowing and sagging shoots.In the upward growth of shoots,water transportation needs to overcome reverse transportation resistance which is the main factor limiting the plant water transportation and the maximum plant height,while the direction of gravity will promote the transportation of water in the sagging shoots.Therefore,we hypothesis that there are differences between the hydraulic characteristics and the gas exchange characteristics of the shoots with different orientation,thus adapting to the micro-environment.Two willows with different shoot forms are selected as the experimental materials in this study(Salix babylonica with sagging shoot form and Salix matsudana with upgrowing shoot form).We measured leaf water potential,max leaf hydraulic conductance,leaf vulnerability curve,shoot vulnerability curve,PV curve(pressure volume curve),the anatomical structure of leaf and shoot,leaf to the sapwood area,the photosynthesis curve,the stomatal vulnerability curve,etc.The follows are results obtained:1.Compared with upgrowing willow,the sagging willow has longer shoot,larger single leaf area,higher leaf to the sapwood area ratio,weak water anti-gravity transportation capacity,higher shoot and leaf water transport efficiency,but the shoot and leaf water safety is lower than the upgrowing willow.The trade-offs between hydraulic efficiency and safety is exist in leaves and shoots of two species.2.The vessel diameter of the leaves and shoots of the sagging willow is wider than upgrowing willow and the vessel length of sagging shoot is longer too.The vessel density and vein density of upgrowing willow are less than that of the upgrowing willow.3.The stomatal conductance,photosynthesis rate and transpiration rate of upgrowing willow leaf respond to the intensification of water stress in a slow manner,showing the stomata is not sensitive to drought stress.The leave of it cannot maintain stable water supply and keep high water use efficiency before stomatal closure.4.The stomatal conductance,photosynthesis rate and transpiration rate of the sagging willow decrease rapidly with the increase of water stress,showing the stomatal is sensitive to drought stress.Before the closure of stomatal,the leaves of the upgrowing willow can maintain high and stable ratio of water supply and demand and higher water use efficiency.This study reveals that the leaves and shoots with different shoots forms with different hydraulic and gas exchange adaptation characteristics,there is a trade-off between the hydraulic efficiency and safety of the leaves and shoots in two species,the sagging willow leaves adopt a conservative water use strategy,while the upgrowing willow leaves adopt risky water use strategy.These differences reflect the difference between species with different shoot forms to some extent.This study enriches our understanding of the hydraulic systems affected by plant morphology and deepens our understanding of the different hydraulic systems obtained by same genus that are distributed in similar habitats and their potential impact on plant micro-habitats. |
