土壤-根系统水分再分配:土壤-植物-大气连续体中的一个小通路

doi:10.17521/cjpe.2007.0101

摘要/Abstract

摘要：

吸收和传导水分一直被视为植物根系最主要的功能之一,而人们对根系在某些情况下还可以向土壤释放水分的事实及其对植物生长和生态系统功能的影响了解得还很不充分,尽管这样的证据由来已久。土壤-根系统水分再分配(Hydraulic redistribution, HR)是近20年间被发现和证实的,指水分从土壤中较湿的部分经由植物的根系传导而运动到土壤中较干的部分,通常发生在蒸腾减弱的夜间,可以沿水势梯度下降的方向而在不同土层间向上向下或侧向运动。HR研究揭示了土壤-植物-大气连续体中有时会存在土壤-根-土壤的水流小通路,细化了土壤-根系统中水分储存和运输的时空动态和机制。土壤水分状况的连续监测、根木质部液流测量、稳定性同位素技术的使用构成了HR实验研究的三大手段。当土壤中深层水分充足的时候,HR可以提高根系吸收和传导水分的效率,有利于植物充分利用资源,延长了浅层土壤的水分可利用期,有利于维持植物组织的生理活性和水流传导;旱季后降水来临的时候,HR可以将一部分降水转移到深层土壤,增加了可利用性水分的总量。对于干旱半干旱的沙地和草原、季节性干旱的森林等类型,HR过程可能对生态系统水分循环产生重要影响。有必要在国内针对这些生态系统展开深入的实验研究,同时探索将HR过程适当结合到生态系统模型和水文模型中,从而更准确地研究和预测群落内植物水分关系和生态系统水分动态。此外,结合农林设计、植被恢复、生态需水量估算和农业节水等方面进行的HR研究也值得深入探索。

关键词: 水分提升, 水分下传, 土壤水势, 土壤水分含量, 木质部液流, 水流导度, 植物生理生态, 生态水文

Abstract:

Water uptake is generally accepted as the most important function of plant roots, while the fact that roots can also release water to soil and its ecological consequences and significance to ecosystem function are not well understood. Studies in the past 20 years confirmed the existence of hydraulic redistribution (HR), which describes the passive movement of water from moist soil to dry soil via roots when transpiration ceases (usually at night). The direction of HR can be upward, downward or lateral in soil along water potential gradients. Because this newly recognized small cycle of soil-root-soil exists within the Soil-Plant-Atmosphere Continuum (SPAC), the mechanism of dynamic movement and storage in the soil-root system has interested many functional ecologists. Continuous measurement of soil water potentials or contents and root sap flow and the use of stable isotopes techniques have been extensively used in HR research. HR acts as a good feedback mechanism between plant water status and soil water dynamics. When deep soil water is plentiful, HR could enhance the efficiency of water uptake via roots, helping plants to make full use of water to improve transpiration and photosynthesis rates and hence maintain physiological function and hydraulic conductivity of the SPAC system. When rainfall comes after the dry season, more precipitation could be transferred to deep soil as an effective storage because of HR, thus increasing availability of rainfall to plant growth. HR was significant for water flux in some ecosystems, for example arid-semiarid sandlands and grasslands, as well as seasonal dry forests. Experiments on HR in Chinese ecosystems are expected or are already underway. On the other hand, integrating HR into ecosystem and hydrology models to study the water relationships between neighboring plants and predict the dynamics of ecosystems with HR is also important. The implications of HR to designing agro-forestry, vegetation recovery, calculating ecological water demand and water conservation in agriculture also deserve more attention.

Key words: hydraulic lift, hydraulic descent, soil water potential, soil water content, sap flow, hydraulic conductance, plant physiological ecology, ecohydrology

刘峻杉, 高琼, 朱玉洁, 王昆. 土壤-根系统水分再分配:土壤-植物-大气连续体中的一个小通路. 植物生态学报, 2007, 31(5): 794-803. DOI: 10.17521/cjpe.2007.0101

LIU Jun-Shan, GAO Qiong, ZHU Yu-Jie, WANG Kun. HYDRAULIC REDISTRIBUTION: NEWLY RECOGNIZED SMALL CYCLE WITHIN THE SOIL-PLANT-ATMOSPHERE CONTINUUM. Chinese Journal of Plant Ecology, 2007, 31(5): 794-803. DOI: 10.17521/cjpe.2007.0101

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链接本文: https://www.plant-ecology.com/CN/10.17521/cjpe.2007.0101

https://www.plant-ecology.com/CN/Y2007/V31/I5/794

图/表 2

图1 电路示意图表示的简单二层土壤-植物系统阻力分布 r1:气孔阻力 Stomatal resistance r2:茎和叶脉木质部阻力 Xylem resistance aboveground r3、r4:根木质部阻力 Xylem resistance in the roots r5:浅根的径向阻力 Radial resistance in shallow roots r6:深根的径向阻力 Radial resistance in deep roots r7:土层之间的水流阻力 Resistance between different layers of soil A、B、C分别代表叶片表面、浅层土壤和深层土壤处的水势 A、B、C as water potential of the leaf surface, shallow soil and deep soil respectively

Fig.1 The resistances in the soil-plant system illuminated as electricity circle

图2 3种典型的HR格局 a. 夜间发生HL,而白天深浅根都为正向流 HL occurred in night, while daytime HL disappeared b. 昼夜持续的HL HL occurred day and night c. 发生HD HD occurred usually after rainfalls (Lee et al. 2005) HR: 水分再分配 Hydraulic redistribution HL: 水分提升 Hydraulic lift HD: 水分下传 Hydraulic descent

Fig.2 Three typical HR patterns

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