摘要
对根 -土界面水分再分配的研究背景 (概念、发现及证据 )、普遍性与再分配的水量及其生理生态学意义 (对相邻植物利用水分、根际活动、土壤 -植物 -大气系统水分传输和根系可塑性发育的促进效应 )等进行了深入论述 ,对水分再分配的认识和研究方法进行了探讨 。
Based on our own research work, the following aspects of hydraulic redistribution(HR) between the interface of roots and soil are discussed. HR usually occurs at night when transpiration has diminished sufficiently to allow the roots' water potential to exceed the drier soil water potential(Ψ_s)in the soil profile. Although the direction of water movement in the process of root HR is typically upward, towards drier, more shallow soil layers, recent measurements of sap flow in taproots and lateral roots of trees have demonstrated that roots can also redistribute water either downward or laterally from moist surface soils to drier regions of soil. “Hydraulic redistribution” has been proposed as a more comprehensive term than “hydraulic lift” to describe this phenomenon in considering that it can be bi-directional and is apparently passive. Water released from roots into drier soil layers may be reabsorbed when transpiration exceeds water up-take by deep roots only. Redistribution of soil water through root systems has been demonstrated in greenhouses, laboratories and field experiments. The first strong evidence for HL occurring in the field was observation of diurnal fluctuations in Ψ_s that gradually increased at night and sharply declined during the day, associated with the shrub Artemisia tridentata. Our own observations of HL in the half-shrub Gutierrezia sarothrae with a shallow roots system indicates that the HL improved water uptake during the day when evaporation is high and less water is available in the topsoil. So far HR has been reported in forty -three woody and sixteen herbaceous species distributed over different climatic regions, which indicates that the phenomenon of HR is not restricted to only arid and semiarid environments. The quantities of water redistributed by roots were affected by many factors, such as daily evapotranspiration(ET)and root length densities. A considerable amount of water is lifted by roots each night. Estimates of hydraulically lifted water range from 14% of daily ET for the suffrutescent shrub G. sarothrae to roughly one-third of daily ET for the shrub A. tridentata. From 3% to 60% of the redistributed water can be utilized by neighboring plants, as many of these species are in close proximity to one another. In addition, the reoccurrence of HR over significant periods of time in dry upper soil layers has several implications for rhizosphere processes and plant nutrient acquisition. These include prolonging the activity and life span of fine roots, improving nutrient ion mobility, and potentially smoothing spatial heterogeneity of nutrients. HR can facilitate water movement in the soil-plant-atmosphere system by improving ET for plants. The root plasticitally adapting itself towards very dry soil or sand below its depth might be facilitated by the water transfer from the moist surface soil to dry deep soil following a precipitation event. The process of water moving from upper to lower drier soil layers along an inverted water potential gradient in the soil profile was termed “inverse hydraulic lift”. Although much progress in research on HR has been made, there are still some contradicting points of views about HR. There are a few reports on alfalfa and cotton which show that roots of some species largely prevent reverse water flow. Some studies have concluded that the quantities of water redistributed by this process are minute. Three methods to measure HR were tested, but measuring the changes of soil water content and soil water potential(Ψ_s)around plant rhizosphere proved to be the most convenient. In addition, the reduction in transpiration can serve as an indirect measurement of the quantity of hydraulically lifted water. Though several challenging studies on HR have been conducted, further investigation into the effects of HL on the water balance of neighboring plants and the influence of HR on water movement in the soil-plant-atmosphere system needs to be done. We propose further studies on HR based on the above discussion: the magnitude of H
出处
《生态学报》
CAS
CSCD
北大核心
2004年第5期1040-1047,共8页
Acta Ecologica Sinica
基金
国家自然科学基金资助项目 ( 90 10 2 0 11
3 0 3 710 2 3
3 973 0 10 0 )~~
关键词
根—土界面
水分再分配
水分提升
生理生态学意义
现状
展望
interface of root and soil
hydraulic redistribution
hydraulic lift
significance of physiological ecology
present situation
prospect
