植物抗旱性中的补偿效应及其在农业节水中的应用

在论述植物补偿效应存在类型和研究范畴的基础上,详细评述了植物抗旱性中根系形态结构功能及地上部干物质积累、产量和水分利用效率方面的补偿效应及其影响因素,并对植物抗旱作用中补偿生长的可能生理学机制作了探讨。同时,对补偿效应在提高农业水分利用效率中的应用进行了讨论

The compensatory effect in drought resistance of plants and its application in water-saving agriculture

In biology, compensation is a common phenomenon following environmental stresses such as drought, anoxia, salinity, and nutrient stresses. In some cases, stress is steady or unchanging. This may result in some adaptive responses by the plant. But in other cases, the plant may be exposed to fluctuating stress conditions. The compensatory effect may develop when there is an uneven supply of resources or when the plant's environment fluctuates between stressful and nonstressful conditions. We propose that the compensatory effect develops when plants are grown under conditions of fluctuating stress. As a result of the compensatory effect, plant morphology or function may equal or even surpass that of plants grown under nonstressed conditions. In contrast, plants grown under steady stress conditions exhibit other kinds of adaptive responses. These responses often offset each other. For example, under steady stress conditions, enzyme concentrations in a plant may go down, but the enzyme activity may go up. This should not be considered to be a compensatory effect. In this paper, we also distinguish among different types of compensatory effects based on the level and effect of compensation, as well as the number and fluctuation pattern of the environmental stresses. This review describes the compensatory effect on plant attributes such as biomass accumulation, water use efficiency, and the morphology and function of root systems. Compared to treatments that have sufficient and steady soil water contents, crop production and water use efficiency increase significantly when plants are exposed to drying and rewetting cycles. Roots tend to grow and proliferate in regions of high water availability. The hydraulic conductivity of roots increases noticeably under a locally restricted water supply. This also occurs after drying and rewetting cycles. The compensatory effect in these plants can be attributed to five physiological processes: (a) the maintenance of root growth during periods of mild water deficit; (b) the improvement of the morphology and function of the root system after the drying-wetting cycle; (c) the improvement of osmotic adjustment in the extension zone of both roots and leaves during the drying-wetting cycles; (d) the rapid recovery of photosynthesis during rewetting after a period of mild water deficit; and (e) changes in the allocation and reserve of assimilates during periods of water deficit. The plant hormone abscisic acid (ABA) plays an important role in the first three processes by regulating hydraulic conductivity, the extensibility of the cell wall, and osmotic adjustment for the maintenance of turgor pressure. The factors influencing the compensatory effect in the drought resistance of plants include the species, variety, plant development stage, and the intensity and duration of the water deficit. This paper also provides some examples for the application of the compensatory effect in water-saving agriculture. In the case of regulated deficit irrigation, a mild water deficit is maintained during the early stages of plant growth. This irrigation pattern induces the compensatory effect and results in an improvement in crop quality and/or yield. Controlled alternate partial root-zone irrigation is an alternative water-saving method that takes advantage of the compensatory effect and increases water absorption from localized areas. Unique irrigation regimes are required for different crop species in order to realize optimum compensatory effects.