干旱区水力提升的生态作用

水力提升是某些植物通过深层根系从较湿的深层土壤中吸取水分再通过浅层根系在较干的浅层土壤中释出的过程。水力提升所释出水量及其释出过程具有积极的生态学意义，它不但为伴生植物提供新的水源、改善其邻近植物的蒸腾作用、缓解水分亏缺、提高水分利用效率．而且促进植物的养分吸收、促进上层干土中分解、硝化和矿化等生化过程．尤其是发生在克隆植物植株间的水分共享这种特殊的水力提升，还影响群落的形成。然而，对于一般的水力提升而言，水力提升所释出水量到底有多少。其生态学作用有多大．有待深入研究。结合研究实践认为．要研究水力提升具有多大的生态学作用．必须准确地区分水；勺提升的水量和毛管水的上升水量。还建议了研究水力提升新的研究方法。

Discussion on ecological role of hydraulic lift in arid region

An effort has been made to review the ecological role of hydraulic lift and discuss the existing questions in the research field. Hydraulic lift is the process by which some deep-rooted plants take in water from deeper soil layers and exclude that into shallower, drier soil layers. According to the published papers, hydraulic lift is of important ecological significance. Hydraulically lifted water (HLW) can benefit the plant that lifts it as well as benefit neighboring plants. Hydraulic lift not only provides new water resource, improves transpiration and postpones water deficit, increases water use efficiency for accompanying plants, but also promotes nutrient absorption of hydraulic lifter and accelerates the process of biochemical cycle, such as catabolism, nitration and mineralization. Especially, water sharing that takes place in inter-ramet of colonal plant, acting as a kind of special hydraulic lift, influences the formation of communities. The volume of HLW can be such that it might influence seasonal water balances of individuals, communities, or even ecosystems. If this phenomenon is widespread, it should be incorporated into models of competitive interactions, as well as ecosystem process models and water budgets. Hydraulic lift, therefore, is a potentially important ecosystem process. Although there are many evidences of discovering hydraulic lift, how many the volume of HLW is there? Although hydraulic lift is actually existent as a physiological phenomenon for some plants, how to value its ecological role correctly? The key to discuss these questions is to distinguish HLW and capillary water in soil accurately, which is an essential condition to study hydraulic lift and is also a basis on estimating its ecological role. In the arid region (including semi-arid region), strong evaporation makes capillary action in soil intensive in day. When air temperature drops quickly and soil temperature drops slowly at night, capillary water accumulates in shallower soil layers and makes water content in soil high there. In an experiment of ours, a phenomenon was observed, i.e., water content in the soil of 20cm deep increased obviously running 10 whole days at night after Calligonum caput-medusae Schrenk was irrigated 5 whole days with basin irrigation in an irrigation period in the hinterland of Taklimakan Dessert. This illustrates the plant may be a hydraulic lifter, but the increased water content contained some capillary water surely. Therefore, choosing adequate method to research hydraulic lift is necessary. After three kinds of methods to study hydraulic lift were reviewed, we found most of them cannot distinguish HLW and capillary water in soil accurately. In order to determine HLW accurately and estimate the ecological role of hydraulic lift correctly, a new method was put forward in the paper. The purpose is promoting the research of hydraulic lift in the future.