Abstract: Soil-plant-atmosphere continuum (SPAC) is the core in studying plant water use and water cycle. To study the water transportation process of SPAC is of significance for the vegetation restoration in arid regions. From the aspects of soil moisture and plant transpiration, this paper summarized the study methods of soil moisture, mainly thermal inertia method, neutron probe method, and time domain reflectometry, and the study methods of plant transpiration at foliage scale, single wood scale, stand scale, and regional scale. The applications of stable isotope method in the study of plant water sources were also highlighted.

Key words: alpine treeline, Larix potaninii, litter decomposition, organic fraction.