Indication of Stable Isotope Composition on the Process of Oasification and Desertification in Arid Regions: A Case Study in the Heihe River Basin

Abstract:

Oasification and desertification are the two main land surface processes contrarily correlated with each other in arid regions. It is useful for environmental indication research to clarify the relationship between plants and environment under the oasification and desertification processes in arid regions. In the Heihe River basin, the most representative areas of oasification and desertification in China, we carried out a study to test whether or not we can use plant and soil stable isotope signature as an indicator of changes in key land surface process. Stable carbon (δ¹³C) of plant leaves, hydrogen (δD) and oxygen (δ¹⁸O) isotopes of plant stem water and potential water sources were analyzed to investigate the water use efficiency (WUE) and water sources of different plant species in three typical habitats (oasis, oasis-desert transitional zone, desert). The results suggest that plants in the desert habitat tended to use water from deeper soil layer (>160 cm). In the oasis-desert transitional zone, Artimisia arenaria and Calligonum mongolicum were likely used water mainly from the soil layer about 20-40 cm in depth, Haloxylon ammodendron utilized water primarily from 60-80 cm in depth, Hedysarum scoparium may use water from soil layer about 100 cm in depth and Tamarix ramosissima obtained its water from deeper soil layer(>120 cm). Plants in the oasis habitat used soil water mainly from 0 to 100 cm soil layers. Calamagrostis pseudophragmites used water about 20 cm in depth, Zea mays extracted soil water from the depth of 20-40 cm, and Tamarix ramosissima and Populus simonii obtained soil water about 60 cm in depth. The δ¹³C values of C₃ plants in each habitat differed significantly. In the oasis zone, WUE of shrubs were more positive than this of grass, which were similar to the conclusions of the previous studies. Among the three habitats, plants in oasis-desert transitional zone had the most positive δ¹³C values whereas plants in oasis area had the most negative values. This pattern may have resulted from soil texture, soil water content and plant water sources differences among the habitats. Overall, the results of our study illustrated that plant and soil isotope composition are useful for the indication of the processes of oasification and desertification in arid regions.