Variation of soil-plant-atmosphere continuum stable isotope and water source in Qinghai spruce forest of the eastern Qilian Mountains

Understanding the hydrogen and oxygen stable isotope composition and characteristics of different water bodies in soil-plant-atmosphere continuum is of significance for revealing regional hydrological processes and water cycle mechanisms.In this study,we analyzed the stable isotopic composition,relationship and indicative significance of precipitation,soil water(0~100 cm depth)and xylem water of Qinghai spruce(Picea crassifolia)forest in the eastern Qilian Mountains,and explored the circulation process among different water bodies.The results show that the stable isotopes of precipitation vary greatly during the entire observation period.The values ofδ2H andδ^(18)O in the precipitation in the warm season are richer than those in the cold season,and the slope and intercept of local meteoric water line(LMWL,δ2H=6.79δ18O+7.13)are both smaller than global meteoric water line(GMWL,δ2H=8.17δ18O+10.56).The stable isotopes of soil water at different depths underwent different degrees of evaporative fractionation,and theδ18O andδ2H of shallow soil water varied greatly,while the deep soil water tended to be similar.The topsoil(0~10 cm)can respond quickly to precipitation,and the response of the deep soil has a time lag.In the whole growing season,0~30 cm and 60~100 cm soil water are the main water sources of Qinghai spruce.The water source of Qinghai spruce was from all soil layers in May and September,mainly from the shallow soil layer(0~30 cm)in August and October,and mainly from the deep soil layer(60~100 cm)in June and July.

Water utilization of typical plant communities in desert steppe,China

Water is a limiting factor in the restoration and construction of desert steppe.Exploring plant water sources is necessary to understand soil-plant interactions and species coexistence;however,water sources of major plant communities within the desert steppe of Ningxia Hui Autonomous Region,China remain poorly understood.In this study,we analyzed the water uptake of plants in four typical communities:Agropyron mongolicum Keng.;Sophora alopecuroids Linn.;Stipa breviflora Griseb.,and Achnatherum splendens(Trin.)Nevski communities.Stable isotopesδD andδ^(18)O in the xylem of plant and soil water at different soil depths were analyzed.An IsoSource model was used to determine the soil depths from which plants obtained water.Results showed that A.mongolicum community obtained water predominantly from 0–20 and 40–80 cm depth,S.alopecuroids community from 0–20 cm depth,S.breviflora community from 0–40 cm depth,and A.splendens community from 0–20 and 80–140 cm depths.S.alopecuroides had a wider range of soil depths for water extraction,i.e.,utilizing different water sources depending on habitat,and the plasticity of its water uptake pattern determined its role in different communities.Water source of plants relayed heavily on the distribution of their roots.Competition for soil water exists between different plant life forms in the sierozem habitat(A.mongolicum,S.alopecuroids,and S.breviflora communities),and in the sandy soil habitat(A.splendens community).The use of soil water by A.splendens community is more spatially differentiated,and shrubs and herbs can coexist stably.Under the pattern of extended drought period in the future,sierozem habitat may be more favorable for the formation of a dominant monoculture community type of perennial fibrous plants.In aeolian sandy soil habitat,A.splendens had a strong competitive advantage,and the growth of shallow-rooted plants was easily suppressed.