Variation in water use patterns of three typical plants in a dune-meadow cascade ecosystem of the Horqin Sandy Land: Implications from stable isotope compositions

In the Horqin Sandy Land, the dynamics of the soil-plant-atmosphere-water system and changes in plant water availability significantly impact water resources management and vegetation restoration. This study determined the hydrogen and oxygen isotopic compositions (δD and δ18O) of precipitation, plant water, soil water, and groundwater as well as carbon isotopes of plant leaves during the growing season and different precipitation events (8.9 mm, 18.1 mm, and 28.3 mm) in 2020. Target areas included a semimobile dune with Artemisia halodendron communities (SMAH), a meadow corn field (MCF), and a meadow wetland dominated by Phragmites australis (MPA). The water uptake patterns of the three typical plants were determined using the Iso-Source model. The results showed significant differences in the seasonal variations of δD and δ18O in precipitation, plant water, soil water, and groundwater among SMAH, MCF, and MPA throughout the water cycle, which was attributed to the different origins, distribution, and evaporation mechanisms of water. The influence of precipitation on soil water transport processes varied with the change and transformation of rainfall intensity and ecosystem type. Water conditions and root distribution determined seasonal water use patterns of three plants. The water use efficiency (WUE) of the three typical plants followed the order: corn > Phragmites australis > Artemisia halodendron. And their seasonal WUE were not only consistent with the contribution rate of deep soil water, but also affected by the water use strategies adopted. However, the response of their WUE to rainfall pulses was not significant on the whole. Rainfall intensity, pre-rain mass soil moisture content characteristics and vegetation characteristics are important factors affecting the contribution distribution of different water sources to plants under rainfall events. Artemisia halodendron displays ecological plasticity against seasonal water deficit, facilitating its extensive colonization in dune ecosystem and further promoting the process of dune fixation. The distribution pattern of vegetation water use in the meadow ecosystem is not very ideal at present, and water-carbon processes would gradually become imbalanced in the long run. The research results will provide a reference for sustainable water resource utilization in semi-arid areas through ecohydrological processes.