Seasonal Changes in the Water Use Strategies of Three Co-occurring Desert Shrubs

Water determines a great many ecosystem processes in arid and semiarid regions, such as carbon storage, species survivorship, competition and primary production. As the main water input in desert ecosystems, precipitation dominates water availability or water resources for plants. However, due to the uneven distribution of precipitation, soil moisture in arid ecosystems is extremely variable both in space and time.

In order to learn how plants cope with changes in water resources over time and space, it is important to understand plant–water relations in desert region. Using the oxygen isotopic tracing method, Dr. WU Yu et al. clarified the seasonal changes in the water use strategies of three co-occurring desert shrubs. During the 2012 growing season, δ¹⁸O values were measured for xylem sap, the soil water in different soil layers between 0 and 300 cm depth and groundwater. Based on the similarities in δ¹⁸O values for the soil water in each layer, three potential water sources were identified: shallow soil water, middle soil water and deep soil water. Then they calculated the percentage utilization of potential water sources by each species in each season using the linear mixing model.

The results showed that the δ¹⁸O values of the three species showed a clear seasonal pattern. Reaumuria songarica used shallow soil water when shallow layer was relatively wet in spring, but mostly took up middle soil water in summer and autumn. Nitraria tangutorum mainly utilized shallow and middle soil water in spring, but mostly absorbed deep soil water in summer and autumn. Tamarix ramosissima utilized the three water sources evenly in spring and primarily relied on deep soil water in summer and autumn. R. songarica and N. tangutorum responded quickly to large rainfall pulses during droughts. Differential root systems of the three species resulted in different seasonal water use strategies when the three competed for water.

The result was published in Hydrological Processes on 30 December 2014.