Researchers Assess Hydraulic Redistribution in Different Soil Layers and Analyze the Impact of Populus euphratica Root on Hydraulic Redistribution in the Lower Reaches of the Tarim River

Hydraulic redistribution by plant roots can improve the quantity of water available in soil, delay embolism formation in plant roots, and enhance the nutritional status of deeply rooted plants during dry periods. One of the major issues related to hydraulic redistribution is assessment of the quantity of redistributed water. Many studies based on general statistical analysis of the observed soil water content or soil water potential data have been reported, but they only provided a rough estimate of the amount of hydraulically redistributed water (HRW) and failed to consider the unsaturated water flow in soil. Therefore, the use of models to simulate HRW has become a very effective method of analysis.

An effective assessment method of hydraulic redistribution and HRW is stable isotope (e.g., δ¹⁸O and δ²H) sampling and analysis. The stable isotope method has been widely used in hydraulic redistribution, and it has revealed characteristics of hydraulic redistribution under different habitats and climatic conditions.

The roots of Populus euphratica exhibit a significant level of hydraulic redistribution in the lower reaches of the Tarim River, Northwest China. However, quantitative assessments of the water-sharing process and its ecological effects are limited. Therefore, Dr. HAO Xingming et al. used an assessment model based on field observation parameters, including soil water content (soil water potential), root distribution, and stable isotope δ¹⁸O values of soil and plant samples during the entire growing season of 2011 to quantitatively assess hydraulic redistribution in different soil layers and analyze the impact of P. euphratica root on hydraulic redistribution.

The result showed that hydraulic redistribution in P. euphratica can be detected in 0–120 cm soil layers, with the amount of HRW in the soil found at different depths as follows: 60–80>40–60>20–40>0–20>80–100>100–120 cm. The variations in HRW in soil layers can be partly attributed to the vertical distribution of roots. The denser roots found at greater depths positively influenced the amount of redistributed water in lower soil layers. During the growing season, the amount of HRW reached a daily average of 0.27 mm, which allowed increased transpiration and provided an adequate water supply to herbs. Based on the stable isotope (δ¹⁸O) data, the amount of HRW provided by the roots of P. euphratica could meet 22%–41% of its water demand. The result was published in Environmental Monitoring and Assessment in December 2013.