Research Background
The hydrological processes of plants in forest ecosystems of arid regions are an essential component of regional water cycles. They not only influence community structure, ecological functions, and productivity but also affect the regional balance of matter and energy. As the primary source of water input into arid ecosystems, precipitation exhibits significant seasonal variability and limited temporal availability. The coniferous forests at the northern foothills of the Tianshan Mountains represent a typical cool-temperate forest characterized by relatively abundant rainfall during spring and summer, a long and frigid winter with substantial snowfall and prolonged snow cover, thus forming a unique seasonal pattern of water supply. However, under this spatiotemporal precipitation regime, the relative extent to which plants rely on summer rainfall versus winter-sourced moisture during the growing season remains unclear.
Based on this, the research team led by Professor Chang Shunli from Xinjiang University, in collaboration with teams from the Xinjiang Production and Construction Corps and other institutions, took the species Berberis heteropoda and Cotoneaster melanocarpus growing on the northern slopes of the Tianshan Mountains as their study objects. Using stable isotope techniques, they analyzed the contributions of seasonal precipitation to soil recharge and shrub water use, providing data support for understanding the water-use strategies of mountain forests in arid regions and their responses to climate change. The relevant findings have been published in the journal 《Journal of Hydrology: Regional Studies》.
Figure 1. Location of the study area and sampling plots. a is an overview map of China and the Tianshan Mountains; b is Urumqi County, where the study area is located; c shows the locations of the five study plots.
Research Methodology
Experimental Design: The study was conducted at the Tianshan Forest Ecosystem Research Station. Five replicate plots were established, and Berberis heteropoda and Cotoneaster melanocarpus were selected as the study objects.
Sampling: The team collected 300 soil samples in stratified fashion from April to September 2021, 100 plant branch samples from May to September, and gathered 183 rain and snow samples from January 2019 to September 2021.
Soil sampling was conducted at depths of 0–10, 10–20, 20–40, 40–70, and 70–100 cm to determine soil moisture content as well as δ²H and δ¹⁸O values in different water samples.
It is worth noting that researchers used the LI-2100 Automated Vacuum Water Extraction System(Beijing LICA United Technology Limited) to extract soil water and xylem water. This equipment operates on the principle of ultra-low-pressure vacuum distillation and freezing, enabling not only highly efficient recovery of soil water but also precise control over the extraction process, thereby preventing isotope fractionation caused by evaporation and ensuring the accuracy of hydrogen and oxygen isotope analysis results.
Data Analysis: Seasonal Origin Index (SOI) was employed to identify the seasonal origins of soil water and plant water. LC-Excess was utilized to assess soil water evaporation fractionation. Combined with variance analysis, Tukey's multiple comparisons, and correlation analysis, the seasonal variations in precipitation recharge depth and the water sources of two shrub species were analyzed.
Figure 2. Seasonal variations in precipitation, δ¹⁸O and δ²H composition of precipitation, and daily temperature in the study area from October 2019 to September 2021.
Figure 3. Monthly differences in soil moisture content by weight and soil water δ¹⁸O and δ²H isotopic compositions in the vertical soil profile (0–100 cm) of montane shrub communities from April to September 2021.
Figure 4. Comparison of seasonal dynamics of soil moisture SOI in shallow and deep layers during the growing season in 2021 in the study area.
Figure 5. Distribution of seasonal source index (SOI) of xylem water in Cotoneaster acicularis and Berberis heterophylla within the study area.
Key findings
(1) In the study area, annual precipitation in 2020–2021 was 415 mm and 446 mm, respectively. Although precipitation is concentrated in spring and summer, winter precipitation still has a significant impact on soil moisture during the growing season.
(2) In April, snowmelt significantly increased soil moisture content, allowing water to percolate down to a depth of 40 cm. SOI results indicate that meltwater from winter snowpack is the primary source of soil moisture in early spring.
(3) In May, spring rainfall mixes in, with the SOI value ranging between -0.5 and 0—this represents a mixture of “snowmelt water plus rainwater.”
(4) Summer rainfall primarily replenishes the topsoil layer from 0 to 20 cm and mixes with the pre-existing soil water. In contrast, soil moisture at depths of 40 to 100 cm remains relatively stable and continues to reflect the recharge characteristics of winter and spring precipitation.
(5) Both shrubs primarily rely on winter precipitation and a mixed winter-spring water source. However, Berberis heterophylla is more dependent on winter snowmelt water, while Cotoneaster melanocarpus exhibits more stable utilization of the mixed water source.
Conclusion
Research indicates that winter meltwater and spring rainfall serve as crucial water sources for sustaining shrub growth in the Tianshan Mountains and alleviating water stress during summer. The LI-2100 Automated Vacuum Water Extraction System provides reliable sample pretreatment support for stable isotope analysis of soil water and plant xylem water, aiding researchers in more accurately tracing water sources and analyzing plant water use strategies.
Journal：Journal of Hydrology: Regional Studies [Impact Factor: 5.6]
Research institutions: Xinjiang University, Institute of Environmental Protection Science of the Xinjiang Production and Construction Corps, and others
Study site: Tianshan Forest Ecosystem Research Station
Equipment used: LI-2100 Automated Vacuum Water Extraction System
DOI: https://doi.org/10.1016/j.ejrh.2026.103742