Water use strategies of natural Pinus sylvestris var. Mongolica trees of different ages in Hulunbuir Sandy Land of Inner Mongolia, China, based on stable isotope analysis
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Natural Mongolian pine trees of different ages consistently use shallow water throughout the main growing season; therefore, water stored in the shallow soil layer is vital for maintaining their viability.
Mongolian pine (Pinus sylvestris var. mongolica) plantations in sandy regions often experience dieback after 30–35 years of growth due to water deficiency, whereas natural Mongolian pine forests remain healthy during the same growth stage. However, the water use strategies of natural Mongolian pines remains unclear. Therefore, δ2H and δ18O in twig xylem water, soil water and groundwater were analyzed in 10–20, 20–30 and 30–50-year-old natural Mongolian pine trees to identify their water sources. In addition, needle δ13C was measured simultaneously to assess water use efficiency. Results showed that pine trees of different ages utilized soil water from the same depth. During the growing season (June–August), all pine trees utilized water from 0 to 20 cm soil depth, regardless of the soil water condition. During the end of growing season (September and October), even though soil moisture content in the 0–20 cm depth was higher, pine trees of different ages utilized water from the 0–60 cm soil depth in September and switched to utilize water from the 20–80 cm soil depth in October. There were no significant differences in needle δ13C among the sampling dates for trees in each age group, indicating that pine trees can absorb sufficient water to satisfy their water requirements regardless of age. These findings suggest that water stored in the shallow soil layer (0–20 cm) plays an important role in supporting tree transpiration during the growing season (June–August). Therefore, the stability of shallow soil is vital for maintaining the viability of natural Mongolian pine forests.
KeywordsStable isotopes Deuterium and oxygen isotopic composition Carbon isotopic composition Soil water content Groundwater
This research was supported by Grants from the Key Research Program of Frontier Sciences, CAS (QYZDJ-SSW-DQC027) and the National Nature Science Foundation of China (31770757, 41371511 and 31025007). We thank Dr. Lizhong Yu, Dr. Qiaoling Yan, Dr. Kai Yang, Dr. Xiao Zheng, Dr. Tian Gao and Dr. Yirong Sun in Division of Ecology and Management for Secondary Forest of Institute of Applied Ecology, Chinese Academy of Sciences, China for their helpful discussion on this manuscript. We also thank Yuxiang Ge, Lizhi Zhang and Xiaolin Zhang in Honghuaerji Forestry Administration of Inner Mongolia for providing help and support in the field.
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Conflict of interest
The authors declare that they have no conflict of interest.
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