How do precipitation events modify the stable isotope ratios in leaf water at Lhasa on the southern Tibetan Plateau?

ABSTRACT

Serving as a medium between source water and cellulose, leaf water contributes to the isotope ratios (δ¹⁸O, δ²H) of plant organic matter, which can be used for paleoclimate reconstruction. This study is the first to examine the diurnal variations in the δ¹⁸O and δ²H of leaf water on the southern Tibetan Plateau. The δ¹⁸O and δ²H of leaf water were relatively low when precipitation events occurred. In particular, ¹⁸O and ²H of leaf water became extremely depleted 5 h after the precipitation event. Our findings demonstrate that precipitation can modify the isotope ratios of leaf water from external and internal causes. First, precipitation events affect meteorological elements, lead to decreases in leaf transpiration, and immediately weaken the isotope enrichment of leaf water (‘rapid effect’ of precipitation). Second, precipitation events affect the internal plant–soil water cycle process, causing the plant to preferentially use deeper soil water, and the corresponding isotope ratios of leaf water exhibit extremely low values 5 h after precipitation events (‘delay effect’ of precipitation). This study suggests that researchers need to be cautious in separating the signals of precipitation and hydrological processes when interpreting isotope records preserved in tree-ring cellulose archives from the Tibetan Plateau.

KEYWORDS:

• Hydrogen-2
• isotope ecology
• isotope ratio
• Lhasa
• leaf water
• oxygen-18
• precipitation events
• soil water
• southern Tibetan Plateau

Acknowledgements

Thanks go to Lucas Cernusak (James Cook University) for his valuable discussions and comments on the original draft. We also thank Lide Tian (Yunnan University) for providing water vapour isotopic data. Special thanks are given to two anonymous reviewers for their constructive comments and suggestions.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the National Key R&D Program of China (grant number 2017YFA0603303), National Natural Science Foundation of China (grant number 41988101–03 and 42171122).