Transpiration rates decline under limited moisture supply along hillslopes in a humid karst terrain

Wenna Liu; Yunpeng Nie; Zidong Luo; Zhongyun Wang; Li Huang; Fei He; Hongsong Chen

doi:10.1016/j.scitotenv.2023.164977

Transpiration rates decline under limited moisture supply along hillslopes in a humid karst terrain

Sci Total Environ. 2023 Oct 10:894:164977. doi: 10.1016/j.scitotenv.2023.164977. Epub 2023 Jun 20.

Authors

Wenna Liu¹, Yunpeng Nie², Zidong Luo², Zhongyun Wang¹, Li Huang¹, Fei He³, Hongsong Chen⁴

Affiliations

¹ Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan 410125, China; Guangxi Key Laboratory of Karst Ecological Processes and Services, Huanjiang Observation and Research Station for Karst Ecosystems, Chinese Academy of Sciences, Huanjiang, Guangxi 547100, China; University of Chinese Academy of Sciences, Beijing 100039, China.
² Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan 410125, China; Guangxi Key Laboratory of Karst Ecological Processes and Services, Huanjiang Observation and Research Station for Karst Ecosystems, Chinese Academy of Sciences, Huanjiang, Guangxi 547100, China.
³ Guangxi Key Laboratory of Karst Ecological Processes and Services, Huanjiang Observation and Research Station for Karst Ecosystems, Chinese Academy of Sciences, Huanjiang, Guangxi 547100, China.
⁴ Key Laboratory of Agro-ecological Processes in Subtropical Region, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Changsha, Hunan 410125, China; Guangxi Key Laboratory of Karst Ecological Processes and Services, Huanjiang Observation and Research Station for Karst Ecosystems, Chinese Academy of Sciences, Huanjiang, Guangxi 547100, China. Electronic address: hbchs@isa.ac.cn.

PMID: 37348725
DOI: 10.1016/j.scitotenv.2023.164977

Abstract

Topographic positions can mediate subsurface water availability, but its effects on tree transpiration are controversial. In humid karst regions, climax forests are usually not limited by moisture supply, even at the summit, through absorbing water from deep layers. However, little is known on the transpiration pattern and its limiting factor on the shrubland widely distributed along the karst hillslopes. In the current study, Rhus chinensis, a widely spread constructive species in natural restoration was selected. Meteorological factors, 0-300 cm soil-epikarst moisture, sap flow, and root water uptake were studied during an entire growing season to assess how hillslope positions affected transpiration. We found the mean water content in uphill was only around 60 % of that in downhill, indicating a contrasting water supply along the slope. However, there were no significant differences in the xylem isotopic composition and lc-excess which suggested the similar water uptake strategies in both uphill and downhill. R. chinensis primarily relied on the soil water rather than epikarst water (groundwater) along the hillslope because of the MixSIAR model results and more negative lc-excess values (-13.18 ‰). R. chinensis exhibited decreases of nearly half in the transpiration rate and amount in uphill compared to those in downhill. In downhill with sufficient water availability, transpiration followed the variation in atmospheric water demand. In uphill, a poor moisture supply limited tree transpiration and its response to atmospheric water demand. Our findings revealed that the early successional species did not entirely depend on atmospheric water demand, absorbing deep epikarst water as the mature forest. The transpiration rates of those species declined by nearly half to adapt to the water-limited environment along the hillslope in the humid karst region. This study can contribute to the evaluation of eco-hydrological functions during natural restoration.

Keywords: Karst ecosystem; Plant water source; Stable isotope; Transpiration; Water–limitation.