Research Background
In karst regions, the soil layer is shallow and bedrock is often exposed. Groundwater distribution varies significantly across different soil layers and rock fractures, making water availability a critical factor limiting vegetation restoration and long-term stability. Limestone and dolomite differ markedly in terms of weathering degree, soil thickness, and fracture structure, which may further influence plant root water uptake, xylem water transport, and leaf transpiration processes. However, existing studies have largely focused on the impacts of climate or vegetation type on plant water use. There remains a significant lack of quantitative understanding regarding how rock lithology—by altering the pattern of water supply—systematically drives the reshaping of the entire continuous water-use strategy encompassing root water uptake, xylem transport, and leaf transpiration.
In response to this issue, the research team led by Professor Chen Hongsong from the Institute of Subtropical Agriculture and Ecology, Chinese Academy of Sciences, conducted a systematic study on five common native tree species found in karst limestone and dolomite habitats in southwestern China. Using techniques such as stable isotope tracing and embolism vulnerability curves, they determined the sources of root water uptake, xylem hydraulic traits, and leaf C/O isotopes. The findings provide a theoretical basis for vegetation restoration in heterogeneous karst environments. This research was published in "Tree Physiology."
Figure 1. Hydraulic characteristics, karst ecosystems, stable isotopes, stomatal regulation, water sources.
Research Methodology
The study was conducted in two small watersheds—limestone and dolomite—in the northwest of the Guangxi Zhuang Autonomous Region. Four 20 m × 20 m plots were established in each of the two lithological habitats, totaling eight plots. Five common deciduous tree species—namely, Rhus chinensis, Sophora japonica, Ziziphus mauritiana, Albizia lebbeck, and Toona sinensis—which are found in both limestone and dolomite habitats were selected to minimize the interference of differences in tree species composition on the study results.
Monitoring indicators: soil water content, soil water δD and δ¹⁸O, xylem water δD and δ¹⁸O, contribution proportions of water sources from different soil layers, main water uptake depth of plants, xylem water potential, hydraulic conductivity, wood density, as well as leaf δ¹³C and δ¹⁸O, etc.;
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: The MixSIAR model was used to estimate the contribution of water sources from different soil layers. Variance analysis, regression analysis, and linear mixed models were employed to compare differences among various rock types and tree species, and to elucidate the synergistic and trade-off relationships among root, xylem, and leaf water traits.
Figure 2. Average proportion of water use by species (± standard deviation): (a) rainy season; (b) dry season
Figure 3. Cavitation vulnerability curves of terminal branches of various tree species in limestone and dolomite artificial forests.
Figure 4. Seasonal variations in isotopic values of leaves in limestone and dolomite plantations: (a) δ¹³C and (b) δ¹⁸O (± SD).
Figure 5. Correlation among key plant water use traits in the root-xylem - leaf continuum.
Research results
Limestone trees primarily rely on deep soil water, whereas dolomite trees depend more on shallow water sources; this difference is mainly determined by rock type rather than tree species.
Limestone plants tend to have efficient water transport, while dolomite plants enhance hydraulic safety by increasing wood density and improving resistance to embolism.
Limestone plants exhibit a more liberal stomatal regulation and higher water-use efficiency, whereas limestone plants employ a conservative strategy with tightly regulated stomata and lower water consumption.
Plants that rely on shallow water sources exhibit higher hydraulic safety, while those that tap into deeper water sources experience weaker stomatal limitations, thus giving rise to an “acquisitive” strategy in limestone habitats and a “conservative” strategy in dolomite habitats.
Conclusion
From a single rock to an entire forest, bedrock may seem silent, yet it profoundly influences how plants locate, transport, and conserve every drop of water. The distinct water-use strategies that have evolved in limestone and dolomite habitats remind us that vegetation restoration in karst regions cannot focus solely on tree species—rather, we must also gain a deep understanding of the underlying geological and soil conditions beneath our feet. As long-term observations and studies of extreme droughts continue to deepen, we will further uncover the stability of these strategies in the face of climate change, enabling us to select tree species better suited to different rock types and ensuring that restored forests not only take root firmly but also thrive for the long term.
Journal of Publication: Tree Physiology [Impact Factor: 4.0]
Research institutions: Institute of Subtropical Agriculture, Chinese Academy of Sciences; Key Laboratory of Karst Ecological Processes and Services, Guangxi, Chinese Academy of Sciences, and others.
Study site: Huanjiang Karst Ecosystem Observation and Research Station, Chinese Academy of Sciences
Equipment used:LI-2100 Automated Vacuum Water Extraction System
DOI: https://doi.org/10.1093/treephys/tpag013