Trade-offs between root water uptake and xylem-leaf water-use traits underpin contrasting plant adaptation strategies in limestone and dolomite habitats

Abstract

Plant adaptation strategies to environmental variability encompass not only climatic factors but also the underlying subsurface structure, which are critical for the sustainability of vegetation restoration. However, plant water-use traits and their relationships across varying soil-rock structure settings for common species remain unclear, undermining the reliability of adaptation assessments in heterogeneous habitats. The current study examined five common tree species from two different bedrock types-limestone and dolomite-within Southwest China. Key plant water-use traits, including root water sources, xylem hydraulic traits (P50 and wood density) and leaf stable isotopes (δ18O and δ13C) as proxies for stomatal regulation and water-use efficiency, were measured. Results revealed that the predominant root water uptake depths of all five species were significantly deeper in the limestone site (P < 0.05), with its discontinuous, deep-pocketed soil, compared with the dolomite site, where the continuous, thinner soil layer predominated. Besides, species in limestone site exhibited significantly less negative P50, lower wood density and leaf δ18O, more negative δ13C values compared with those in dolomite (P < 0.05). The study also identified significant trade-offs between root water uptake patterns, xylem hydraulic traits and leaf isotopic composition (P < 0.05). These relationships elucidate two contrasting adaptive strategies: an acquisitive strategy with high hydraulic efficiency and carbon demands, supported by a deep and stable water supply in limestone site, and a conservative strategy with high hydraulic safety and strict stomatal response, constrained by a fluctuating shallow water source in dolomite. Our findings underscore the profound influence of lithology on plant water-use traits and highlight how the trade-off of root and xylem-leaf traits improves the adaptation assessments in such fragile, heterogenous environments.

Keywords: hydraulic traits; karst ecosystem; stable isotope; stomatal regulation; water sources.