Water Uptake Dynamics and Hydrological Niche Characteristics of Four Lianas in Xishuangbanan Tropical Rainforest

To clarify the water use patterns of lianas under the background of changing regional rainfall patterns and intensified extreme droughts, and to provide a scientific basis for understanding the drought adaptation strategies and water competition relationships of co-existing lianas in tropical rainforests. Based on the canopy crane platform and the stable hydrogen and oxygen isotopes (δ²H and δ¹⁸O) , the samples of precipitation, soil water, and xylem water were continuously collected from four common liana species (Pothos scandens, Rhaphidophora peepla, Tetracera sarmentosa, and Premna scandens) in Xishuangbanna from December 2021 to October 2022. Their water sources were quantitatively analyzed using the MixSIAR Bayesian linear mixing model, and the proportional similarity (PS) index was used to evaluate the degree of hydroecological niche overlap among co-existing lianas. The results demonstrate that: (1) Soil water content and soil water isotopic composition exhibited significant seasonal variations, which mainly occurred in the 0-30 cm soil layer, which supported the isotope-based tracking of liana water sources; (2) The four liana species mainly utilized shallow soil water (0-30 cm), with an average utilization ratio of 82.4%±13.9%, indicating that their water uptake was dominated by shallow root systems; (3) Except for Premna microphylla, the other three lianas showed a high degree of hydroecological niche overlap (PS=84.4%±2.8%) which suggested obvious interspecific water competition among three lianas. The result demonstrate that the observed lianas in Xishuangbanna tropical rainforest mainly relied on shallow soil water and exhibited distinct shallow-root characteristics. This strategy may facilitate its adaptation to seasonal droughts but also increased the risk of hydraulic failure caused by extreme droughts. In the future, it is necessary to include more species and physiological indicators to further reveal their water use mechanisms, so as to deepen the understanding of the role of lianas in the stability and diversity of tropical rainforest communities.