关键词: 热带雨林, 林冠塔吊, 稳定同位素, 水分来源, 水分利用效率

Abstract: Aims Parashorea chinensis is one of the most representative dominant tree species in tropical rainforests of China. It plays an important ecological role in maintaining the structure and function of tropical rainforests. With the intensification of global climate change and human disturbance, its habitat fragmentation has increased and populations have shown a declining trend. Clarifying water-use strategies across developmental stages is essential for understanding the ecological adaptation ofP. chinensis. It is also important to determine how this species responds to seasonal soil moisture stress./t/nMethods Utilizing the canopy crane platform in the tropical seasonal rainforest of Xishuangbanna, Yunnan, this study selected Parashorea chinensis individuals at three growth stages (adult trees, medium trees, and seedlings) for a year field observation. Stable hydrogen and oxygen isotopes (δ²H andδ¹⁸O) of xylem water and potential water sources was used to estimate the contribution proportions of water from various soil depths. Concurrently, leaf carbon stable isotopes (δ¹³C) along with leaf predawn (Ψ_pd) and midday (Ψ_md) water potentials were integrated to comprehensively evaluate the physiological regulatory characteristics of the species./t/nImportant findings The result showed that allP. chinensis primarily relied on 0-30 cm soil water, while the proportional contributions of soil layers differed significantly among different growth stages.Adult trees mainly utilized water from the 10-30 cm soil water and exhibited a transient enhancement in deep water uptake at the onset of the rainy season. Medium sized trees concurrently exploited soil water from both the 0-10 cm and 10-30 cm soil water layers, maintaining a relatively stable water source structure across seasons. In contrast, seedlings relied almost exclusively on 0-10 cm surface soil water and showed no pronounced seasonal shift in their water sources. As trees transitioned from the seedling to the adult stage, leaf δ¹³C values increased while leaf water potentials decreased, indicating stronger stomatal limitation and higher intrinsic water use efficiency (WUE_i) in adult trees. Our comprehensive analysis suggests a coordinated shift in water uptake depth and water use efficiency across developmental stages. Specifically, seedlings depended primarily on shallow soil water and maintained low WUE_i, while adults showed greater reliance on deeper water sources together with increased WUE_i. Our results incicated that P. chinensis exhibited distinct variations in water-uptake depth and physiological responses. It helps explain how dominant tropical rainforest trees cope with seasonal water fluctuations and provides a scientific basis for P. chinensisconservation and management.

Key words: tropical rainforest, canopy crane, stable isotopes, water source, water-use efficiency