Yang Qingqing, Zhang Zijing, Zhang Hui, Yang Huai, Pandey Shree, John Robert
School of Ecology, Hainan University, Haikou, China.
Hainan Academy of Forestry (Hainan Academy of Mangrove), Haikou, China.
Front Plant Sci. 2024 Oct 17;15:1488163. doi: 10.3389/fpls.2024.1488163. eCollection 2024.
Tropical cloud forest ecosystems are expected to face reduced water inputs due to climatic changes.
Here, we study the ecophysiological responses of trees and epiphytes within in an Asian cloud forest to investigate the contributions of rainfall, fog, and soil to leaf water in 60 tree and 30 vascular epiphyte species. We measured multiple functional traits, and δH, and δO isotope ratios for leaf water, soil water, rainfall, and fog in the wettest (July) and driest (February) months. Using a Bayesian stable isotope mixing model, we quantified the relative contributions of soil water, fog, and rainfall to leaf water.
Rainfall contributes almost all the leaf water of the epiphytes in July, whereas fog is the major source in February. Epiphytes cannot tap xylem water from host trees, and hence depended on fog water when rainfall was low. Most of leaf water was absorbed from soil water in July, while fog was an important source for leaf water in February despite the soil moisture content value was high. In February, lower temperatures, along with reduced photosynthesis and transpiration rates, likely contributed to decreased soil water uptake, while maintaining higher soil moisture levels despite the limited rainfall. These contrasting contributions of different water sources to leaf water under low and high rainfall and for different plant groups outline the community-level ecophysiological responses to changes in rainfall. While direct measurements of water flux, particularly in roots and stems, are needed, our results provide valuable insights on tropical cloud forest hydrology under scenarios of decreased fog immersion due to climatic changes.
由于气候变化，热带云雾森林生态系统预计将面临降水减少的情况。
在此，我们研究了亚洲云雾森林中树木和附生植物的生态生理响应，以调查降雨、雾和土壤对60种树木和30种维管束附生植物叶片水分的贡献。我们在最湿润的月份（7月）和最干燥的月份（2月）测量了多种功能性状以及叶片水、土壤水、降雨和雾中的δH和δO同位素比率。使用贝叶斯稳定同位素混合模型，我们量化了土壤水、雾和降雨对叶片水的相对贡献。
7月降雨几乎贡献了附生植物的所有叶片水分，而2月雾是主要来源。附生植物无法从寄主树木的木质部获取水分，因此在降雨较少时依赖雾水。7月大部分叶片水分从土壤水中吸收，而2月尽管土壤含水量较高，雾仍是叶片水分的重要来源。2月，较低的温度以及光合作用和蒸腾速率的降低，可能导致土壤水分吸收减少，尽管降雨量有限，但土壤水分水平仍保持较高。不同水源在降雨高低不同情况下对不同植物群体叶片水分的这些不同贡献，概述了群落水平对降雨变化的生态生理响应。虽然需要直接测量水分通量，特别是在根和茎中，但我们的结果为气候变化导致雾浸减少情况下的热带云雾森林水文学提供了有价值的见解。
