Larger changes in water use efficiency in species with less sensitive stomata

Nawatbhrist Kitudom, Hua Lin
Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China

In the past decade, Yunnan Province has experienced an increasing frequency of heatwaves, significantly impacting local ecosystems. To better understand how key species in contrasting environments—savanna and tropical rainforest—adapt to environmental stressors such as high temperatures and drought, we investigated gas exchange responses in 11 species common to both habitats. We measured net photosynthesis (Anet​), stomatal conductance (gs​), transpiration rate (E), and instantaneous water use efficiency (WUE) under a diurnal temperature gradient, alongside photosynthetic heat tolerance (T50) and turgor loss point (TLP). Our results indicate that species in the savanna prioritize water conservation, exhibiting higher WUE driven by reduced E, while tropical rainforest species likely maintain higher Anet​. Vapor pressure deficit emerged as a key factor influencing gas exchange dynamics, particularly Anet​, despite largely overlapping effects of leaf temperature. Savanna species demonstrated greater T50, though Tmax and TLP showed no significant differences between habitats. Furthermore, WUE sensitivity was closely linked to gs​ sensitivity and heat tolerance traits. These findings highlight potential shifts in carbon and water dynamics as common species adapt to hotter and drier conditions, offering important insights into ecosystem functionality under future climate scenarios.