Integrated stomatal-wax traits confer sustained tolerance of Pistacia weinmanniifolia to prolonged dry-heat environment

Compound drought-heat events are becoming the dominant driver of tree mortality under rapid climate change. However, the functional-trait syndromes that allow woody species to survive prolonged dry-heat stress remain unresolved. We quantified leaf morphology, photosynthetic pigments, stomatal architecture, and wax micro-morphology and chemistry in Pistacia weinmanniifolia populations inhabiting three contrasting climates in south-western China: (i) dry-heat (the dry-hot valley in Jisha River, JSR), (ii) humid-heat (the tropical rainforest in Xishuangbanna Tropical Botanical Garden, XSBN), and (iii) an intermediate transitional site (the evergreen broadleaf forest in Chengjiang, CJ). Compared with plants grown in XSBN, JSR plants displayed a 60% lower specific leaf area, 44–60% lower chlorophyll content, a 36% higher carotenoid-to-chlorophyll ratio, a 65% larger individual stomatal area without altered stomatal density, a 198% increase 1-Octacosanol coverage, which dominates in platelet-like wax crystals. The data reveal a coordinated stomatal-wax strategy: enlarged, but not more numerous, stomata facilitate heat dissipation, while a highly reflective, alcohol-rich wax layer reduces radiative load and cuticular transpiration. This functional integration explains the exceptional tolerance of P. weinmanniifolia to sustained dry-heat extremes and provides a mechanistic framework for predicting species persistence under future compound climate stresses. • Investigating plant dry-heat adaptation strategies through three climatic gradients. • Plants employ a integrated “cool-save-protect” strategy to cope with combined dry-heat stress. • Increasing the stomatal size rather than density can enhance heat dissipation efficiency. • The formation of wax crystals reduces solar absorptance to cool the leaves; • Wax crystals minimize water loss, while compositional changes enhance the capture of water vapor.