As Earth’s climate changes, it is impacting extreme weather across the planet. Compound drought-heat events have become key drivers of global tree mortality. However, it remains poorly understood how woody plants coordinate their functional traits to endure chronic dry-heat conditions.

In a study published in Plant Physiology and Biochemistry, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) of the Chinese Academy of Sciences and their collaborators investigated the adaptive strategies of Pistacia weinmanniifolia, and revealed the biological mechanisms underlying the species’ sustained tolerance to prolonged dry-heat stress.

Pistacia weinmanniifolia is an evergreen hardy tree species distributed across three climatically distinct regions in Yunnan Province. Researchers compared the populations from a prolonged dry-heat valley, a humid-heat tropical rainforest, and an intermediate transitional zone, and detailed the precise anatomical and chemical adjustments that enable the species to decouple leaf temperature from scorching ambient conditions.

Researchers systematically analyzed leaf morphology, photosynthetic pigment content, and the structure and chemical composition of the leaf epidermal wax layer. The findings revealed a sophisticated, two-pronged adaptive strategy involving the coordinated regulation of stomata and epicuticular waxes to cope with dry-heat stress.

In the extreme dry-heat environment, leaves of Pistacia weinmanniifolia exhibited significantly lower specific leaf area and reduced photosynthetic pigment content compared to those in humid and transitional environments.

Under dry-heat stress, the trees did not alter the density of their stomata, but significantly increased individual stomatal area. This optimized the leaf's ability to cool itself through transpiration without creating excessive vulnerabilities for water loss. Meanwhile, by boosting the synthesis of specific alcohol-based waxes, the trees build a protective barrier that reflects light and reduces water loss.

The combination of these traits underpins the species' remarkable tolerance to extreme, prolonged dry-heat conditions.