Their review, Leaf temperature and its departure from ambient air temperature<\/em><\/a>, synthesizes global observations across climates, ecosystems, and measurement scales to reveal how plants regulate heat, and why current models may be missing one of the most important pieces of the puzzle: leaf temperature<\/p>\n <\/p>\n Leaf temperature is the temperature at the leaf surface, where plants exchange both carbon and water with the atmosphere. This is where photosynthesis happens, where transpiration cools the plant, and where heat stress can damage tissues.<\/p>\n Although leaf temperature is closely linked to air temperature, the two can differ substantially .<\/p>\n In some dry, sunny environments, leaf temperatures can exceed air temperature especially in exposed canopy-top leaves. In tropical forests, leaves can reach dangerous temperatures of nearly 50\u00b0C, approaching thresholds where irreversible damage occurs.<\/p>\n This difference between leaf and air temperature, known as \u0394T (delta T), depends on how much heat a leaf absorbs and how effectively it can cool itself.<\/p>\n Plants cool leaves through:<\/strong><\/p>\n Plants warm leaves through:<\/strong><\/p>\n This balance determines whether a leaf stays safe or if it overheats.<\/p>\n It\u2019s long been debated if plants actively regulate the temperature of their leaves. This thermoregulation capacity is often assessed by measuring how leaf temperature changes relative to air temperature. We know that there are three main patterns discussed in literature:<\/p>\n Using a global synthesis of 180 observations across different biomes, Xu Lian et al., found that all three patterns occur\u2014but where and when they occur depends strongly on the background climate.<\/p>\n Warm ecosystems tend toward megathermy<\/strong><\/p>\n In warm tropical forests and dry environments, especially in sun-exposed canopy-top leaves, plants often show megathermy\u2014leaf temperatures rise faster than air temperature because excess solar radiation cannot be dissipated efficiently.<\/p>\n Cold ecosystems show more homeothermy<\/strong><\/p>\n In colder ecosystems or shaded sub-canopy leaves, plants more often show limited homeothermy, where leaves remain buffered against rapid air temperature changes.<\/p>\n Leaf temperature responses differ across climate zones, canopy position, measurement method, time of day and water availability. This means that the long-standing debate over whether plants thermoregulate may actually depend on where<\/em> and how<\/em> we measure temperature. In short: there is no single global thermoregulation strategy.<\/p>\n <\/p>\n If you\u2019ve been following our blog for a while, you will know a lot of our research focuses on stomatal regulation of carbon uptake (for photosynthesis) and water loss (through transpiration). But one of the most important insights from the review is that stomata may be actively regulating temperature as well.<\/p>\n Most current stomatal theories assume plants optimize a trade-off between carbon gain vs. water loss. But under heat stress, particularly when water is not a major concern, that may not be enough to explain the stomatal behaviour.<\/p>\n The review shows that when temperatures become dangerously high, some plants, especially warm-adapted species, keep stomata open even when photosynthesis has largely stopped.<\/p>\n Why?<\/p>\n Because transpiration helps cool the leaf. Plants may choose to lose water to avoid overheating.<\/p>\n This creates a third optimization target:<\/p>\n Carbon gain + Water conservation + Thermal safety<\/strong><\/p>\n This \u201ctriple-target optimization\u201d<\/strong> challenges the foundations of many current stomatal models.<\/p>\n For example, during extreme heatwaves, well-watered trees have been observed maintaining high stomatal conductance simply to keep leaves cooler, even at the cost of increased hydraulic risk. Traditional stomatal models based only on carbon-water trade-offs cannot explain this behaviour.<\/p>\n <\/p>\n This has major implications for how we model photosynthesis and predict future carbon uptake.<\/p>\n Most land surface models still simplify leaf temperature by using air temperature as a proxy, assuming stomata respond only to carbon and water economics and neglecting vertical temperature differences within canopies.<\/p>\n These simplifications can create large errors in predicted photosynthesis, transpiration, and carbon sequestration.<\/p>\n For example: Elevated CO\u2082 often reduces stomatal opening, which improves water-use efficiency. But smaller stomatal opening also means: Less evaporative cooling \u2192 hotter leaves \u2192 greater heat stress<\/p>\n This is especially concerning for tropical forests, where many species already operate close to their thermal limits. Without explicitly representing leaf temperature, models may underestimate heat stress and overestimate future carbon uptake.<\/p>\n <\/p>\n <\/p>\n This review also highlights the need for better observations. Different methods capture different thermal signals:<\/p>\n This might explain why studies sometimes report conflicting thermoregulation patterns. What we need, maybe slightly ambitiously, is a globally coordinated observation system using a combination of the three along with co-located measurements of stomata, sap flow and plant traits. This is one reason why we have a big emphasis on experimental measurements as a core part of the LEMONTREE project.<\/p>\n Studies show that as temperatures rise, plants can shift their thermal tolerance thresholds upward. But this acclimation is often insufficient and there is a limit.\u00a0 Typically, critical temperature limits increase by less than 0.4\u00b0C for every 1\u00b0C of warming<\/strong>.<\/p>\n This means that as warming accelerates, plants may run out of thermal safety margin and tropical species may be especially vulnerable, as many already live near their upper thermal limits and show limited capacity for further acclimation.<\/p>\n Once critical thresholds are crossed, it can trigger severe physiological damage to the leaves and reduced carbon uptake.<\/p>\n <\/p>\n This review paper makes a powerful case that leaf temperature, not air temperature, should be central to plant ecology and climate prediction.<\/p>\n It shows that plants are not simply passive to warming. They actively regulate temperature through coordinated changes in physiology, especially stomatal behaviour.<\/p>\n However, under future climate extremes, that regulation may fail.<\/p>\n To predict ecosystem responses accurately, models must move beyond simple carbon-water trade-offs and include the full reality of plant thermoregulation:<\/p>\n Carbon, Water, and<\/em> Heat.<\/strong><\/p>\n <\/p>\n <\/p>\n For more details, see the full paper in Nature Plants<\/em>.<\/p>\n Lian, X., Jiji, J., Fang, J., Han, J., Ryu, Y., Harrison, S.P., Jeong, S., Zhang, H., Novick, K., Benson, M.C., Dong, N., Green, J.K., Sandoval, D., Jiu, J., Keenan, T.F. & Gentine, P. (2026). Leaf temperature and its departure from ambient air temperature. Nature Plants. https:\/\/doi.org\/10.1038\/s41477-026-02304-w<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"Leaves Are Often Much Hotter Than the Air Around Them<\/h2>\n
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Do Plants \u201cThermoregulate\u201d?<\/h2>\n
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Stomata Are Doing More Than Saving Water<\/h2>\n
Why This Matters for Climate Models<\/h2>\n
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From Leaf to Canopy: Measuring Temperature Better<\/h2>\n
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Can Plants Keep Up With Warming?<\/h2>\n
Final Thoughts<\/h2>\n