The unexplored direct response of leaf stomata to temperature (DRST): patterns, mechanisms and impacts

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Plants provide all the energy used by life on land, by taking CO2 from the air and using energy from the sun to turn it into sugar. During this process, water evaporates from leaves. In fact, most of the water that falls as rain returns to the atmosphere after evaporating from leaves. It is essential to understand how plants regulate water loss, both to identify which genes control that regulation, so that breeders can improve crop water use efficiency, and also to enable accurate predictions of how fluctuating weather and climate will affect water loss from crops, rangelands, and forests. Plants regulate water loss by opening and closing pores on the surfaces of leaves – for example, they open in sunlight, and close when soil is dry. However, little is known about how changes in temperature affect these pores. This study will determine those effects for 60 species, selected to represent most major habitats on Earth; test hypotheses for the biological causes of any temperature responses that are discovered; and incorporate these discoveries in a computer model to predict how temperature responses affect plant growth and water loss. In addition to training of undergraduate and graduate students in modern experimental plant biology, an experiential project will be developed in which students from a nearby high school with a large population of underprivileged students, will build outdoor growth chambers spanning a range of different temperatures. These chambers will allow students to observe firsthand how even small differences in temperature can have dramatic effects on plant growth and yield. Little is known about stomatal responses to temperature, although it is well-documented that temperature affects stomata indirectly via the leaf-to-air vapor pressure difference (VPDleaf). VPDleaf increases rapidly as leaves warm due to rising saturation vapor pressure in the leaf airspaces, causing stomata to close. But the direct response of stomata to temperature (DRST) – the response to temperature when VPDleaf is held constant – has rarely been reported for intact leaves, leaving the underlying mechanisms and ecological diversity largely unknown. Lack of knowledge of the DRST may skew models of carbon and water flux, preventing accurate prediction and understanding of plant function in a warming world. This study will quantify the DRST and its acclimation to growth temperature in species spanning the world's major functional types and ecosystems, plus 10 species and cultivars from a diverse, cosmopolitan clade (the genus Vitis); test predicted adaptive, biogeographic, and evolutionary trends in the DRST; test major hypothetical mechanisms for the DRST and use the results to refine a mechanistic model of stomatal conductance; and apply the resulting knowledge to a functional-structural 3D canopy model to quantify how the DRST affects integrated carbon and water fluxes at a range of time scales.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.