Evaluating abnormalities in daily transpiration patterns across tree species in a semi-arid climate




McLaughlin, Jack Riley

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Climate change causes shifts in precipitation, temperature, shifting climate zones and more, thus affecting the ecology and hydrologic feedbacks of many environments, specifically those existing in already warm, arid climates. Vegetation affects the local hydrologic cycle, as it promotes multiple feedback mechanisms, such as the extraction of soil water via roots, the re-wetting of the atmospheric boundary layer and lowering temperatures through transpiration. This study focuses on transpiration patters in a hot semi-arid environment, which is defined as having a total annual precipitation between one-fifth and one-half of potential evapotranspiration and an annual mean temperature above 18°C. Meteorological conditions, sap flow, leaf water potential, carbon assimilation, and stomatal conductance were all recorded during 2021 in order to observe the drivers of transpiration among ashe juniper, lacey oak and pinyon pines, along with abnormalities in their diurnal sap flow patterns, where the majority of sap flow occurs at dawn and dusk instead of midday. Sap flow was shown to increase in magnitude (up to 350% in pinyon pines’ case) when environmental conditions such as vapor pressure deficit (VPD), temperature and soil water potential (SWP) are favorable. Ashe juniper was found to have a weak relationship between leaf water potential (LWP) and VPD, along with a stronger relationship between LWP and SWP. Oaks were found to have a very strong relationship between LWP and VPD, while pines were found to have a weak relationship between LWP and VPD. Of the three species, only the oaks were found to have a relationship between carbon assimilation rates and VPD, carbon assimilation rates and SWP, and stomatal conductance and SWP. This makes oaks the most vulnerable of the three species to future climate change and shifting climate zones. Better understanding of plant responses to stressful climatic conditions and in arid environments will provide insight in plant durability and adaptations to a warming climate, all of which are important as our global and local climates continue to change


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