Plants modify the climate and provide natural cooling through transpiration. However, plant response is not only dependent on the atmospheric evaporative demand due to the combined effects of wind speed, air temperature, humidity, and solar radiation, but is also dependent on the water transport within the plant leaf-xylem-root system. These interactions result in a dynamic response of the plant where transpiration hysteresis can influence the cooling provided by the plant. Therefore, a detailed understanding of such dynamics is key to the development of appropriate mitigation strategies and numerical models. In this study, we unveil the diurnal dynamics of the microclimate of a Buxus sempervirens plant using multiple high-resolution non-intrusive imaging techniques. The wake flow field is measured using stereoscopic particle image velocimetry, the spatiotemporal leaf temperature history is obtained using infrared thermography, and additionally, the plant porosity is obtained using X-ray tomography. We find that the wake velocity statistics are not directly linked with the distribution of the porosity but depends mainly on the geometry of the plant foliage which generates the shear flow. The interaction between the shear regions and the upstream boundary layer profile is seen to have a dominant effect on the wake turbulent kinetic energy distribution. Furthermore, the leaf area density distribution has a direct impact on the short-wave radiative heat flux absorption inside the foliage where 50% of the radiation is absorbed in the top 20% of the foliage. This localized radiation absorption results in a high local leaf and air temperature. Furthermore, a comparison of the diurnal variation of leaf temperature and the net plant transpiration rate enabled us to quantify the diurnal hysteresis resulting from the stomatal response lag. The day of this plant is seen to comprise of four stages of climatic conditions: no-cooling, high-cooling, equilibrium, and decaying-cooling stages.

植物改变气候并通过蒸腾作用提供自然冷却。然而，由于风速、气温、湿度和太阳辐射的综合影响，植物的响应不仅取决于大气蒸发需求，而且还取决于植物叶-木质部-根系内的水分输送。这些相互作用导致植物的动态响应，其中蒸腾滞后会影响植物提供的冷却。因此，详细了解这种动态是制定适当的缓解策略和数值模型的关键。在这项研究中，我们使用多种高分辨率非侵入式成像技术揭示了黄杨植物微气候的昼夜动态。尾流场是使用立体粒子图像测速法测量的，时空叶片温度历史是使用红外热成像获得的，此外，植物孔隙度是使用 X 射线断层扫描获得的。我们发现尾流速度统计数据与孔隙度的分布没有直接关系，而主要取决于产生剪切流的植物叶子的几何形状。剪切区和上游边界层剖面之间的相互作用被认为对尾流湍流动能分布具有主要影响。此外，叶面积密度分布对叶子内部的短波辐射热通量吸收有直接影响，其中 50% 的辐射被叶子的前 20% 吸收。这种局部辐射吸收导致局部叶片和空气温度升高。此外，叶片温度的昼夜变化与植物净蒸腾速率的比较使我们能够量化由气孔响应滞后引起的昼夜滞后。这种植物的一天被认为包括四个阶段的气候条件：无冷却、高冷却、平衡和衰减冷却阶段。