Canopy temperature dynamics are closely aligned with ecosystem water availability across a water- to energy-limited gradient

Authors: JAVADIAN, M. - Northern Arizona University; Scott, Russell - Russ; WOODGATE, W. - University Of Queensland; RICHARDSON, A.D. - Northern Arizona University; DANNENBERG, M.P. - University Of Iowa; SMITH, W.K. - University Of Arizona

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/2023
Publication Date: 8/28/2024
Citation: Javadian, M., Scott, R.L., Woodgate, W., Richardson, A., Dannenberg, M., Smith, W. 2024. Canopy temperature dynamics are closely aligned with ecosystem water availability across a water- to energy-limited gradient. Agricultural and Forest Meteorology. 357. Article 110206. https://doi.org/10.1016/j.agrformet.2024.110206.
DOI: https://doi.org/10.1016/j.agrformet.2024.110206

Interpretive Summary: Canopy temperature has long been recognized as important for plant growth and productivity. The canopy temperature is an indicator of plant water status and how the land absorbs heat from the sun, which makes it significant for understanding ecosystems and predicting responses to environmental change. Still, a better understanding of the relationship between the canopy temperature and water availability is needed to enable accurate monitoring of photosynthesis and plant water use. Here, we used high resolution thermal infrared cameras deployed at a predominately dry shrubland site, a seasonally dry evergreen needleleaf forest, and a predominantly wet deciduous forest – to determine seasonality of canopy temperature and its relationship with ecosystem photosynthesis and environmental drivers. We found that canopy temperature was warmer than air temperature during most of the growing season at all sites. Also, canopy temperatures grew even warmer than air temperatures from the dry shrubland to the deciduous forest. We also introduced a predictor for canopy temperature as a function of solar radiation and soil water. Our findings provide insights into canopy temperature dynamics and ecosystem water availability and has implications for ecosystem management in a changing climate.

Technical Abstract: Canopy temperature (Tc) plays an important role in regulating the rates of mass and energy fluxes at the leaf surface. A better understanding of the relationship between Tc and water availability is needed to enable accurate monitoring of ecosystem functioning in a changing climate. Here, we used high spatiotemporal resolution thermal infrared cameras deployed at three eddy covariance flux tower sites along a water- to energy-limited gradient – including a predominately water-limited grassland/shrubland site, a seasonally water-limited evergreen needleleaf forest, and a predominantly energy-limited deciduous broadleaf forest – to determine Tc seasonality and its relationship with gross primary productivity (GPP) and environmental drivers. We found midday Tc was generally warmer than air temperature (Tair) during the growing season (Tc:Tair slope: 1.14-1.27) for all sites. Water-limited sites exhibited higher Tc deviations from Tair (2.30 ± 1.2°C) compared to the energy-limited site (1.29 ± 0.8°C) partly due to their increased sensible and reduced latent heat fluxes during water-limited periods. We further found that the Tc:Tair slope increased with site aridity for 1.14 for the grassland, 1.15 for the evergreen forest, and 1.27 for the broadleaf forest. Peak GPP occurred when Tc was higher than Ta across all sites, with peak GPP at the grassland site occurring at +1.1°C (Tc-Tair) and peak GPP at the broadleaf evergreen site occurring at +2.2°C (Tc-Tair). Tc-Tair dynamics were mostly associated with soil water content at water-limited sites where canopies undergo a substantial cooling during the transition from dormancy to the peak GPP, while net radiation played a crucial role at the energy-limited site where the canopy heats up compared to Tair over the same phenological transition. Our findings provide novel insights into Tc-ecosystem water availability links, highlighting the drivers of Tc-Tair across diverse ecosystems in various phenological stages, which has implications for ecosystem management in a changing climate.