Does plant ecosystem thermoregulation occur? An extratropical assessment at different spatial and temporal scales

Abstract

Summary To what degree plant ecosystems thermoregulate their canopy temperature (Tc) is critical to assess ecosystems' metabolisms and resilience with climate change, but remains controversial, with opinions from no to moderate thermoregulation capability. With global datasets of Tc, air temperature (Ta), and other environmental and biotic variables from FLUXNET and satellites, we tested the ‘limited homeothermy’ hypothesis (indicated by Tc & Ta regression slope < 1 or Tc < Ta around midday) across global extratropics, including temporal and spatial dimensions. Across daily to weekly and monthly timescales, over 80% of sites/ecosystems have slopes ≥1 or Tc > Ta around midday, rejecting the above hypothesis. For those sites unsupporting the hypothesis, their Tc–Ta difference (ΔT) exhibits considerable seasonality that shows negative, partial correlations with leaf area index, implying a certain degree of thermoregulation capability. Spatially, site‐mean ΔT exhibits larger variations than the slope indicator, suggesting ΔT is a more sensitive indicator for detecting thermoregulatory differences across biomes. Furthermore, this large spatial‐wide ΔT variation (0–6°C) is primarily explained by environmental variables (38%) and secondarily by biotic factors (15%). These results demonstrate diverse thermoregulation patterns across global extratropics, with most ecosystems negating the ‘limited homeothermy’ hypothesis, but their thermoregulation still occurs, implying that slope < 1 or Tc < Ta are not necessary conditions for plant thermoregulation.

A data‐intensive documentation of plant ecosystem thermoregulation across spatial and temporal scales

“…Despite the strong role of the environment in determining T c , Guo et al (2023) also present evidence of significant thermoregulation by plants. First, they simulated the thermodynamics at three sites using the Breathing Earth System Simulator (BESS) and found that T c was consistently lower than soil temperatures, such that plants still exhibited thermoregulation even when T c > T air , as the canopy was cooler than objects without thermoregulation.…”

“…However, the results of Guo et al . (2023) suggest that this may vary across ecosystem types, as forest ecosystems had higher thermoregulation capacity than savanna, shrublands, grasslands, and croplands in their dataset. Whether this translates to a response of forests warming at a slower rate than other ecosystem types in the context of climate change is an important question.…”

“…S1 in this issue of New Phytologist by Guo et al . (2023; pp. 1004–1018)) and the relevance of leaf traits (b–d).…”

“…1; homeothermy). A new paper published in this issue of New Phytologist by Guo et al (2023;pp. 1004-1018 brings a large and spatially extensive dataset to bear on this issue, providing novel insight regarding the degree of thermoregulation across a wide range of ecosystem types.…”

“…Plant phenotypes are shaped by evolutionary history and can affect organismal thermal biology in a way that does not require sentience or intentionality. Guo et al (2023) bring a wealth of data to bear on the issue of thermoregulation of the temperature of plant canopies, utilizing 146 sites and 965 site-years from a global eddy-covariance database (Baldocchi, 2003;Pastorello et al, 2020) combined with satellite remote sensing of canopy temperatures (MODIS). They find a diversity of slopes between canopy temperature (T c ) and T air , ranging from 0.7 ('limited homeothermy') to 1.3 ('megathermy'; Fig.…”