Does plant ecosystem thermoregulation occur?

To what extent plants thermoregulate their canopy temperature (Tc) in response to environmental variability is a fundamental question in ecology, and influences accurate projections of plants' metabolic response and resilience to climate change. However, debate remains, with opinions ranging from no to moderate plant thermoregulation capacities. Traditionally, it has been hypothesized that if plant thermoregulation occurs (i.e. ‘limited homeothermy’ hypothesis holds): 1) Tc will change more slowly than Ta over time, leading the Tcvs. Ta regression slope < 1; 2) Tc is cooler than Ta when Ta exceeds some threshold, typically during high net radiation conditions (e.g. at midday). Here, with global datasets of Tc, air temperature (Ta), and other environmental and biotic variables from FLUXNET and satellites, we tested the ‘limited homeothermy’ hypothesis across global extratropics, including temporal and spatial dimensions. Our results demonstrate that across daily to monthly timescales, over 80% of sites/ecosystems have Tcvs. Ta regression slopes≥1 or Tc>Ta around midday, which rejects the ‘limited homeothermy’ hypothesis. For those sites unsupporting the hypothesis, their Tc-Ta difference (ΔT) still exhibits considerable seasonality that is negatively, partially correlated with their canopy structure seasonality (as indicated by leaf area index), implying a certain degree of thermoregulation capability. Across global sites, both site-mean ΔT and slope indicator exhibit considerable spatial variability, with ΔT having greater variability than the slope indicator. Furthermore, this large spatial ΔT variation (0-6°C) can be mainly explained by environmental variables (38%) and, to a lesser extent, by biological factors (15%). Our results suggested that plant thermoregulation patterns are diverse across global extratropics, with most ecosystems rejecting the ‘limited homeothermy’ hypothesis, but their thermoregulation still occurs, implying that slope