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

Abstract

To what degree plant ecosystems thermoregulate their canopy temperature (T-c) 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 T-c, air temperature (T-a), and other environmental and biotic variables from FLUXNET and satellites, we tested the 'limited homeothermy' hypothesis (indicated by T-c & T-a regression slope < 1 or T-c < T-a 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 T-c > T-a around midday, rejecting the above hypothesis. For those sites unsupporting the hypothesis, their T-c-T-a difference (Delta T) exhibits considerable seasonality that shows negative, partial correlations with leaf area index, implying a certain degree of thermoregulation capability. Spatially, site-mean Delta T exhibits larger variations than the slope indicator, suggesting Delta T is a more sensitive indicator for detecting thermoregulatory differences across biomes. Furthermore, this large spatial-wide Delta T variation (0-6 degrees 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 T-c < T-a are not necessary conditions for plant thermoregulation.