Widespread inhibition of daytime ecosystem respiration

Abstract

The global land surface absorbs about a third of anthropogenic emissions each year, due to the difference between two key processes: ecosystem photosynthesis and respiration. Despite the importance of these two processes, it is not possible to measure either at the ecosystem scale during daytime. Eddy-covariance measurements are widely used as the closest ‘quasi-direct’ ecosystem-scale observation from which to estimate ecosystem photosynthesis and respiration. Recent research, however, suggests that current estimates may be biased by up to 25%, due to a previously unaccounted-for process: the inhibition of leaf respiration in the light. Yet the extent of inhibition remains debated, and implications for estimates of ecosystem-scale respiration and photosynthesis remain unquantified. Here, we quantify an apparent inhibition of daytime ecosystem respiration across the global FLUXNET eddy-covariance network, and identify a pervasive influence that varies by season and ecosystem type. We develop partitioning methods that can detect an apparent ecosystem-scale inhibition of daytime respiration and find that diurnal patterns of ecosystem respiration might be markedly different than previously thought. The results call for the reevaluation of global terrestrial carbon cycle models, and also suggest that current global estimates of photosynthesis and respiration may be biased, some on the order of magnitude of anthropogenic fossil fuel emissions.

Seasonal Controls of CO2 and CH4 Dynamics in a Temporarily Flooded Subtropical Wetland

“…It is likely that in using this gap filling and partitioning methods, we overestimated the temperature sensitivity of gap filled NEE, and that we also overestimated or underestimated R eco due to the inhibition of respiration during light conditions, particularly at daily scales. However, annual estimates, as reported in this study, are less affected by this phenomena as recently reported (Desai et al, ; Keenan et al, ).…”

Scaling carbon fluxes from eddy covariance sites to globe: synthesis and evaluation of the FLUXCOM approach

“…At FLUXNET sites night-time CO 2 advection and storage could cause underestimation of night-time CO 2 fluxes (Aubinet et al, 2012;McHugh et al, 2017;van Gorsel et al, 2009) and thus underestimate GPP using the night-time NEE flux partitioning method. On the contrary, it has been suggested that FLUXNET GPP estimated from the night-time partitioning method (Reichstein et al, 2005) is overestimated as it ignores the effects of light inhibition of leaf respiration (Keenan et al, 2019;Wehr et al, 2016) by on average 7 % across FLUXNET sites (Keenan et al, 2019). But it should be noted that this value may not be globally representative due to sizable variations between ecosystems and leaf area.…”

Hot moments in ecosystem fluxes: High GPP anomalies exert outsized influence on the carbon cycle and are differentially driven by moisture availability across biomes

“…Our results using both partitioning approaches were quantitatively similar, and we observed a strong relationship between annual impact calculated with either daytime-partitioned or nighttime-partitioned data (figure S1, p < 0.0001, r 2 = 0.61). Thus, we focused on daytime-partitioned data since (1) nighttime-partitioned data can have negative values for GPP which slightly skew our calculations of impact, and (2) the daytime approach has recently been shown to be less prone to biases in flux partitioning related to light inhibition of respiration during the day (Keenan et al 2019), which becomes especially important since our analysis was only conducted on daytime data. Additionally, our results were the same after omitting any medium or poor quality gap-filled data (a quality flag of >1 in the FLUXNET2015 dataset, figure S2, p < 0.0001, r 2 = 0.87), indicating that FLUXNET gap-filling algorithms were unlikely to have caused hot moments in GPP.…”