The Apparent Respiratory Quotient of Soils and Tree Stems and the Processes That Control It

Abstract

New measurement methods can improve the understating and prediction of ecosystem processes. An emerging tool in biogeochemical studies is the coupled measurement of CO 2 and O 2 fluxes. In respiration the ratio CO 2 production/O 2 consumption is termed the "respiratory quotient" (RQ). The inverse term "oxidative ratio" (OR, 1/RQ) is also used, especially when describing ecosystem processes that include photosynthesis with O 2 production (where the fluxes direction is opposite to respiration). Both ratios depend primarily on the stoichiometry, of the respiratory substrate or the net synthesized biomass. The stoichiometry of an organic molecule determines the mean oxidation state (C ox ) of the C atoms in the molecule (LaRowe & Van Cappellen, 2011;Masiello et al., 2008). The more oxidized (higher C ox ) the molecule, the fewer moles of O 2 are consumed per mole of CO 2 released during complete oxidation and the RQ is higher (Table 1). For this reason RQ is often used to infer which

Atmospheric O2 and CO2 measurements at a single height provide weak constraint on surface carbon exchange

“…for both years would have remained consistent. Previous studies suggest that ER r is generally higher than ER a , even under different atmospheric conditions (Angert et al, 2015;Fischer et al, 2015;Hilman et al, 2022). The effect of a warmer and dryer environment on the ER atmos signal will be further quantified in Sect.…”

“…To advance our understanding of the ER signals over forest canopies, it is crucial to incorporate ER signals that can respond to varying soil and atmospheric conditions. For instance, the ER r of the soil respiration depends on air temperature and soil moisture (Hilman et al, 2022;Angert et al, 2015), while the ER a is primarily influenced by nitrogen content and light on leaf level (Bloom, 2015;Fischer et al, 2015). Additionally, in our current implementation, we did not include the ER for stem respiration (ER stem ) (Hilman and Angert, 2016) due to the absence of stem respiration in the CLASS model.…”

“…Rising atmospheric carbon dioxide (CO 2 ) levels, resulting from fossil fuel combustion and land use change emissions and uptake by the terrestrial biosphere and oceans require a comprehensive assessment of the carbon exchange at local and global scales (Friedlingstein et al, 2022). Atmospheric oxygen (O 2 ) serves as a valuable tracer in enhancing our understanding of carbon exchange, due to the close linkage between O 2 and carbon dioxide (CO 2 ) in carbon cycle processes such as fossil fuel combustion, photosynthesis and respiration (Manning and Keeling, 2006;Worrall et al, 2013;Keeling and Manning, 2014;Bloom, 2015;Hilman et al, 2022). The Exchange Ratio (ER = -O 2 /CO 2 ), denoted as the number of moles of O 2 exchanged per mole of CO 2 represents the specific link between O 2 and CO 2 for different processes (Keeling et al, 1998).…”

“…However, the ER of terrestrial biosphere exchange is not uniform at smaller scales; it varies between ecosystems and over time (Angert et al, 2015;Bloom, 2015;Battle et al, 2019;Hilman et al, 2022). Measuring the ERs of ecosystems and the underlying gross processes facilitates the partitioning of Net Ecosystem Exchange (NEE) into Gross Primary Production (GPP) and Total Ecosystem Respiration (TER) (Ishidoya et al, 2015;Faassen et al, 2023) which is still challenging (Reichstein et al, 2005).…”

Monitoring and modelling European carbon fluxes using atmospheric observations

“…Oxygen Similar to different fuels, also different plant components are composed of different ratios of carbon to other molecules, resulting in different oxidative ratios for different parts of the plant (Hilman et al, 2022;Jürgensen et al, 2021;Worrall et al, 2013). These ratios could be built in the different carbon pools of e.g.…”