Carbon flux estimates are sensitive to data source: a comparison of field and lab temperature sensitivity data

Abstract

A large literature exists on mechanisms driving soil production of the greenhouse gases CO2 and CH4. Although it is common knowledge that measurements obtained through field studies vs. laboratory incubations can diverge because of the vastly different conditions of these environments, few studies have systematically examined these patterns. These data are used to parametrize and benchmark ecosystem- to global-scale models, which are then susceptible to the biases of the source data. Here, we examine how greenhouse gas measurements may be influenced by whether the measurement/incubation was conducted in the field vs. laboratory, focusing on CO2 and CH4 measurements. We use Q10 of greenhouse gas flux (temperature sensitivity) for our analyses because this metric is commonly used in biological and Earth system sciences and is an important parameter in many modeling frameworks. We predicted that laboratory measurements would be less variable, but also less representative of true field conditions. However, there was greater variability in the Q10 values calculated from lab-based measurements of CO2 fluxes, because lab experiments explore extremes rarely seen in situ, and reflect the physical and chemical disturbances occurring during sampling, transport, and incubation. Overall, respiration Q10 values were significantly greater in laboratory incubations (mean = 4.19) than field measurements (mean = 3.05), with strong influences of incubation temperature and climate region/biome. However, this was in part because field measurements typically represent total respiration (Rs), whereas lab incubations typically represent heterotrophic respiration (Rh), making direct comparisons difficult to interpret. Focusing only on Rh-derived Q10, these values showed almost identical distributions across laboratory (n = 1110) and field (n = 581) experiments, providing strong support for using the former as an experimental proxy for the latter, although we caution that geographic biases in the extant data make this conclusion tentative. Due to a smaller sample size of CH4 Q10 data, we were unable to perform a comparable robust analysis, but we expect similar interactions with soil temperature, moisture, and environmental/climatic variables. Our results here suggest the need for more concerted efforts to document and standardize these data, including sample and site metadata.

Twenty Years of Progress, Challenges, and Opportunities in Measuring and Understanding Soil Respiration

“…Results can be affected by experimental protocols (X. Chen et al., 2010) as well as experiment length (Birge et al., 2015; Hamdi et al., 2013). Extrapolating such results to in situ conditions, or using them to parameterize models, must be done with caution (J. Chen et al., 2023; Patel et al., 2022).…”

“…Extrapolating such results to in situ conditions, or using them to parameterize models, must be done with caution (J. Patel et al, 2022).…”

Reservoir Routing and Its Application to Atmospheric Carbon Dioxide Balance

“…The remaining points are obtained from the so-called 𝑄𝑄 10 model [55], as in Koutsoyiannis et al [30 (Appendix A.1)]. This is based on the equation:…”

Radiocarbon analysis of soil microbial biomass via direct chloroform extraction

“…We found that both incubation and chloroform extraction methods of estimating microbial biomass C produced similar ∆ 14 C results in the upper 50 cm soil increment, indicating that for these surface soils, either method could be used to assess microbially used C. In contrast, the ∆ 14 C values for soil collected from below 50 cm from the two methods diverge. It is possible that the soil sampling process and sample handling prior to incubation released fresh, labile C that otherwise would not have been accessible for decomposition (Salomé et al 2010, Herbst et al 2016, Schädel et al 2020, Patel et al 2022. Alternatively, the 14 C depleted biomass values in the deeper soils may reflect non-living cell material that was liberated by the chloroform biomass extraction.…”

“…Given the importance of microbial SOC cycling, many studies use laboratory soil incubations to measure the rate of heterotrophic respiration and the ∆ 14 C of respired CO2 to assess C turnover utilization by microbes. While incubations provide an integrated assessment of microbial respiration and C turnover, soil sampling and preparation prior to incubation can result in artifacts due to the disruption of soil structure, roots, and microbial communities (Salomé et al 2010, Herbst et al 2016, Schädel et al 2020, Patel et al 2022. Comparisons between field-based and laboratory incubation studies show differences in gas flux rates (Williams et al 1998, Patel et al 2022, Risk et al 2008) and younger respired C in the field (Phillips et al 2013), suggesting that additional methods to assess microbial processes would be valuable.…”