PNNL

Abstract

1. Accurately measuring the soil-to-atmosphere CO2 flux (soil respiration, RS) is important to understanding terrestrial carbon balance and to forecasting climate change. Such measurements are frequently made using measurement collars permanently inserted into the soil surface. However, differences in collar properties, measurement time and duration, and measurement frequency may lead to biases in the estimation of annual RS bias. 2. Using a newly updated global RS database (SRDB-V5), we investigated the annual RS bias associated with five methodological factors: collar height, collar coverage area, collar insertion depth, measurement time, and measurement frequency. 3. We found that annual RS was negatively correlated with collar height and collar coverage area, consistent with the idea that uniform head-space mixing is difficult to achieve in larger volume chambers; however, these effects were quantitatively small (bias of ~6% to 9% of mean RS). We found no correlation of collar insertion depth, measurement time, or measurement frequency with annual RS. 4. These findings suggest that variation in RS methodology generally introduces minimal bias except in cases when soil chamber height and/or area are especially high–i.e., chamber volume is large. Therefore, compilations of minimally adjusted annual RS measurements provide an important and reliable resource for synthesis studies, global annual RS modeling, as well as investigation of how soil carbon responds to climate change.