TIME-INTEGRATED COLLECTION OF CO2FOR14C ANALYSIS FROM SOILS

Shawn Pedron,R G Jespersen,X Xu,E S Klein,C I Czimczik,J C Walker,J M Welker,J C Ferguson

doi:10.1017/rdc.2021.42

Abstract

ABSTRACTWe developed a passive sampler for time-integrated collection and radiocarbon (14C) analysis of soil respiration, a major flux in the global C cycle. It consists of a permanent access well that controls the CO2uptake rate and an exchangeable molecular sieve CO2trap. We tested how access well dimensions and environmental conditions affect collected CO2, and optimized cleaning procedures to minimize14CO2memory. We also deployed two generations of the sampler in Arctic tundra for up to two years, collecting CO2over periods of 3 days–2 months, while monitoring soil temperature, volumetric water content, and CO2concentration. The sampler collects CO2at a rate proportional to the length of a silicone tubing inlet (7–26 µg CO2-C day-1·m Si-1). With constant sampler dimensions in the field, CO2recovery is best explained by soil temperature. We retrieved 0.1–5.3 mg C from the 1st and 0.6–13 mg C from the 2nd generation samplers, equivalent to uptake rates of 2–215 (n=17) and 10–247 µg CO2-C day-1(n=20), respectively. The method blank is 8 ± 6 µg C (mean ± sd,n=8), with a radiocarbon content (fraction modern) ranging from 0.5875–0.6013 (n=2). The sampler enables more continuous investigations of soil C emission sources and is suitable for Arctic environments.

Highlights

Soil respiration, the emission of carbon dioxide CO2 from soils, is a major flux in the global carbon (C) cycle, and its radiocarbon content (here reported as fraction modern carbon (F) (Trumbore et al 2016)) allows insights to the cycling of C in terrestrial ecosystems (Trumbore 2009)
We developed a passive sampler for time-integrated collection and radiocarbon (14C) analysis of soil respiration, a major flux in the global C cycle
The F of soil respiration is a measure of the amount of time that has passed since the constituent C atoms were last in the atmosphere, integrating the transit through various reservoirs, including plant and microbial biomass, soil organic matter, and carbonates (Sierra et al 2017)

Summary

Introduction

The emission of carbon dioxide CO2 from soils, is a major flux in the global carbon (C) cycle, and its radiocarbon content (here reported as fraction modern carbon (F) (Trumbore et al 2016)) allows insights to the cycling of C in terrestrial ecosystems (Trumbore 2009). Along with its δ13C signature (Hicks Pries et al 2013), soil FCO2 can be used to partition soil C emissions into contributions from the rhizosphere (respiration of roots and associated microorganisms) relative to those from microorganisms that decompose soil organic matter to reveal how plant and microbial activity and microbial C sources are influenced by changes in environmental conditions (Trumbore 2006, 2000; Hicks Pries et al 2013). Many investigations of soil FCO2 collect net soil respiration from chambers or soil pore space CO2 from gas wells

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Conclusion