The ‘Gas-Snake’: Design and validation of a versatile membrane-based gas flux measurement system in a grassland soil respiration study

Soil respiration (SR) is a major flux component of the terrestrial carbon (C) cycle, and of particular importance for model predictions on potential terrestrial climate change feedbacks. Globally grasslands contain large amounts of soil organic carbon and highly active roots, but quantifying their SR and understanding its responses is complicated by inadequate methodology. So far, direct measurement of soil CO2 efflux from grassland has only been achieved after removal of the above-ground vegetation, with badly constrained effects on SR via changes in soil microclimate and altered belowground carbon allocation. We developed the ‘Gas-Snake’, a novel flexible membrane-based soil surface flux system, using micro-polyvinylidene difluoride flat membrane (PVDF) in connection with a chamber based Li-Cor 8100 CO2 analyser unit and a flushing system. The ‘Gas-Snake’ is pushed onto the soil surface without the need for clipping or burial. After flushing with ambient air, the tube air equilibrates with soil air through the membrane underside allowing direct soil efflux calculations. We performed both laboratory and field tests including validation against established chamber techniques. The membrane-based ‘Gas-Snake’ system is inexpensive and provides distinct methodological advances, allowing (i) rapid diffusion of CO2 into a closed loop analyser system with short flux calculation periods, and (ii) non-intrusive in situ measurements of soil respiration within dense vegetation. Further considerations of potential for other applications are discussed.