Soil CO(2) Dynamics in a Tree Island Soil of the Pantanal: The Role of Soil Water Potential

The Pantanal is a biodiversity hotspot comprised of a mosaic of landforms that differ in vegetative assemblages and flooding dynamics. Tree islands provide refuge for terrestrial fauna during the flooding period and are particularly important to the regional ecosystem structure. Little soil CO(2) research has been conducted in this region. We evaluated soil CO(2) dynamics in relation to primary controlling environmental parameters (soil temperature and soil water). Soil respiration was computed using the gradient method using in situ infrared gas analyzers to directly measure CO(2) concentration within the soil profile. Due to the cost of the sensors and associated equipment, this study was unreplicated. Rather, we focus on the temporal relationships between soil CO(2) efflux and related environmental parameters. Soil CO(2) efflux during the study averaged 3.53 µmol CO(2) m(−2) s(−1), and was equivalent to an annual soil respiration of 1220 g C m(−2) y(−1). This efflux value, integrated over a year, is comparable to soil C stocks for 0–20 cm. Soil water potential was the measured parameter most strongly associated with soil CO(2) concentrations, with high CO(2) values observed only once soil water potential at the 10 cm depth approached zero. This relationship was exhibited across a spectrum of timescales and was found to be significant at a daily timescale across all seasons using conditional nonparametric spectral Granger causality analysis. Hydrology plays a significant role in controlling CO(2) efflux from the tree island soil, with soil CO(2) dynamics differing by wetting mechanism. During the wet-up period, direct precipitation infiltrates soil from above and results in pulses of CO(2) efflux from soil. The annual flood arrives later, and saturates soil from below. While CO(2) concentrations in soil grew very high under both wetting mechanisms, the change in soil CO(2) efflux was only significant when soils were wet from above.