Soil CO2 Dynamics in a Tree Island Soil of the Pantanal: The Role of Soil Water Potential

Abstract

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 CO2 research has been conducted in this region. We evaluated soil CO2 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 CO2 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 CO2 efflux and related environmental parameters. Soil CO2 efflux during the study averaged 3.53 µmol CO2 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 CO2 concentrations, with high CO2 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 CO2 efflux from the tree island soil, with soil CO2 dynamics differing by wetting mechanism. During the wet-up period, direct precipitation infiltrates soil from above and results in pulses of CO2 efflux from soil. The annual flood arrives later, and saturates soil from below. While CO2 concentrations in soil grew very high under both wetting mechanisms, the change in soil CO2 efflux was only significant when soils were wet from above.

Loss of deep roots limits biogenic agents of soil development that are only partially restored by decades of forest regeneration

“…Though a weak acid, carbonic acid can be a potent contributor to soil acidification (Reuss and Johnson, 1986;Amundson and Davidson, 1990;Richter and Markewitz, 1995;Richter and Markewitz, 2001) as soil CO 2 concentrations can regularly exceed 5% in deep soil horizons (Richter and Markewitz, 2001;Johnson et al, 2013;Hasenmueller et al, 2015;Lathuillière et al, 2017), driving this reaction forward. Organic acids are also generated by microbes and roots and additionally contribute to soil acidification, as demonstrated by the commonly occurring OA oxalic acid: -+ 2-+ 2 4 2 2 4 2 4…”

Physiological responses to extreme hydrological events in the Pantanal wetland: heterogeneity of a plant community containing super‐dominant species

“…) and soil respiration (Johnson et al. ). Soil at the tree island site was classified as Haplic Planosol (Johnson et al.…”

Albedo do Solo abaixo do Dossel em Área de Vochysia divergens Pohl no Norte do Pantanal

“…A precipitação pluviométrica oscila entre 800 e 1500 mm ano -1 (Johnson et al, 2013;Fantim-Cruz et al, 2010) ocorrendo principalmente entre novembro a abril, meses úmidos. As precipitações de alta intensidade provocam inundações em toda a planície de inundação de baixo-relevo, começando entre novembro a dezembro ou na parte norte do Pantanal.…”

“…3). Provavelmente devido a saturação de água no solo e consequentemente a coloração escura da água, devido ao alto teor de matéria orgânica no solo, presente na área de estudo (Johnson et al, 2013). As maiores médias ocorreram em setembro nos transectos A, C e E, respectivamente, provavelmente porque o solo está mais seco neste final do período de estiagem.…”