Dissolved gas dynamics in wetland soils: Root-mediated gas transfer kinetics determined via push-pull tracer tests

Abstract

Gas transfer processes are fundamental to the biogeochemical and water quality functions of wetlands, yet there is limited knowledge of the rates and pathways of soil‐atmosphere exchange for gases other than oxygen and methane (CH4). In this study, we use a novel push‐pull technique with sulfur hexafluoride (SF6) and helium (He) as dissolved gas tracers to quantify the kinetics of root‐mediated gas transfer, which is a critical efflux pathway for gases from wetland soils. This tracer approach disentangles the effects of physical transport from simultaneous reaction in saturated, vegetated wetland soils. We measured significant seasonal variation in first‐order gas exchange rate constants, with smaller spatial variations between different soil depths and vegetation zones in a New Jersey tidal marsh. Gas transfer rates for most biogeochemical trace gases are expected to be bracketed by the rate constants for SF6 and He, which ranged from ∼10−2 to 2 × 10−1 h−1 at our site. A modified Damköhler number analysis is used to evaluate the balance between biochemical reaction and root‐driven gas exchange in governing the fate of environmental trace gases in rooted, anaerobic soils. This approach confirmed the importance of plant gas transport for CH4, and showed that root‐driven transport may affect nitrous oxide (N2O) balances in settings where N2O reduction rates are slow.

Control Effects of Chelonus munakatae Against Chilo suppressalis and Impact on Greenhouse Gas Emissions From Paddy Fields

“…The PCA results also imply that GHGs were highly positively correlated with the growth of rice roots (Figure 3). This conclusion is supported by numerous studies, which suggests that plant-mediated transport is a major pathway for gas efflux in submerged soil (Hosono and Nouchi, 1997;Groot et al, 2005;Reid et al, 2015) and more than 80% of both N 2 O and CH 4 is emitted through rice plants (Yu et al, 1997;Watanabe et al, 1999;Yan et al, 2000). Similarly, the relatively higher fluxes (Figure 1) and seasonal accumulative emissions (Table 2) of N 2 O and CH 4 as well as the significantly higher total seasonal GWP ( Table 2) under CS+CM than under CS may also be owing to the lower damage on rice plants under CS+CM ( Supplementary Table S3 and Table 1) as mentioned above.…”

Soil carbon dioxide venting through rice roots

“…In general, the former dominates (Yao & Conrad, ), and = 1 is typical (Kirk, ). A large proportion of the CH 4 flux will be oxidized to CO 2 by methanotrophic bacteria in the rhizosphere and oxic floodwater–soil interface; up to 95% of the root‐mediated CH 4 flux is oxidized to CO 2 (Arah & Kirk, ; Cho, Schroth, & Zeyer, ; Hernández, Dumont, Yuan, & Conrad, ; Reid, Pal, & Jaffe, ; van Bodegom, Stams, Mollema, Boeje, & Leffelaar, ). The net root CO 2 flux will be correspondingly greater.…”

HIMMELI v1.0: HelsinkI Model of MEthane buiLd-up and emIssion for peatlands

“…The area of root surface permeable to gases was the most important factor controlling the CH 4 flux in Juncus effusus, another aerenchymatous species, and this permeable surface is concentrated in fine roots and the tips of coarser roots (Hennenberg et al, 2012). According to Reid et al (2015), the rate for root-mediated gas transport in P. australis and Spartina patens increased during the growing season, indicating increase of permeable root surface area or aerenchyma along the summer. Thus, the growth of the plants seems to affect their gas transport capacity.…”