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Abstract The creation and/or restoration of wetlands is an important strategy for controlling the release of reactive nitrogen (N) via denitrification, but there can be tradeoffs between enhanced denitrification and the production of nitrous oxide (N2O), a potent greenhouse gas. A knowledge gap in current understanding of belowground wetland N dynamics is the role of gas transfer through the root aerenchyma system of wetland plants as a shortcut emission pathway for N2O in denitrifying wetland soils. This investigation evaluates the significance of mass transfer into gas‐filled root aerenchyma for the N2O budget in wetland mesocosms planted withSagittaria latifoliaWilld. andSchoenoplectus acutus(Muhl. ex Bigelow) Á. Löve & D. Löve. Dissolved gas tracer push–pull tests with N2O and the nonreactive gas tracers helium, sulfur hexafluoride, and ethane were used to estimate first‐order rate constants for gas transfer into roots and microbial N2O reduction and thereby disentangle the effects of root‐mediated gas transport from microbial metabolism on N2O balances in saturated soils. Root‐mediated gas transport was estimated to account for up to 37% of overall N2O removal from the wetland soils. Rates of microbial N2O reduction varied widely based on the organic matter content of the soil media and served as a key control on the fraction of N2O that transferred into roots. This research identifies transport through root aerenchyma as a potential shortcut pathway for N2O emission from wetland soils and sediments and indicates that this process should be considered in both measurements and mechanistic modeling of belowground wetland N dynamics.
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Response of Root Respiration to Warming and Nitrogen Addition Depends on Tree Species
ABSTRACT Roots contribute a large fraction of CO2efflux from soils, yet the extent to which global change factors affect root‐derived fluxes is poorly understood. We investigated how red maple (Acer rubrum) and red oak (Quercus rubra) root biomass and respiration respond to long‐term (15 years) soil warming, nitrogen addition, or their combination in a temperate forest. We found that ecosystem root respiration was decreased by 40% under both single‐factor treatments (nitrogen addition or warming) but not under their combination (heated × nitrogen). This response was driven by the reduction of mass‐specific root respiration under warming and a reduction in maple root biomass in both single‐factor treatments. Mass‐specific root respiration rates for both species acclimated to soil warming, resulting in a 43% reduction, but were not affected by N addition or the combined heated × N treatment. Notably, the addition of nitrogen to warmed soils alleviated thermal acclimation and returned mass‐specific respiration rates to control levels. Oak roots contributed disproportionately to ecosystem root respiration despite the decrease in respiration rates as their biomass was maintained or enhanced under warming and nitrogen addition. In contrast, maple root respiration rates were consistently higher than oak, and this difference became critical in the heated × nitrogen treatment, where maple root biomass increased, contributing significantly more CO2relative to single‐factor treatments. Our findings highlight the importance of accounting for the root component of respiration when assessing soil carbon loss in response to global change and demonstrate that combining warming and N addition produces effects that cannot be predicted by studying these factors in isolation.
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- Award ID(s):
- 1832210
- PAR ID:
- 10559826
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 30
- Issue:
- 10
- ISSN:
- 1354-1013
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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