Temperature response of denitrification rate and greenhouse gas production in agricultural river marginal wetland soils

Abstract

Soils are predicted to exhibit significant feedback to global warming via the temperature response of greenhouse gas (GHG) production. However, the temperature response of hydromorphic wetland soils is complicated by confounding factors such as oxygen (O2 ), nitrate (NO3-) and soil carbon (C). We examined the effect of a temperature gradient (2-25 °C) on denitrification rates and net nitrous oxide (N2 O), methane (CH4 ) production and heterotrophic respiration in mineral (Eutric cambisol and Fluvisol) and organic (Histosol) soil types in a river marginal landscape of the Tamar catchment, Devon, UK, under non-flooded and flooded with enriched NO3- conditions. It was hypothesized that the temperature response is dependent on interactions with NO3--enriched flooding, and the physicochemical conditions of these soil types. Denitrification rate (mean, 746 ± 97.3 μg m(-2) h(-1) ), net N2 O production (mean, 180 ± 26.6 μg m(-2) h(-1) ) and net CH4 production (mean, 1065 ± 183 μg m(-2) h(-1) ) were highest in the organic Histosol, with higher organic matter, ammonium and moisture, and lower NO3- concentrations. Heterotrophic respiration (mean, 127 ± 4.6 mg m(-2) h(-1) ) was not significantly different between soil types and dominated total GHG (CO2 eq) production in all soil types. Generally, the temperature responses of denitrification rate and net N2 O production were exponential, whilst net CH4 production was unresponsive, possibly due to substrate limitation, and heterotrophic respiration was exponential but limited in summer at higher temperatures. Flooding with NO3- increased denitrification rate, net N2 O production and heterotrophic respiration, but a reduction in net CH4 production suggests inhibition of methanogenesis by NO3- or N2 O produced from denitrification. Implications for management and policy are that warming and flood events may promote microbial interactions in soil between distinct microbial communities and increase denitrification of excess NO3- with N2 O production contributing to no more than 50% of increases in total GHG production.

Land Use and Climate Variability Amplify Carbon, Nutrient, and Contaminant Pulses: A Review with Management Implications

“…Warming may increase N 2 O emissions in agricultural riparian zones and wetlands (Maag et al ., ; Munoz‐Leoz et al ., ; Soosaar et al ., ). In the United Kingdom (UK), the effects of temperature on N 2 O emissions have been studied in flooded and nonflooded agricultural floodplain wetlands, and this work has shown that flooding and warming can synergistically increase N 2 O emissions (Bonnett et al ., ). Increased flooding frequency led to higher emissions of N 2 O in an agricultural riparian zone in Indiana (Jacinthe et al ., ).…”

“…() studied continually inundated agricultural wetlands in Ohio and found that experimentally pulsed flood flows significantly decreased CH 4 emissions. There may be other abiotic and biotic factors that are drivers of CH 4 emissions (Sovik et al ., ; Mander et al ., ; Samaritani et al ., ; Sha et al ., ) including inhibition by nitrate and N 2 O during floods (Bonnett et al ., ). Thus, the response of CH 4 to flooding and temperature can also be ecosystem specific (Le Mer and Roger, ).…”

“…CH 4 emissions can also increase in riparian zones/floodplains/wetlands and streams/rivers with warming, but the response is not as strong because CH 4 consumption also increases (Verma et al ., ; Harrison et al ., ; Bonnett et al . ; Sha et al ., ; Yang et al ., ). Warming can also increase CO 2 emissions (Davidson et al ., ; Verma et al ., ; Mander et al ., ; Munoz‐Leoz et al ., ).…”

“…References B (Temperature): Warming can increase N 2 O emission riparian zones/floodplains/wetlands and streams/rivers when conditions necessary for denitrification are present (Maag et al ., ; McMahon and Dennehy, ; Laursen and Seitzinger, ; Hernandez and Mitsch, ; DeSimone et al ., ; Bonnett et al . ; Munoz‐Leoz et al ., ; Baulch et al ., ). CH 4 emissions can also increase in riparian zones/floodplains/wetlands and streams/rivers with warming, but the response is not as strong because CH 4 consumption also increases (Verma et al ., ; Harrison et al ., ; Bonnett et al .…”

Effect of Temperature on Oxygen Profiles and Denitrification Rates in Freshwater Sediments

“…Recent studies indicate that within freshwater sediments and phototrophic biofilms, warming can strongly increase denitrification rates (Bonnett et al 2013), due to temperature-regulated oxygen concentrations Bouletreau et al 2012). However, in these studies oxygen concentrations were measured in the water column, whereas most denitrification takes place in the sediment.…”