Processes Regulating Soil Emissions of NO and N^2O in a Seasonally Dry Tropical Forest

Abstract

While much is known about control of production of NO and N2O by nitrifying and denitrifying bacteria at the cellular level, application of this knowledge to field studies has not yielded unifying concepts that are widely applicable and that foster understanding of global sources of these atmospheric trace gases. We applied a simple conceptual model to the investigation of sources of NO and N2O and the environmental factors affecting fluxes in a drought—deciduous forest of Mexico. Fluxes of NO and N2O were higher in the wet season than the dry season, but addition of water to dry soil caused large pulses of CO2, NO, and N2O emissions. Immediate increases of extractable soil NH4+ and high rates of gross N mineralization and gross nitrification also were observed following wetting of dry soil NO2— had accumulated during the dry season, and that NO2— plus the pulse of increased soil NH4+ were mostly consumed within 24 hours of wetting. This dynamic microbial processing of soil inorganic N coincided with the pulses of NO and N2O production following wetting of dry soil. Acetylene inhibition experiments indicated that NO production was dependent on nitrification, that nitrification was the dominant source of N2O when the soil was wetted at the end of the dry season, and that dentrification might be an important source of N2O during the wet season. Post—wetting soil moisture was correlated negatively with NO fluxes and positively with N2O fluxes. These results support a conceptual model in which N trace gas production is generally constrained by the rates of N mineralization and nitrification, while the specific ratios of NO and N2O fluxes and the contributions from nitrifying and denitrifying bacteria are controlled largely by soil moisture.

Controls on soil nitrogen oxide emissions from forest and pastures in the Brazilian Amazon

“…Acetylene inhibition experiments conducted in intact cores taken from this Mexican forest failed to inhibit N20 production in soil cores taken during the wet season with 14% WFPS. Because acetylene inhibits nitrification, failure to inhibit N20 production clearly indicates denitrification is the main process contributing to the production of this trace gas at this site [Davidson et al, 1993]. In our forest soils an increase in heterogeneity of WFPS among soil macrosites can account for denitrification because NO3-produced in one site can move to another site where it is denitrified.…”

“…Denitrification has been shown to occur even in very dry soils. For example, experiments conducted in a seasonally dry deciduous tropical forest of Mexico [Davidson et at., 1993] demonstrated that even in the very course-textured soil of this forest, where soils moisture content never exceed 20%, denitrification was a modest contributor of N20 emissions. Acetylene inhibition experiments conducted in intact cores taken from this Mexican forest failed to inhibit N20 production in soil cores taken during the wet season with 14% WFPS.…”

Denitrification and indirect N2O emissions in groundwater: Hydrologic and biogeochemical influences

“…Von der argued that a drop in the GWT causes a decrease in N 2 O-N production whereas recharge stimulates N 2 O-N production. Recharge can increase groundwater DO, DOC and NO 3 --N resulting in increased N 2 O-N production and could decrease further N 2 O-N reduction (Davidson, et al, 1993). Deurer et al (2008) …”

Effect of land use on soil nutrients in the loess hilly area of the Loess Plateau, China

“…Land use change, for example, from natural vegetation to agricultural land, or from grassland to arable land, can strongly impact soil carbon and nutrient concentrations. This is because (1) human activities, such as tillage, harvest and vegetation plantation, could affect soil nutrient decomposition or loss; (2) human disturbance may affect soil moisture by changing micro-climate and plant patterns (Davidson et al, 1993); and (3) species have different nutrient requirements, exploit nutrients with varying efficiency and store or convert nutrients at different rates (Aerts and Chapin, 2000). Changes in land use affect input and output of nutrients and carbon in soils and vegetation.…”