General patterns of responses
Increased soil N2O flux following thawing have been observed in cropland (Rochette et al., 2010), grassland (Virkajärvi et al., 2010), forest (Maljanen et al., 2010), marsh (Yu et al., 2007), alpine meadow (Hu et al., 2010), and alpine tundra (Brooks et al., 1997). Laboratory incubation experiments showing similar results have been performed with agricultural (Kurganova et al., 2004), grassland (Yao et al., 2010), forest (Goldberg et al., 2008), permafrost (Elberling et al., 2010), and coastal Antarctica soils (Zhu et al., 2009). Episodic N2O peak fluxes of up to 750 μg N2O−N m–2 h–1 (background levels of under 50 μg N2O−N m–2 h–1) were measured after freeze-thaw in arable field (Dörsch et al., 2004). Such increases usually occur when soil temperatures are close to 0 oC (Christensen and Tiedje, 1990; Chen et al., 1995; Müller et al., 2003). Studies examining the thawing effect on N2O flux have reported 6 to 35 d response following rewetting (Table 2) and N2O fluxes increase up to 17,000% (Table 2, Fig. 2). Thaw-induced N2O fluxes constituted a major component of annual N2O fluxes from arable field (Regina et al., 2004; Johnson et al., 2010), temperate grassland (Kammann et al. 1998; Müller et al., 2002), steppe (Holst et al., 2008; Wolf et al., 2010), wetland (Yu et al., 2007) and forest ecosystems (Papen and Butterbach-Bahl, 1999; Wu et al., 2010a; Guckland et al., 2010) with contributions exceeding 50% of the annual budget in some years.
Mechanisms and drivers
Enhanced microbial metabolism (see §4.1) and changing physical protection have been hypothesized as responsible for increased N2O fluxes following thawing. Increased N2O flux following thawing has been shown to predominantly originate from denitrification (Mørkved et al., 2006; Sharma et al., 2006; Wagner-Riddle et al., 2008). Denitrification contributed 83% of the produced N2O immediately after thawing and 72% after 70 h incubation in undisturbed soil cores (Ludwig et al., 2004). Physical mechanisms involving reduced diffusivity can also influence N2O. Anaerobic water-saturated topsoil conditions are created during thawing by reduced drainage of melting ice and snow in the frozen subsoil, and this conditions are known to increase N2O fluxes (Li et al., 2000; de Bruijn et al., 2009). Ice layers prevent the escape of soluble N2O into the liquid water film and may result in supersaturated soil solutions. During thawing periods, the diffusion barriers disappear, and the trapped N2O is released into the atmosphere within a few days (Goldberg et al., 2010b; Virkajärvi et al., 2010). Increased N2O fluxes following thawing may be caused by the combination of these two mechanisms (Koponen et al., 2006; de Bruijn et al., 2009).
The magnitude of increased N2O flux following thawing of frozen soils is influenced by soil texture (Christensen and Christensen, 1991; Lemke et al., 1998), crop species (Kaiser et al., 1998; Johnson et al., 2010), forest type (Teepe and Ludwig, 2004), tillage history (Singurindy et al., 2009), soil water content (Koponen and Martikainen, 2004; Wolf et al., 2010), and the length of the freezing period (Papen and Butterbach-Bahl, 1999; Wagner-Riddle et al., 2007). Soils with clay-dominated aggregates are prone to high N2O flux during thawing periods (van Bochove et al., 2000; Müller et al., 2003). There is little information on the effect of soil water content on N2O fluxes (Röver et al., 1998; van Bochove et al., 2000). Röver et al. (1998) measured large fluxes of N2O after freezing in an agricultural soil at 80% water-filled pore space, while van Bochove et al. (2000) reported that flux of N2O from a clay soil were significantly larger at a volumetric water content of 39% than at 28%.
A review of field studies shows that N2O emission
ReplyDeleteduring winter/spring thaw is usually greater in annual (1.19+0.79 kg N2O-N /ha/year) than in perennial(0.29+0.39 kg N2O-N/ha/year) cropping systems.
This is likely because there is less inorganic N in soils under perennial crops due to the longer period of active growth and the associated uptake of nutrients, and also to the slower decay of above-ground residues and roots after harvest.
Reference
Soil & Tillage Research 83 (2005) 53–72
Phillips, R.L., Wick, A.F., Liebig, M.A., West, M.S., Daniels, W.L., 2012. Biogenic emissions of CO2 and N2O at multiple depths increase exponentially during a simulated soil thaw for a northern prairie Mollisol. Soil Biology and Biochemistry 45, 14-22.
ReplyDeleteAbstract
The fate of carbon (C) and nitrogen (N) belowground is important to current and future climate models as soils warm in northern latitudes. Currently, little is known about the sensitivity of microbial respiration to temperature changes at depths below 15 cm. We used whole-core (7.6 cm dia. × 90 cm) laboratory incubations to determine if temperature response quotients (Q10) for CO2 and N2O varied with depth for undisturbed prairie while plants were senescent and clipped at the surface. We collected intact soil cores from an undisturbed prairie in central North Dakota and uniformly subjected them to freezing (5 to −15 °C) and thawing (−15 to 5 °C). We measured rates of CO2 and N2O emissions at 5 °C temperature increments at 0, 15, 30, 45, 60, and 75 cm depths. During freezing, active and sterilized core emissions occurred only between 0 and −10 °C. During thawing, a simple first-order exponential model, E = αeβT, fit observed CO2 and N2O emissions (R2 = 0.91 and 0.99, respectively). Parameter estimates for β were not significantly different across depths for CO2 and for N2O (Q10 = 4.8 and 13.7, respectively). Parameter estimates for α (emissions when temperature is 0 °C) exponentially declined with depth for both gases for similar depth-response curves. Stepwise regressions of soil properties on α parameter estimates indicated emissions of CO2 and N2O at 0 °C during thawing were positively correlated (R2 > 0.6) with soil porosity. Results indicate pedogenic properties associated with depth may not necessarily influence temperature response curves during thawing but will affect emissions at 0 °C for both CO2 and N2O.
Highlights
► CO2 and N2O temperature responses did not vary with depth during thawing. ► Emissions at 0 °C decreased exponentially with depth. ► Results suggest soil properties associated with depth control emissions at 0 °C.
Keywords: Carbon dioxide; Nitrous oxide; Q10; Temperature response curve; Freezing; Thawing; Intact core
Luo, G. J., Brüggemann, N., Wolf, B., Gasche, R., and Butterbach-Bahl, K.: Decadal variability of soil CO2 NO, N2O, and CH4 fluxes at the Höglwald Forest, Germany, Biogeosciences Discuss., 8, 12197-12245, doi:10.5194/bgd-8-12197-2011, 2011.
ReplyDeleteBesides agricultural soils, temperate forest soils have been identified as significant sources of or sinks for important atmospheric trace gases (N2O, NO, CH4, and CO2). Although the number of studies for this ecosystem type increased more than tenfold during the last decade, studies covering an entire year and spanning more than 1–2 yr remained scarce. This study reports the results of continuous measurements of soil-atmosphere C- and N-gas exchange with high temporal resolution carried out since 1994 at the Höglwald Forest spruce site, an experimental field station in Southern Germany. Annual soil N2O emission, NO emission, CH4 uptake, and CO2 emission (1994–2010) varied in a range of 0.2–3.2 kg N2O-N ha−1 yr−1, 6.4–11.4 kg NO-N ha−1 yr−1, 0.9–3.5 kg CH4-C ha−1 yr−1, and 7.0–9.2 t CO2-C ha−1 yr−1, respectively. The observed high fluxes of N-trace gases are most likely a consequence of high rates of atmospheric nitrogen deposition (> 20 kg N ha−1 yr−1) of NH3 and NOx to our site. For N2O cumulative annual emissions were > 0.8 kg N2O-N ha−1 yr−1 high in years with freeze-thaw events (5 out 14 yr). This shows that long-term, multi-year measurements are needed to obtain reliable estimates of N2O fluxes for a given ecosystem. Cumulative values of soil respiratory CO2 fluxes were highest in years with prolonged freezing periods e.g. the years 1996 and 2006, i.e. years with below average annual mean soil temperatures and high N2O emissions. The results indicate that long freezing periods may even drive increased CO2 fluxes not only during soil thawing but also throughout the following growing season.
Furthermore, based on our unique database on GHGs we analyzed if soil temperature, soil moisture, or precipitation measurements can be used to approximate GHGs at weekly, monthly, or annual scale. Our analysis shows that simple-to-measure environmental drivers such as soil temperature or soil moisture are suitable to approximate fluxes of NO and CO2 in weekly and monthly scales with a reasonable uncertainty (accounting for up to 80 % of the variance). However, for N2O and CH4 we so far failed to find meaningful correlations and, thus, to provide simple regression models to estimate fluxes. This is most likely due to the complexity of involved processes and counteracting effects of soil moisture and temperature, specifically with regard to N2O production and consumption by denitrification and microbial community dynamics.
Blankinship, Joseph C., and Stephen C. Hart. 2012. Consequences of manipulated snow cover on soil gaseous emission and N retention in the growing season: a meta-analysis. Ecosphere 3:art1. http://dx.doi.org/10.1890/ES11-00225.1
ReplyDeleteAbstract
Most seasonally snow covered ecosystems will continue to face more shallow and discontinuous snowpack as the world warms. Annual greenhouse gas and nitrogen (N) budgets in seasonally snow covered ecosystems are partly controlled by snow depth and duration, but little is known about the generality of these responses during the growing season and the driving mechanisms across sites. Using results from snow addition and removal experiments, we performed a meta-analysis to quantify soil biogeochemical responses during the growing season to decreasing winter snow depth, and to identify correlative variables that best explained changes in carbon dioxide (CO2) efflux, nitrous oxide (N2O) efflux, and mobile N concentration in runoff, leachate, and soil solution. The moderators tested to possibly explain the effects of manipulated snow depth were the sampling date (earlier vs. later in growing season), the direction of snow manipulation, soil texture, vegetation type, mean annual temperature (MAT), mean annual precipitation (MAP), latitude, and the maximum change in winter soil temperature due to snow manipulation. Across studies, decreasing snow depth caused a 35% reduction in soil CO2 efflux and a three-fold increase in N2O efflux later in the growing season, and a two-fold increase in mobile N concentration throughout the growing season. The tested moderators of CO2 and N2O efflux were important earlier but not later in the growing season. Early in the growing season, decreasing snow depth increased soil CO2 efflux in snow removal experiments at lower latitude sites with a higher MAT and smaller change in winter soil temperature. Decreasing snow depth increased N2O efflux more at lower latitudes sites with a higher MAP and smaller change in winter soil temperature. Changes in mobile N concentration were greater in forest than in non-forest ecosystems, and tended to increase with latitude. Our meta-analysis suggests that winter and summer biogeochemistry are intertwined, and decreasing snow cover generally reduces ecosystem N retention. Future changes in snow cover may impact global carbon and N biogeochemistry at the annual scale, likely driven by interactions between climate, latitude, and vegetation type.
Li, K., Gong, Y., Song, W., Lv, J., Chang, Y., Hu, Y., Tian, C., Christie, P., Liu, X., 2012. No significant nitrous oxide emissions during spring thaw under grazing and nitrogen addition in an alpine grassland. Global Change Biology 18, 2546-2554
ReplyDeleteA recent study (Wolf et al., 2010) suggests that short—lived pulses of N2O emission during spring thaw dominate the annual N2O budget and that grazing decreases N2O emissions during the spring thaw. To verify this we conducted year—round N2O flux measurements from June 2010 to May 2011 in Tianshan alpine grassland in central Asia. No pulse emissions of N2O were found at grazing management sites and nitrogen addition sites during the spring thaw. The contribution of the spring thaw to the total annual N2O budget was small and accounted for only 6.6% of the annual fluxes, with winter emissions accounting for 16.7% and growing season emissions accounting for 76.7%. The difference in N2O emissions attributable to grazing management was not significant (P > 0.05). Nitrogen input tended to increase N2O emissions at N addition sites during the grass growing season compared with those at unfertilized sites. N2O fluxes showed a significant correlation with air temperature and also with both soil temperature and soil water content at 10 cm depth.
Glenn, A.J., Tenuta, M., Amiro, B.D., Maas, S.E., Wagner-Riddle, C., 2012. Nitrous oxide emissions from an annual crop rotation on poorly drained soil on the Canadian Prairies. Agricultural and Forest Meteorology 166-167, 41-49
ReplyDeleteAbstract
Agricultural soils are a significant anthropogenic source of nitrous oxide (N2O) to the atmosphere. Despite likely having large emissions of N2O, there are no continuous multi-year studies of emissions from poorly drained floodplain soil. In the present study, the micrometeorological flux of N2O (FN) was measured over three years (2006–2008) in a maize (Zea mays L.)/faba (Vicia faba minor L.)/spring-wheat (Triticum aestivum L.) rotation in the Red River Valley, Manitoba, Canada on a gleyed humic verticol soil. Comparison of newly established reduced and intensive tillage treatments showed no difference in FN within the constraints of the high variability between duplicate plots. The annual gap-filled ΣFN across tillage treatments was 5.5, 1.4, and 4.3 kg N ha−1 in the maize, faba, and spring-wheat crop years, respectively. Emissions from fertilizer N addition and soil thaw the following spring was responsible for the greater ΣFN in the maize and spring-wheat years. Using four approaches to approximate background ΣFN resulted in estimates of 3.5–3.8% and 1.4–1.8% of applied fertilizer N emitted as N2O for the maize and spring-wheat crops, respectively. The CO2 global warming potential equivalent of ΣFN over the three study years was an emission of 5.4 Mg CO2-equiv. ha−1 which adds to the previously determined C balance emission of 11.6 Mg CO2-equiv. ha−1.
Highlights
► N2O emissions occurred at thaw and shortly after fertilizer addition. ► N2O emission were 5.5, 1.4, and 4.3 kg N ha−1 in maize, faba, and spring-wheat years. ► Emissions with faba were lowest because of lack of fertilizer and thaw emissions. ► CO2 equiv. of N2O emissions were comparable to that for net emissions of CO2. ► Net N2O and CO2 emissions resulted in 22.8 Mg CO2-equiv. ha−1 over the three years.
Risk, N., Snider, D. and Wagner-Riddle, C. 2013. Mechanisms leading to enhanced soil nitrous oxide fluxes induced by freeze–thaw cycles. Can. J. Soil Sci. 93: 401–414.
ReplyDeleteThe freezing and thawing of soil in cold climates often produces large emissions of nitrous oxide (N2O) that may contribute significantly to a soil's annual greenhouse gas emission budget. This review summarizes the state of knowledge of the physical and biological mechanisms that drive heightened N2O emissions at spring melt. Most studies of freeze–thaw N2O emissions have concluded that denitrification is the dominant process responsible for the large thaw fluxes. Soil moisture, availability of carbon and nitrogen substrates, and freeze temperature and duration are the major factors identified as controlling freeze–thaw cycle (FTC) N2O emissions. Two mechanisms are proposed to lead to enhanced N2O emissions at thaw: (1) the physical release of N2O that is produced throughout the winter and trapped under frozen surface layers and/or within nutrient-rich water films in the frozen layers, and (2) the emission of newly produced (de novo) N2O at the onset of thaw, which is stimulated by increased biological activity and changes in physical and chemical soil conditions. Early studies implicated the physical release of N2O from subsurface soil layers as the main mechanism contributing to spring thaw emissions, but most current studies do not support this hypothesis. Mounting evidence suggests that most of the emitted N2O is produced de novo. This may be fueled by newly available denitrification substrates that are liberated from dead microbes, fine roots, and/or the disintegration of soil aggregates. The release of N2O trapped in shallow surface layers may represent a small, but important contribution of the total emissions. Application of new techniques to study microbial communities in their natural environments, such as metagenomics and stable isotope studies, have the potential to enhance our understanding of the soil N cycle and its linkages to FTC N2O emissions. Future field studies of N2O emissions ought to quantify both overwinter accumulation/release and the de novo production of N2O so that the contribution of each mechanism to the annual emission budget is known.