Small-scale heterogeneity in carbon dioxide, nitrous oxide and methane production from aggregates of a cultivated sandy-loam soil

• Published in: Soil biology & biochemistry Vol. 40; no. 9; pp. 2468 - 2473
• Main Authors: Sey, Benjamin K., Manceur, Ameur M., Whalen, Joann K., Gregorich, Edward G., Rochette, Philippe
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.09.2008; New York, NY Elsevier Science
• Subjects: Acetylene; aerobic conditions; agricultural soils; Agronomy. Soil science and plant productions; anaerobic conditions; Biochemistry and biology; Biological and medical sciences; Carbon dioxide; Chemical, physicochemical, biochemical and biological properties; Denitrification; fractionation; Fundamental and applied biological sciences. Psychology; gas emissions; greenhouse gases; heterotrophs; Methane; methane production; microbial activity; Nitrification; Nitrous oxide; oxygen; Oxygen diffusion; particle size; Physical properties; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Respiration; sandy loam soils; Soil aggregate fraction; soil aggregates; Soil gas production; soil respiration; Soil science; soil water content; spatial variation; Structure, texture, density, mechanical behavior. Heat and gas exchanges; Methane; Soil gas production; Soil aggregate fraction; Carbon dioxide; Nitrification; Denitrification; Nitrous oxide; Oxygen diffusion; Respiration; Acetylene; Oxygen; Small scale; Cultivated soil; Soil structure; Heterogeneity; Soil science; Aggregate; Nitrogen protoxide; Sandy loam soil
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/j.soilbio.2008.05.012

Spatial variability in carbon dioxide (CO 2), nitrous oxide (N 2O) and methane (CH 4) emissions from soil is related to the distribution of microsites where these gases are produced. Porous soil aggregates may possess aerobic and anaerobic microsites, depending on the water content of pores. The purpose of this study was to determine how production of CO 2, N 2O and CH 4 was affected by aggregate size and soil water content. An air-dry sandy loam soil was sieved to generate three aggregate fractions (<0.25 mm, 0.25–2 mm and 2–6 mm) and bulk soil (<2 mm). Aggregate fractions and bulk soil were moistened (60% water-filled pore space, WFPS) and pre-incubated to restore microbial activity, then gradually dried or moistened to 20%, 40%, 60% or 80% WFPS and incubated at 25 °C for 48 h. Soil respiration peaked at 40% WFPS, presumably because this was the optimum level for heterotrophic microorganisms, and at 80% WFPS, which corresponded to the peak N 2O production. More CO 2 was produced by microaggregates (<0.25 mm) than macroaggregate (>0.25 mm) fractions. Incubation of aggregate fractions and soil at 80% WFPS with acetylene (10 Pa and 10 kPa) and without acetylene showed that denitrification was responsible for 95% of N 2O production from microaggregates, while nitrification accounted for 97–99% of the N 2O produced by macroaggregates and bulk soil. This suggests that oxygen (O 2) diffusion into and around microaggregates was constrained, whereas macroaggregates remained aerobic at 80% WFPS. Methane consumption and production were measured in aggregates, reaching 1.1–6.4 ng CH 4–C kg −1 soil h −1 as aggregate fractions and soil became wetter. For the sandy-loam soil studied, we conclude that nitrification in aerobic microsites contributed importantly to total N 2O production, even when the soil water content permitted denitrification and CH 4 production in anaerobic microsites. The relevance of these findings to microbial processes controlling N 2O production at the field scale remains to be confirmed.