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

Diurnal pattern of nitrous oxide emissions from soils under different vertical moisture distribution conditions

“…The WFPS at the 0-12 cm soil depth on 17 June, 1 July, and 22 July was 46% to 59%, 26% to 60%, and 20% to 47%, respectively, but N2O fluxes decreased gradually on these dates perhaps because N2O emissions increased with increased soil moisture within a certain range of soil WFPS (Peng et al, 2009;Pimentel et al, 2015) (Figures 1d, 1e, and 1f). The maximum N2O flux (3677.4 μg N2O m -2 h -1 ) was observed on 17 June when WFPS (46% to 59%) at the 0-12 cm soil depth was within the reported optimal soil WFPS range (45% to 75%) for peak N2O emissions (Bateman and Baggs, 2005;Khalil and Baggs, 2005;Sey et al, 2008;Castellano et al, 2010;Laville et al, 2011). Simultaneously, the daily mean temperature of 34.1 °C was also within the reported optimum temperature range (25 to 35 °C) for the high nitrification and denitrification reaction .…”

Mineral nitrogen dynamics in the casts of epigeic earthworms (Metaphire hilgendorfi: Megascolecidae)

“…Fresh conical earthworm casts at the soil surface produced by Lumbricid and Glossoscolecid earthworms (Lumbricus terrestris and Martiodrilus carimaguensis) have been shown to have high concentrations of ammonium-nitrogen (NH þ 4 -N) with rapid nitrification during the first week after defecation, and rapid decrease in NH þ 4 -N and nitrate-nitrogen (NO À 3 -N) concentration by rapid nitrification and diffusion after two weeks (Decaëns et al 1999;Mariani et al 2007a). Nitrification rates in granular aggregates formed by Aporrectodea caliginosa, A. tuberculata, Octolasion tyrtaeum (Lumbricidae) and Pontoscolex corethrurus (Glossoscolecidae) were also higher than surrounding soils (Lavelle and Martin 1992;Aira et al 2003;Parkin and Berry 1994) because the aggregate contained rich NH þ 4 -N and aggregate surface provided aerobic micropore environments for microorganisms (Hoffmann et al 2007;Sey et al 2008). Fresh earthworm casts are rich in nutrient and are thus hotspots of microbial activity.…”

“…In our experiment, SOM might not have been exposed despite crushing. Soil organic matter (SOM) bound with clay in the 53 mm microaggregate size range led to possible long-term stabilization of soil C (Six et al 2002;Six et al 2004;Bossuyt et al 2005) and aggregate surface provided aerobic micro-pore environments for microorganisms (Hoffmann et al 2007;Sey et al 2008), thus it is probable that the cast of Metaphire hilgendrfi have aerobic environments and gentle crushing did not destroy the microaggregates in our samples.…”

Connecting silvan and lacustrine ecosystems: transport of carbon from forests to adjacent water bodies

“…Anoxic condition can especially be found in soils saturated with water, but in aerated soils there can also be anaerobic niches (Sey et al 2008). In the absence of oxygen, CO 2 can be used as an electron acceptor in respiration, and CH 4 is produced.…”