Emission of nitrous oxide and dinitrogen by diverse earthworm families from Brazil and resolution of associated denitrifying and nitrate-dissimilating taxa

Abstract

The anoxic earthworm gut augments the activity of ingested microorganisms capable of anaerobiosis. Small earthworms (Lumbricidae) emit denitrification-derived N(2)O, whereas the large Octochaetus multiporus (Megascolecidae) does not. To examine this paradox, differently sized species of the families Glossoscolecidae (Rhinodrilus, Glossoscolex, Pontoscolex), Megascolecidae (Amynthas, Perionyx), Acanthodrilidae (Dichogaster), and Eudrilidae (Eudrilus) from Brazil were analyzed. Small species and the large Rhinodrilus alatus emitted N(2)O, whereas the large Glossoscolex paulistus did not, even though its gut could denitrify. N(2) and N(2)O were emitted concomitantly, and R. alatus emitted the highest amount of N(2). Denitrifiers and dissimilatory nitrate reducers were analyzed by barcoded amplicon pyrosequencing of narG, nirK, and nosZ. Gene sequences in gut and soil of the large G. paulistus were similar, whereas sequences in gut and soil of the small Amynthas gracilis were different and were also different compared with those of the gut and soil of G. paulistus. However, the denitrifying gut microbiota for both earthworms appeared to be soil-derived and dominated by Rhizobiales. The results demonstrated that (1) the emission of denitrification-derived N(2)O is widespread in different earthworm families, (2) large earthworms can also emit nitrogenous gases, and (3) ingested members of Rhizobiales are associated with this emission.

Disentangling the influence of earthworms in sugarcane rhizosphere

“…Experiments have repeatedly demonstrated that N 2 O emissions are associated with microbial processes happening in the gut19 and worm-worked soils37, where the populations of denitrifiers and dissimilatory nitrate reducers can be more abundant than in bulk soil18. Furthermore, the physical process of ingesting microbial cells might kill some of them, releasing N trapped in microbial biomass.…”

“…Additionally, the in situ conditions of earthworm guts are likely to favor denitrification. N 2 O and N 2 emissions from earthworms and denitrification genes were reported to be enriched in the alimentary canal of earthworms19. Likewise, the products of metabolic processes happening in the gut can be released in the soil20212223 and benefit microbial communities living even beyond the drilosphere24.…”

Methanogenic food web in the gut contents of methane-emitting earthwormEudrilus eugeniaefrom Brazil

“…The in situ conditions of the gut stimulate ingested obligate anaerobes and facultative aerobes that promote diverse fermentations along the alimentary canal, and fermentation-derived molecular hydrogen (H 2 ) is emitted in vivo by earthworms (Karsten and Drake, 1995;Schmidt et al, 2001;Wü st et al, 2009aWü st et al, , 2011. Fermentation products in the gut may serve as substrates for soil-derived denitrifiers and be trophically linked to the in vivo emission of nitrous oxide (N 2 O) and dinitrogen (N 2 ) (Karsten and Drake, 1997;Matthies et al, 1999;Depkat-Jakob et al, 2013). In this regard, earthworms can contribute to the capacity of soils to emit nitrogenous gases (Karsten and Drake, 1997;Matthies et al, 1999;Rizhiya et al, 2007;Lubbers et al, 2011), and it has been postulated that the emission of H 2 by earthworms might drive energy-dependent processes in soil such as the fixation of N 2 or carbon dioxide (CO 2 ) (Wü st et al, 2009a).…”

Nitrification inhibitors mitigate earthworm-induced N2O emission—a mesocosm study

“…The N 2 O concentrations in the gut of Aporrectodea caliginosa and Lumbricus rubellus ranged from 0.2 to 17.6 μM . Amynthas gracilis and Pontoscolex corethrurus led to 10.7 and 11.6 nmol N 2 O g (fresh weight) −1 emissions from a grassland soil (Depkat-Jakob et al 2013). In a mesocosm study using a sandy soil, Giannopoulos et al (2011) found that L. rubellus increased cumulative N 2 O emission from 228 to 859 μg N 2 O-N kg −1 after 90 days.…”

“…Bertora et al (2007) reported that the incorporation of Aporrectodea longa into soil increased N 2 O emission by approximately 30 % from 3 to 12 days. It has been suggested that earthworms themselves, their casts, and drilosphere can be a source of N 2 O emissions and that earthworm-induced N 2 O emissions are mainly due to the enhanced nitrification in soil Karsten and Drake 1997;Elliott et al 1991) and denitrification in earthworm gut (Depkat-Jakob et al 2013;Majeed et al 2013). According to Giannopoulos et al (2011), earthworm-induced N 2 O emission may be due to the earthworms' stimulation of microbial activity and/or changes in the microbial community composition.…”