Earthworm-induced N _2O emissions in a sandy soil with surface-applied crop residues

摘要

Earlier research with endogeic and epigeic earthworm species in loamy arable soil has shown that both earthworm groups can increase nitrous oxide (N _2O) emissions, provided that crop residue placement matches the feeding strategy of the earthworm ecological group(s). However, it is not yet clear whether these effects also occur in sandy soils which typically contain less soil organic matter and have low soil aggregation levels. Here, we aimed to quantify N _2O emissions as affected by endogeic and/or epigeic earthworm species, and to relate changes in N _2O emissions to earthworm-induced changes in soil properties in a sandy soil. A 90 day mesocosm study was conducted with sandy soil and ~(15)N-labeled radish (Raphanus sativus cv. Adagio L.) residue applied on top. Treatments included: (i) no earthworm addition, (ii) addition of the endogeic species Aporrectodea caliginosa (Savigny), (iii) addition of the epigeic species Lumbricus rubellus (Hoffmeister), and (iv) both species combined. An additional treatment was included without earthworms and with residue manually incorporated into the soil. L. rubellus significantly increased cumulative N _2O emissions from 228 to 859μg N _2O-Nkg ~(-1) (F _(1,12)=83.12, P<0.001), whereas A. caliginosa did not affect N _2O emissions. In contrast to earlier studies in loamy soil, no positive interaction between both species with regard to N _2O emissions was found. This was probably related to high competition for organic resources in the relatively poor soil and a low potential for stable soil aggregate formation (and associated anaerobic microsites) by endogeic worms in sandy soil. ~(15)N isotope analysis revealed that the activity of L. rubellus significantly increased (F _(1,12)=6.20, P=0.028) the recovery of ~(15)N in the 250-8000μm size fraction, indicating incorporation of crop residues into the mineral soil. When residues were manually incorporated, N _2O emissions were significantly (P<0.008) lower (509μg N _2O-Nkg ~(-1)) than when incorporated by L. rubellus. The high N _2O emissions in the presence of L. rubellus, when compared to manual mixing, suggest a stimulation of microbial activity and/or changes in the microbial community composition. Insights on the earthworm effects on N _2O emission from such soils are discussed.