04229naa a2200181 a 450000100080000000500110000800800410001910000190006024500930007926000090017252034480018170000210362970000160365070000160366670000180368270000260370077303210372613148952008-09-22       2008    bl uuuu     u00u1 u    #d1 aLUBBERS, I. M.  aTrade-offs between N2O emission and C-sequestration in the soilbthe role of earthworms.  c2008  aThe rapidly rising concentrations of the greenhouse gas carbon dioxide (CO2) in the atmosphere has spurred the interest in soils as a potential carbon (C) sink. The sequestration of C in soils and vegetation has therefore received much attention and an overwhelming amount of research has recently been aimed at increasing soil organic C stocks. However, there are many reports indicating that C-sequestration is often negated by elevated emissions of the potent greenhouse gas nitrous oxide (N2O). This trade-off mechanism is especially relevant in agro-ecosystems, where C-sequestration is thought to be most promising, but where conversely almost half of anthropogenic N2O-emissions originate from. It is not yet clear what the driving factors behind this trade-off are, nor how it can be avoided. We suggest that earthworm activity may be partly responsible for the trade-off. Earthworm activity is increasingly recognized as being beneficial to C-sequestration through stabilization of SOM. We report results from two laboratory experiments indicating that earthworm activity can also lead to strongly elevated N2O-emissions. In a first experiment, dried grass residue (Lolium perenne) was applied at the top of a loamy soil or mixed through the soil, and N2O-emission was followed for three months. Treatments included presence of the epigeic earthworm Lumbricus rubellus and the anecic earthworm Aporrectodea longa. Cumulative N2O-emissions increased significantly for both species. The strongest effect was measured for L. rubellus, where N2O-emissions significantly increased from 55.7 to 789.1 ìg N2O-N kg-1 soil. This effect was only observed when residue was applied on top of the soil. In a second experiment we determined the effect of epigeic (L. rubellus) and endogeic (Aporrectodea caliginosa) earthworms on N2O-emissions for two different soil types (loam and sand) in the presence of radish residue (Raphanus sativus subsp. oleiferus). Both species showed significant increases in N2O-emissions, which differed with residue application method and soil type. N2O-emissions were generally larger in loamy soils and the strongest effect was measured for A. caliginosa when residue was mixed into the soil, increasing emissions from 1350.1 to 2223.2 ìg N2O-N kg-1 soil. L. rubellus only resulted in elevated N2O-emissions when residue was applied on top. These studies make it clear that elevated N2O-emissions due to earthworm activity is a widespread phenomenon which is associated with all three functional earthworm groups. Also, there are strong indications that interaction effects (both positive and negative) are taking place between earthworm species with respect to N2O-emissions. However, many aspects remain to be determined before we will fully understand the relation between earthworm activity and N2Oemissions. Our future research will focus on: i) quantifying to what extent the earthworm effect is present in functioning (grassland) agro-ecosytems; ii) distinguishing between a ?species effect? and an ?earthworm density effect?; iii) characterizing interactions between functional groups; iv) identifying the exact mechanism through which earthworms increase N2O-emissions, and v) to relate increased N2O-emissions to increased C stabilization through earthworms. Ultimately, our research should make the link between biodiversity (of earthworms) and ecosystem functioning (the soil greenhouse gas balance).1 aGIANNOPOULOS, G.1 aRIZHIYA, E.1 aBERTORA, C.1 aBRUSSAARD, L.1 aGROENIGEN, J. W. van.  tIn: INTERNATIONAL COLLOQUIUM ON SOIL ZOOLOGY, 15; INTERNATIONAL COLLOQUIUM ON APTERYGOTA, 12., 2008, Curitiba. Biodiversity, conservation and sustainabele management of soil animal: abstracts. Colombo: Embrapa Florestas. Editors: George Gardner Brown; Klaus Dieter Sautter; Renato Marques; Amarildo Pasini. 1 CD-ROM.