Biodiversity of plants and fauna: the missing link in N2O research?

Jan Willem Van Groenigen1, Diego Abalos2, Imke Kuiper1, Madhav P. Thakur1, George Giannopoulos3, Ingrid M. Lubbers1, Gerlinde B De Deyn1
1 Department of Soil Quality, Wageningen University, The Netherlands
2 ETSI Agronomos, Technical University of Madrid, Spain
3 School of Biological Sciences, University of East Anglia, UK

Invited Talk 5 in Linking biodiversity and biogeochemistry

15.07.2014, 10:00-10:30, H19

Agricultural soils are the dominant source of anthropogenic emissions of the greenhouse gas nitrous oxide (N2O), which is produced by various microbial pathways. Although the ultimate cause of N2O emissions is the increased nitrogen (N) input in modern agriculture, soil parameters affect N2O production as well. These include C availability, anaerobicity and pH. Most traditional management measures to reduce N2O emissions (e.g. fertilization, residue management or irrigation) are aimed at affecting one or more of these parameters. However, N2O emissions remain notoriously difficult to predict and control. Here, we show in three studies that abundance and diversity of higher soil organisms can play an important and hitherto ignored role in N2O emissions. 

In the first study, we tested whether N2O emissions are dependent on grass species richness and/or species identity. We measured N2O emissions from monocultures and two- and four-species mixtures of common grass species with different functional traits. We found no relation between plant species richness and N2O emissions. However, emissions were significantly reduced in specific plant species combinations. The most effective species mixture for N2O reduction depended on the soil nutrient status. Reduced emissions up to 44% in multi-species combinations could be explained by total biomass productivity and by complementarity in root morphology.

In the second study, we studied the effect of functional earthworm diversity on N2O emissions from decomposing crop residue. When residue was applied on the soil surface, no effect of the endogeic earthworm Aporrectodea caliginosa (which feeds on subsoil carbon sources) could be detected. However, in the presence of the epigeic earthworm Lumbricus rubellus (which feeds on topsoil carbon sources and mixes them into the soil) presence of A. caliginosa increased N2O emissions with 51% (P < 0.001). Effects of earthworm species and their interactions on N2O emissions could be explained by their feeding ecology.

In the third study, we quantified the effect of within- and between-trophic level diversity on N2O emissions from decomposing residue. We assembled different soil food webs consisting of soil microbes, various fungivorous fauna and predatory mites. Presence of enchytraeids increased N2O emissions with 238%, and presence of collembolans delayed the peak of N2O emissions. Addition of predatory mites to microcosms with enchytraeids and fungivorous mites (which they prey upon) increased N2O emissions with 460% (p < 0.001). Our observations could be partly explained by a combination of trophic interactions and changes in soil structure.

We conclude that presence and biodiversity of higher soil organisms can control N2O emissions through a variety of within- and between-trophic level interactions. Our results underline the pivotal role that ecology plays in the soil biogeochemical cycle and may point the way towards novel mitigation strategies.

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last modified 2014-04-08