Functional diversity of soil invertebrates: a potential tool to reduce N2O emission?

Soil biota play a crucial role in the mineralization of nutrients from organic material. However, they can thereby increase emissions of the potent greenhouse gas nitrous oxide (N2O). Our current lack of understanding of the factors controlling N2O emissions is impeding the development of effective mitigation strategies. The challenge is to control N2O emissions from production systems without reducing crop yield. Diversity of soil fauna may play a key role: high functional diversity of soil invertebrates (FDSI) is known to stimulate nitrogen mineralisation and thereby plant growth. It is still unknown whether high FDSI can concurrently diminish N2O emissions. Experimental studies are contradictory, reporting both increasing and decreasing emissions by single faunal species. However, faunal species occur in communities of interacting species. We will therefore study the effect of FDSI on N2O emissions from agricultural soils. We hypothesize that increased FDSI decreases N2O emissions by facilitating more complete denitrification through 1) stimulating the activity of denitrifying microbes; and 2) affecting the distribution of micro and macro pores, creating more anaerobic reaction sites. To test this hypothesis, we will establish invertebrate food webs in soil microcosms with different levels of functional diversity. We will use state-of-the-art molecular analysis to quantify denitrifier gene expression, and X-ray tomography to analyse fine-scale changes in soil structure. This integration of soil biological and -physical impacts on N2O emissions will enable us to resolve whether FDSI can promote nitrogen mineralisation without increasing N2O emissions. This is essential for the development of effective mitigation strategies.