Functional Diversity of Plants and Soil Fauna As an Important Control of N2o Emissions.

Agricultural soils are the dominant source of anthropogenic emissions of the greenhouse gas nitrous oxide (N₂O). Emissions are related to soil parameters such as N and C availability, anaerobicity and pH. Soil biota can change N₂O emissions indirectly by affecting these controlling soil parameters. Hitherto, most research on N₂O emissions was aimed at the relation between the soil microbial community and N₂O fluxes. Here we show that diversity of higher soil organisms such as plants and fauna can exert important controls over N₂O emissions as well.
In a first study we used a plant functional trait approach to study the relation between plant species strategies and N₂O emissions from fertilized soils. In a greenhouse experiment using monocultures of six grass species with different above- and below-ground traits, we found that acquisitive species reduced N₂O emissions, produced higher total biomass and showed larger N uptake. Acquisitive species had 87% lower N₂O emissions per unit of N uptake than conservative species. Structural equation modelling revealed that specific leaf area and root length density were key traits regulating the effects of plants on N₂O emission and biomass productivity.

In a second study we linked functional diversity of soil fauna to N₂O emissions in a 120-day incubation experiment with eight different species belonging to four different taxonomic groups (collembolans, earthworms, potworms and mites). Functional composition of the soil faunal community was key to explaining faunal-induced emissions: large ecosystem engineers such as earthworms were keystone species driving N₂O emission. The co-presence of other saprotrophic soil biota led to diminished faunal-induced N₂O emissions.
We conclude that biodiversity of higher soil organisms can control N₂O emissions through a variety of trophic and non-trophic interactions. Our results underline the pivotal role that ecology plays in the soil biogeochemical cycle and may point the way towards novel mitigation strategies.