Contrasting responses of macro- and meso-fauna to biochar additions in a bioenergy cropping system

Abstract Combining bioenergy land use with biochar production could represent a win-win management strategy to increase energy production whilst reducing greenhouse gas emissions. However, a fuller understanding of the effects that these changes in land use and soil amendment could have on soil biodiversity and processes is needed. We performed a 2-year field experiment to determine the consequences of adding three different amounts of biochar (10 t ha−1, 25 t ha−1 and 50 t ha−1) to a commercial Miscanthus bioenergy plantation on soil invertebrate community structure and abundances of enchytraeids, collembolans, mites and earthworms. We also used stable isotope analyses to determine shifts in feeding preferences and to quantify C assimilation by those soil organisms most likely to be affected by soil amendments (i.e. soil ingesters: earthworms and enchytraeids). Results showed that biochar additions to the soil had a negative effect on larger-sized soil fauna (earthworms) significantly reducing their population sizes and species richness whereas, in contrast, mesofauna appeared to benefit from the input of the biochar. Although significant assimilation of new C by anecic earthworms was observed, it was clearly insufficient to support population growth and, more importantly, the dominant ecological group in these agricultural soils (endogeics) showed the lowest assimilation values. These results indicate that biochar additions might result in the loss of some of the ecosystem services provided by earthworms, an important concern in these intensively managed agricultural soils. Finally, our findings highlight the need for more field research at species level to fully elucidate the mechanisms driving the biological responses to these types of ecosystem management.