Biochar interacts with soil type to effect prairie community structure

Background/Question/Methods

Biochar is a carbon-rich material similar to charcoal that is produced when biomass undergoes pyrolysis for bio-oil production.  The pyrolysis-biochar platform is an emerging bioenergy production system that is being developed to address multiple goals of renewable fuel production, recycling nutrients, enhancing soil quality, and reducing net carbon efflux.  When introduced into arable soil, biochar may increase soil organic C levels, cation exchange capacity and crop productivity. However, there are few studies concerning the effect of biochar in perennial communities.  We used greenhouse mesocosms to measure the effect of weathered biochar (2% w/w) on prairie communities. The biochar produced by fast pyrolysis from hardwood sawdust contained 69% C, 0.3% N and 8.5% ash.  A concurrent experiment addressed the effect of biochar the degree of weathering in a single soil type.  The first experiment compared community development in three soil types (2 field soils and potting mix) with biochar that had been aged in the soils for 12 weeks prior to the experiment. The second experiment included a single soil type and three aging treatments, where biochar had been aged in a soil with plants, aged in a soil without plants, and freshly mixed.  

Results/Conclusions

In the first experiment, biochar had no effect on aboveground biomass, the relative density of exotic species, or percent root colonization by mycorrhizal fungi.  However, biochar reduced belowground biomass, grass density, and exotic species richness in all soil types.   The density of forbs and legumes and plant diversity were affected by the interaction of biochar and soil type; where these responses were reduced by biochar in the field soils, but there was no effect of biochar in the potting mix.  Nematodes were only characterized in the field soils. In both cases, biochar increased the relative density of bacteria-feeding nematodes.  Nematode family richness and relative density of omnivores were reduced by biochar in one soil type, but were not affected in the other. In the second experiment, there were no significant interactions of biochar and its age, which . The main effect of aging was only important for nematodes.  The soils that aged with plants had a larger and more complex nematode community than other treatments. Further study on the mechanism behind these multi-trophic effects is of biochar is necessary prior to its widespread application.