Biochar amendment of grassland soil may promote woody encroachment by Eastern Red Cedar

Although carbon (C) additions to soil have been used in restoration to combat invasive species through changes in soil nitrogen (N) availability, carbon amendments to soil derived from plant material can impact soil N availability in a species-specific manner. As such, amendment-driven feedbacks on N may impact invasive species success and woody encroachment. Soil amendments like biochar, which is often added to soil to increase C storage in grassland systems, may unintentionally encourage woody encroachment into these grasslands by changing soil N dynamics. Few studies have examined biochar impacts on non-agricultural species, particularly invasive species. Woody encroachment of Eastern Red Cedar (Juniperus virginiana) into grasslands provides an ideal context for examining the impact of biochar in grasslands. In the greenhouse, we examined the effect of biochar or leaf litter derived from native and exotic grasses on J. virginiana seedling growth. Juniperus virginiana seedlings grew 40% bigger in biochar amended soil as compared to seedlings grown in litter amended soil. Additionally, we found a more than 2 order of magnitude increase in available NH4+ in the biochar treatments compared to the litter amended soils. Furthermore we found that biochar feedstock type did not have an impact on the effect of biochar, as both native and exotic grass biochar had similar impacts on soil N levels and J. virginiana growth. Our work suggests that once grassland litter is converted to biochar, species impacts on soil N may disappear. In conclusion, our data suggests soil amendments of biochar may encourage woody encroachment into grasslands.