Assessment of shrub encroachment on belowground carbon dynamics in tallgrass

Abstract

Changes in fire frequency have allowed native woody shrub species to encroach on native herbaceous tallgrass prairie in the Great Plains of North America. Although these shrub species are native to this ecosystem, their abundance and distribution have increased dramatically due to different changes in land use and land management. We examined vegetative type and microhabitat type effects on decomposition rates and soil CO2 efflux under a representative tallgrass species, Sorghastrum nutans (Indian grass), and shrub species Cornus drummondii (rough-leaf dogwood) at the Ross Natural History Reservation in Americus, Kansas. Shrub microhabitats had greater decomposition rates than tallgrass microhabitats and thus decreased C storage. Rough-leaf dogwood litter had faster decomposition rates than Indian grass litter. Tallgrass litter contained higher levels of lignin and cellulose thus slowing their decomposition rate. Soil respiration rates were not different between grass and shrub habitats. Shrub litter and tallgrass litter had different carbon isotope values, δ13C; however, soil organic matter δ13C was not different between habitat types. This suggests that soil organic matter under shrub habitats may be a legacy effect from previous tallgrass conditions. These results suggest that shrub encroachment in tallgrass prairie could result in less soil carbon storage in the long term. Changes in land management, primarily the inclusion of fire, should reduce shrub encroachment while promoting tallgrass species. The promotion of tallgrass prairie species could help offset rising atmospheric CO2 levels by increasing soil carbon storage.