Benjamin M. Rau, Dale W. Johnson, Robert R. Blank, Annmarrie. Lucchesi, Todd G. Caldwell, Eugene W. Schupp,
Transition From Sagebrush Steppe to Annual Grass (Bromus tectorum): Influence on Belowground Carbon and Nitrogen,
Rangeland Ecology & Management, Volume 64, Issue 2, 2011, Pages 139-147, ISSN 1550-7424, https://doi-org.colorado.idm.oclc.org/10.2111/REM-D-10-00063.1
Summary:
In this study, Rau and colleagues examine the impact of cheatgrass (Bromus tectorum) invasion on belowground carbon (C) and nitrogen (N) storage in sagebrush steppe ecosystems, one of the most threatened ecosystems in North America. This study quantifies total belowground C and N changes across multiple sites with varying degrees of cheatgrass invasion. Seven sagebrush steppe sites across the western U.S. were selected, representing a range of soil, vegetation, and climate conditions. Within each site, subplots were categorized by the level of cheatgrass invasion (low, moderate, and high) based on its relative cover compared to other herbaceous plants. Soil cores were collected from the surface to 90 cm depth, and both the soil and roots were analyzed for total C and N content. The study found that the total belowground organic carbon (OC) loss with cheatgrass invasion was estimated at 6–9 Mg·ha⁻¹, nearly double the amount of OC loss from above ground OC. Trends by depth and invasion level showed that soil OC decreased with increasing cheatgrass cover, while root biomass OC increased with higher cheatgrass cover. Additionally, soil OC and root OC decreased with depth as expected. No statistically significant changes in total soil nitrogen were found with cheatgrass invasion, but there was a trend of lower nitrogen content at depth in heavily invaded plots. These findings suggest that cheatgrass invasion affects the distribution of organic carbon in sagebrush steppe ecosystems, potentially influencing long-term soil health and ecosystem function.
Take-home Points:
- The total belowground organic carbon loss with cheatgrass invasion is estimated at 6–9 Mg·ha⁻¹, nearly twice the estimated above ground organic carbon loss from sagebrush conversion.
- Cheatgrass invasion in sagebrush steppe can reduce soil organic carbon storage deep in the soil profile, with greater reductions under high cheatgrass abundance . This study highlights the importance of sampling deeper soil layers (beyond 60 cm) to gain a better understanding of carbon storage and how invasive species impact soil nutrient cycles.
- In cases where deep-rooted native shrubs in sagebrush steppe are replaced with shallow-rooted annual grasses by competition or fire, we can expect greater losses of carbon from the soil.
Management Implications:
- With rising CO2 emissions over the past century, understanding how invasive species affect organic carbon storage is crucial for assessing and managing carbon in a changing climate.
- The loss of belowground organic carbon with cheatgrass invasion suggests that managing cheatgrass could help preserve the soil's carbon storage capacity.