|Rau, Benjamin -|
|Johnson, Dale -|
|Lucchesi, Annmarie -|
|Caldwell, Todd -|
|Schupp, Eugene -|
Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 7, 2010
Publication Date: March 1, 2011
Citation: Rau, B.M., Johnson, D.W., Blank, R.R., Lucchesi, A., Caldwell, T.G., Schupp, E.W. 2011. Transition from sagebrush steppe to annual grass (Bromus tectorum): influence on belowground carbon and nitrogen. Rangeland Ecology and Management. 64:139-147. Interpretive Summary: Global change alters terrestrial vegetation, which affect biogeochemical cycling. Sagebrush is the landscape-dominant shrub over much of the Great Basin, but is being replaced at an alarming rate by the exotic annual grass, cheatgrass. Little is currently known about the distribution of belowground carbon on these changing landscapes, how annual grass invasion affects carbon and nitrogen pools. As part of a Joint Fire Sciences funded project called the Sagebrush Treatment Evaluation Project (SageSTEP), we quantified the spatial distribution of soil organic carbon and nitrogen at 7 sites in Utah, Oregon, Idaho, Nevada, and Washington State USA experiencing varied stages of cheatgrass invasion. Cheatgrass invasion significantly influences the vertical distribution of carbon and nitrogen within the soil profile and may result in decreased organic carbon below 60 cm. Organic carbon and nitrogen associated with coarse fragments accounted for at least 10% of belowground pools and emphasizes the need for researchers to quantify nutrients in coarse fragments.
Technical Abstract: Vegetation changes associated with climate shifts and anthropogenic disturbance have major impacts on biogeochemical cycling. Much of the interior western United States currently is dominated by sagebrush (Artemisia tridentate Nutt.) ecosystems. At low to intermediate elevations, sagebrush ecosystems increasingly are influenced by cheatgrass (Bromus tectorum L.) invasion. Little currently is known about the distribution of belowground organic carbon (OC) on these changing landscapes, how annual grass invasion affects OC pools, or the role that nitrogen (N) plays in carbon (C) retention. As part of a Joint Fire Sciences-funded project called the Sagebrush Treatment Evaluation Project (SageSTEP), we quantified the depth distribution of soil OC and N at seven sites experiencing cheatgrass invasion. We sampled plots that retained sagebrush, but represented a continuum of cheatgrass invasion into the understory. Eighty four soil cores were taken using a mechanically driven diamond-tipped core drill to a depth of 90 cm, or until bedrock or a restrictive layer was encountered. Samples were taken in 15 cm increments, and soil, rocks, and roots were analyzed for OC and total N. We determined that cheatgrass influences the vertical distribution of OC and N within the soil profile and might result in decreased OC content below 60 cm. We also found that OC and total N associated with coarse fragments accounted for at least 10% of belowground pools. This emphasizes the need for researchers to quantify nutrients in deep soil horizons and coarse fragments.