Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/28/2007
Publication Date: 5/1/2007
Citation: Davies, K.W., Pokorny, M.L., Sheley, R.L., James, J.J. 2007. Influence of plant functional removal on inorganic soil nitrogen concentrations in native grasslands. Rangeland Ecology and Management. 60(3):304-310. Interpretive Summary: Plant species are often classified into functional groups based on similar characteristics. Functional groups are presumed to use resources different from one another and therefore, high plant functional group diversity has been suggested to decrease resource availability. Maintaining low resource availability is critical to preventing weed invasions. However, evidence of high plant functional diversity reducing resource availability is generally lacking. We investigated the impacts of removing functional groups on soil inorganic nitrogen concentrations. Removing functional groups increased soil inorganic nitrogen concentrations. The increase in inorganic nitrogen concentrations depended on which functional group was removed and often the interaction between season and which functional group was removed. These results demonstrated high functional group diversity was important to maintaining low soil inorganic nitrogen concentrations. This study illustrates the importance of managing for functional group diversity and suggests revegetation with multiple functional groups may be more successful because of greater resource use.
Technical Abstract: High plant functional group diversity has been suggested to reduce resource concentrations based on the assumption that species from one functional group acquire resources similarly to one another, while species from other functional groups acquire resources dissimilarly. Soil nutrient concentrations may be reduced when functional groups differ in their soil nutrient acquisition patterns. To determine if functional groups use soil nutrients different from one another, we investigated the impact of removing individual functional groups on soil inorganic nitrogen (NO3- and NH4+) concentrations in the Idaho fescue (Festuca idahoensis Elmer)/bluebunch wheatgrass (Pseudoroegneria spicata (Pursh) A. Löve)) habitat type in Montana. Treatments were removing: 1) nothing (control), 2) all plant materials (total removal), 3) shallow-rooted (< 15 cm) forbs, 4) deep-rooted (> 15 cm) forbs, 5) all forbs, 6) grasses, and 7) spikemoss. Inorganic nitrogen was measured at two soil depths (0 - 15 cm and 16 - 40 cm) in the spring, summer, and fall. The removal of individual functional groups generally increased soil NO3- and NH4+ concentrations. Total removal increased NO3- concentrations more than removing individual functional groups. The magnitude of change in soil inorganic nitrogen concentrations depended on which functional group was removed. Effects of removing individual functional groups on soil inorganic nitrogen concentrations frequently varied with season. These results suggest functional groups vary in their soil nutrient acquisition patterns and increased functional diversity decreases soil nutrient availability. Therefore, maintaining or improving functional diversity may be a method to more fully utilize soil nutrients because functional groups can be different in their spatial and temporal acquisition of resources.