Page Banner

United States Department of Agriculture

Agricultural Research Service

Research Project: Ecological Interactions in Integrated and Biologically-Based Management of Invasive Plant Species in Western Rangelands

Location: Great Basin Rangelands Research

Title: Impacts of insect biological control on soil N transformations in Tamarix-invaded ecosystems in the Great Basin, USA

Authors
item Uselman, Shauna
item Snyder, Keirith
item Blank, Robert

Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 20, 2012
Publication Date: January 2, 2013
Citation: Uselman, S.M., Snyder, K.A., Blank, R.R. 2013. Impacts of insect biological control on soil N transformations in Tamarix-invaded ecosystems in the Great Basin, USA. Journal of Arid Environments. 88:147-155.

Interpretive Summary: Understanding the impacts of insect biological control of saltcedar on soil nitrogen availability is important because changes to N supply could alter future plant composition. We investigated short-term and longer-term impacts of insect herbivory by the northern tamarisk beetle on soil N availability by surveying soils (including the litter layer and surface layer of mineral soil) from three sites and assaying for potential net N mineralization using laboratory incubations as an index of soil N availability. Results partially supported our hypothesis that beetle herbivory would result in increased soil N supply in the short-term (i.e. in the first year of exposure to herbivory), but did not support our hypothesis that beetle herbivory would result in a sustained increase in soil N supply in the longer-term (i.e. after several years of exposure). Short-term effects of herbivory differed by site, and were likely influenced by differences in site fertility. In the longer-term, there was no impact on overall rates of soil N supply, even though there was a trend towards lowered rates of N supply in the mineral soil with more years of herbivory. This trend in the mineral soil may be attributable to declining inputs of plant-derived organic matter to soil due to reduced plant growth resulting from herbivore-induced stress. These results suggest that soil N availability will increase in the short-term and eventually decrease in the longer-term at low fertility sites, while soil N availability will not be impacted by beetle herbivory at high fertility sites.

Technical Abstract: Understanding the impacts of insect biological control of Tamarix spp. on soil nitrogen (N) transformations is important because changes to N supply could alter plant community succession. We investigated short-term and longer-term impacts of herbivory by the northern tamarisk beetle (Diorhabda carinulata) on soil N availability in Tamarix-invaded ecosystems by surveying soils (organic horizon and mineral soil, 0-10 cm) from three sites and assaying for potential net N mineralization using laboratory incubations as an index of soil N availability. Results partially supported our hypothesis that beetle herbivory would result in stimulated rates of net N mineralization in the short-term (i.e. in the first year of exposure to herbivory), and did not support our hypothesis that beetle herbivory would result in a sustained increase in net N mineralization rates in the longer-term (i.e. after several years of exposure). Short-term effects of herbivory differed by site, and were likely influenced by differences in the prevailing soil N status. In the longer-term, there was no impact on overall net N mineralization rates, even though there was a trend towards greater N immobilization in the mineral soil with more years of herbivory. This trend in the mineral soil may be attributable to declining organic matter inputs to soil due to progressive growth limitation from herbivore-induced stress. These results suggest that soil N availability will increase in the short-term and eventually decrease in the longer-term at low fertility sites, while soil N availability will not be impacted by beetle herbivory at high fertility sites.

Last Modified: 7/25/2014