Soil carbon and nitrogen as influenced by nitrogen deposition and invasive species in the novel ecosystem of Mount St. Helens
Abstract
The aim of this study was to investigate the link between atmospheric nitrogen (N)-deposition and invasive invertebrate herbivores on ecosystem processes, specifically the accumulation of soil carbon (C). We used a N-deposition crossed invasive stem boring weevil experiment on the developing soils of Mount St. Helens to answer our question.
We hypothesized that plots with N addition and weevil exclusion would have the highest soil C from increased plant growth and litter. Weevil exclusion will increase soil organic matter (SOM) and microbial activity increasing C. In plots with weevils and N soil C will be greater than plots without N addition because of high litter fall and frass addition. However, without N addition plant growth will be reduced, especially roots and their exudates which are a primary source of C.
We collected soils from each of our 36 treatment plots and measured soil C and N using an elemental analyzer. Soil C was 20% greater where herbivores were excluded regardless of N addition treatment. Soil C was 30% greater in our east plots compared to our west plots. This may be due to different plant assemblages at each site, slope, aspect, or elevation. Soil C was not significantly different between N treatments suggesting that in early developing systems N might not have an effect in the first years of soil development. However, a single insect herbivore can greatly reduce the rate of SOM accumulation, and that this in turn will slow down colonization by plants that require greater SOM.
About the Presenters
Shawn Preston
Shawn Preston is a graduating senior in the School of Environment and is an undergraduate researcher in the Bishop Disturbance Ecology Lab at Washington State University Vancouver. His research focuses on anthropogenic nitrogen deposition and soils on Mount St. Helens under the School of Biological Sciences. He will be pursuing a graduate degree in Geology at San Jose State University.
Rebecca Evans
Rebecca Evans is a second year PhD student in the Bishop Disturbance Ecology Lab at WSU-Vancouver. She completed her MS at WSU-Pullman where she investigated the effects of an invertebrate herbivore and its plant host species, Lupinus lepidus (prairie lupine), on soil carbon and nitrogen dynamics and the soil microbial community. She is continuing her work on Mount St. Helens, researching the dynamics of plant-microbial relations on soil carbon storage and how invasive herbivores and anthropogenic nitrogen deposition affect soil development and soil carbon.