The effects of invasive European Buckthorn (Rhamnus cathartica) on soil microbial community composition

European Buckthorn (Rhamnus cathartica) is an invasive shrub that was introduced to North America in the 1800s. Comparisons of buckthorn-invaded and native-dominated woodlands suggest that buckthorn might increase soil nitrogen and carbon by stimulating rapid decomposition of litter. Because decomposition and nitrogen cycling are microbial processes, I hypothesize that buckthorn invasion changes the community composition of soil microbes, and these changes should increase with increasing severity of buckthorn invasion. To generalize the effects of buckthorn invasion, I looked at soils collected from 97 pairs of buckthorn-invaded and uninvaded reference sites across 15 remnant woodlands in an approximately 5,500-km2 region of the Chicago area. The severity of the buckthorn-invaded sites was scored based on information about the age, basal area, canopy coverage, and sapling density of buckthorn. I used automated ribosomal intergenic spacer analysis (ARISA) and quantitative PCR (qPCR) to characterize the invaded vs. reference site differences of soil microbial community composition and the abundance of nitrogen-cycling functional groups. I used linear regression to test the hypothesis that invaded vs. reference site differences in microbial communities and nitrogen-cycling functional groups increase with increasing severity of buckthorn invasion, and I used multivariate ordination to look at general patterns of community composition across these sites. I found that buckthorn invasion is related to small but significant shifts in microbial community composition across this area. Invasion severity significantly increased differences in bacterial communities between invaded and reference sites, and this increasing effect of buckthorn was most strongly related to the density of buckthorn saplings in at the invaded site. No such trends were detected for soil fungi. However, the projection of regression lines to zero invasion severity (i.e. no buckthorn) indicated that some differences in soil microbial communities might pre-date the buckthorn invasion. Buckthorn-invaded sites had higher abundance of Archaeal amoA (ammonia oxidizer) genes than uninvaded sites, but there were no significant differences detected in any of the other nitrogen-cycling functional groups. However, regression analysis suggested that the abundance of archaeal nitrifiers was not related to invasion severity, and the differences between invaded and reference sites may pre-date buckthorn invasion. Overall, my results suggest that the direct effect of the buckthorn invasion on microbial communities is small relative to other sources of spatial and environmental variation, and that observed microbial differences between buckthorn-invaded and uninvaded soils reflects environmental variation that pre-dates buckthorn invasion.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Natural Res & Env Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2013

Author dc:creator

• Lin, Huei-Ming

Contributors dc:contributor

• Yannarell, Anthony C.

• European Buckthorn
• Rhamnus cathartica
• invasive species
• belowground communities
• bacterial community
• fungal community
• automated ribosomal intergenic spacer analysis (ARISA)
• quantitative Polymerase Chain Reaction (qPCR)
• Nitrogen cycle
• nitrifier

Statement dc:rights

• Copyright 2013 Huei-Ming Lin

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/44170

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/44170