Effects of the Invasive Shrub Frangula alnus on Soil Microbial Communities and Biogeochemical Processes

Abstract

The objective of this research was to determine the impacts of the invasive plant Frangula alnus, glossy buckthorn, on soil properties and microbial communities. Two studies were completed to achieve this objective. The first study examined the short-term impacts of F. alnus litter on soil properties and microorganims. In situ soil rings received the following aqueous treatments: deionized water, dextrose, cellulose, Quercus alba leaf extract, and F. alnus leaf extract (n = 7) and were sampled 1, 2, and 4 weeks after additions were made. In weeks 1 and 2, soil treated with F. alnus had higher total extractable N (NO3- + NH4+; TEN) than other treatments, which was likely due to enhanced N mineralization. In addition, changes to the microbial biomass C (MBC) to N (MBN) ratio in the F. alnus-treated soil indicated that microbial function had been altered. Overall, results suggest that F. alnus leaf litter has the capacity to alter soil properties and microbial function by stimulating N mineralization. The second study compared microbial communities and biogeochemical properties of soil at sites with F. alnus to non-invaded sites. Paired invaded/non-invaded sites (n = 11), including high (n = 6) and low (n = 5) density invasions, were sampled in spring, summer and fall of 2013. Paired t-tests revealed higher net N mineralization rates in invaded sites than non-invaded sites in summer, and in high density invaded sites than non-invaded sites during all sampling seasons. There was not, however, a corresponding increase in TEN at invaded sites. In addition, no differences between invaded and non-invaded sites were observed for soil C pools, MBC, MBC:MBN, and microbial community structure as assessed by terminal restriction fragment length polymorphisms. Overall, results suggest that F. alnus alters N cycling but has little impact on soil C pools.