Invasive species are a serious threat to ecosystems across the globe. Their effect on the community they invade can be drastic, altering site hydrology or stand structure, even causing the extinction of native species. This study focuses on the invasive grass Microstegium vimineum (Mivi), which is prevalent throughout the US East coast. Soils where Mivi is present have been shown to have altered nitrogen (N) dynamics and microbial community structure. However, it is unknown to what extend Mivi is causing these changes or is responding to natural variability. We collected individuals of native species as well as Mivi from a restored wetland and transplanted them, along with the soils they were growing in, to a greenhouse for one growing season. After this period, we sampled soils for microbial biomass (SIR), N mineralization and denitrification (DEA). We also made leachates from the leaves of each sampled species and incubated soils from each species with leachates in a full-factorial design. After a two week incubation period, we measured the same suite of soil characteristics. The goals of this study were to 1) examine species-specific soil processes and 2) determine the effects of Mivi leachates on microbial biomass and N transformations.
At the end of the growing season, there were significant differences between microbial biomass in soils grown with different species. In particular, Mivi soils had significantly elevated microbial biomass (p<0.00001), as measured by SIR. Whether or not this biomass increase is a result of a positive-feedback mechanism should be further investigated. After subsequent incubation with leaf leachate, there were again, significant difference between microbial biomass of the different species’ soil pools (p<0.00001). Post-hoc tests reveal Mivi soils to have significantly (p<0.00001) higher microbial biomass as compared to the other soil pools. This is similar to the trend shown in the species-specific analyses. There does not appear to be any significant leachate effect on microbial biomass. However, there may be leachate effects on N-mineralization or denitrification (analysis currently underway). Such effects would suggest a functional change in the microbe community caused by the presence of Mivi. Our analyses completed to date suggest that Mivi is capable of inducing changes in soil functioning, but the precise mechanism of this effect still needs to be elucidated.