Grass invasion differentially affects carbon cycling across an urban-rural gradient in Southern Appalachian forests

Background/Question/Methods

There is considerable evidence that land use change facilitates exotic plant invasions by increasing introduction rates and creating favorable microhabitats for exotic plants through disturbance. Much less is known about how land use affects the impacts of invaders once they are established. Land use can lead to profound changes in abiotic and biotic conditions, which may alter invader fitness or plant-soil feedbacks. Such changes could increase or decrease the effects of invaders on ecosystem processes. We examine how the ecosystem-level impacts of an aggressive understory invader, Microstegium vimineum, vary in forests spanning an urban-rural gradient in western North Carolina. We established paired invaded-uninvaded plots in forests within an urban, rural, or forested matrix. Within each plot, we deployed litterbags and collected soil to resolve C pools into microbial biomass, mineralizable, root biomass, particulate organic, mineral-associated, and total organic C.

Results/Conclusions

Preliminary results indicate that land use constrains the effects of invasion on litter decomposition. Litter decomposition rates, while higher in invaded than uninvaded plots within a given land-use matrix, are consistently highest within a forested matrix and lowest within in an urban matrix. Similarly, the magnitude of impacts on SOC pools depends on land use context. Although M. vimineum biomass was highest within the urban matrix, invasion had less severe impacts in forests within an urban rather than forested or rural matrix. Invasion reduced soil microbial biomass C by 41 % (52.4 ± 16.5 µg C g soil^-1; mean ± standard error) at sites within a forested matrix compared to 23% (25.5 ± 11.9 µg C g soil^-1) at sites within an urban matrix. These findings suggest that the land use influences invader impacts by altering plant-soil feedbacks. Future studies will address the mechanisms by which land use regulates invader impacts. This work emphasizes the importance of considering spatial context when studying the impacts of biological invasion.