Ecosystems invaded by exotic plants often exhibit substantially higher plant productivity, soil nutrients, and decomposition rates than the native communities they replace. Given that plant growth is often nutrient limited and decomposition liberates nutrients, we wanted to explore if litter quality differed among invaders and if these differences resulted in predictable shifts in the soil microbial community. Litter influences the microbial community as it decomposes on the soil surface and via pulses of dissolved organic matter (DOM) generated during rainstorms and snowmelt. Here we investigated whether DOM of four common intermountain grassland invaders (Bromus tectorum, Euphorbia esula, Centaurea stoebe, Potentilla recta) and two natives (Pseudoroegneria spicata, Penstemon strictus) differed in the amount and quality of carbon supplied to the soil, and if DOM additions elicited varied responses from the microbial communities.
We used soils and biomass collected from established plots of invader monocultures or native plant mixtures in a 39-day laboratory incubation and periodically measured CO2 efflux to answer the following questions: (1) Does a native-plant-trained microbial community respond to a single addition of invader DOM? (2) Is five years of training by invader monocultures enough time to alter the responses of associated microbial communities to a common DOM? (3) Are responses invader-specific and related to litter quality?
Results/Conclusions
DOM varied in both quantity and quality of carbon, and these differences elicited varied responses by a native-plant-trained microbial community. Euphorbia esula DOM had the lowest C:N ratio and generated a rapid response, whereas B. tectorum had highest C:N ratio and generated a modest initial response that increased through time. When invader-monoculture-trained microbial communities were exposed to a single DOM, the E. esula community mineralized carbon rapidly, whereas P. spicata and B. tectorum communities utilized carbon more slowly, typical of copiotrophic and oligotrophic responses, respectively.
Our results indicate that microbial communities diverge functionally, and in species-specific ways, following invasions. Differences in litter quality and resulting microbial community shifts may contribute to invasion soil legacies and influence restoration success. Thus, while successful invaders share many traits and are capable of outcompeting and replacing native plants, they may differ significantly in terms of litter quality and influence on microbial communities. Compositional differences of the soil microbial communities are being investigated and will be presented.