Invasive plant-derived dissolved organic matter alters microbial communities and carbon cycling in soils

Plant invaders often exhibit substantially higher productivity than the communities they replace. However, little is known about interactions among invaders and microbial decomposers responsible for converting organic nutrients into plant-available forms to fuel this productivity. We performed two laboratory incubations with soil and plant material collected from five-year-old experimental plantings to assess if four grassland invaders (Bromus tectorum, Centaurea stoebe, Euphorbia esula and Potentilla recta) or native plant mixtures (including Pseudoroegneria spicata and Penstemon strictus) changed microbial community composition and function (experiment 1), and if plant-derived dissolved organic matter (DOM) contributed to these changes (experiment 2). We measured respiration responses throughout the 39-day incubations and assessed soil bacterial communities with 16S rRNA high-throughput sequencing at 0 and 48 h. Overall, we found bacterial community composition and function differed among plant communities. Two invaders in particular, B. tectorum and E. esula, generated dissimilar DOM with corresponding differences in bacterial composition and function. Soil bacteria accustomed to B. tectorum DOM (high carbon to nitrogen, C:N) harbored more oligotrophs and generated slow but large cumulative responses to a resource pulse. By contrast, soil bacteria accustomed to E. esula DOM (low C:N) harbored more copiotrophs and generated quicker respiration responses. Finally, we found a single pulse of invader-derived DOM shifted bacterial composition in soil associated with native plants. Our findings indicate invaders can differ substantially in interactions with microbial decomposers and these differences are, at least in part, driven by differences in DOM. While increased productivity and accelerated nutrient cycling may be common across invaders, our findings indicate that the underlying mechanisms driving these increases may be specific to each invader.