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

Exotic invasive plants increase productivity, abundance of ammonia-oxidizing bacteria and nitrogen availability in intermountain grasslands

EA SPE BIOME CT3International audienceExotic plant invasion is often associated with dramatic increases in above-ground net primary productivity and soil nitrogen. However, most evidence for these increases comes from correlative studies of single species, leaving open the question of whether invasive plants drive these processes and whether they are consistent among invaders. * We combined field surveys and measurements within experimental plantings to examine how plant productivity, soil nitrogen and the abundance of ammonia-oxidizing bacteria (AOB) change in response to invasions by four exotic species. * The relationship between plant productivity and soil nitrate differed among native and invasive species, suggesting a fundamental disparity in the effects of natives and invaders on ecosystem processes. In field surveys, dense patches of all invasive species had higher abundances of AOB than native-dominated sites. Three of the four invasive species had higher productivity, soil nitrate concentrations and rates of potential nitrification as compared to nearby native-dominated communities. In our experimental plantings, we found that two invasive species drove increases in soil nitrate and one invader caused increased productivity after a single season. * Synthesis. Our results highlight the importance of the N cycling soil microbial community in how exotic invasive plants alter ecosystem function and show that shifts in function can occur rapidly

Inhibitory effects of Eucalyptus globulus on understorey plant growth and species richness are greater in non-native regions

Aim: We studied the novel weapons hypothesis in the context of the broadly distributed tree species Eucalyptus globulus. We evaluated the hypothesis that this Australian species would produce stronger inhibitory effects on species from its non‐native range than on species from its native range. Location: We worked in four countries where this species is exotic (U.S.A., Chile, India, Portugal) and one country where it is native (Australia). Time period: 2009–2012. Major taxa studied: Plants. Methods: We compared species composition, richness and height of plant communities in 20 paired plots underneath E. globulus individuals and open areas in two sites within its native range and each non‐native region. We also compared effects of litter leachates of E. globulus on root growth of seedlings in species from Australia, Chile, the U.S.A. and India. Results: In all sites and countries, the plant community under E. globulus canopies had lower species richness than did the plant community in open areas. However, the reduction was much greater in the non‐native ranges: species richness declined by an average of 51% in the eight non‐native sites versus 8% in the two native Australian sites. The root growth of 15 out of 21 species from the non‐native range were highly suppressed by E. globulus litter leachates, whereas the effect of litter leachate varied from facilitation to suppression for six species native to Australia. The mean reduction in root growth for Australian plants was significantly lower than for plants from the U.S.A., Chile and India. Main conclusions: Our results show biogeographical differences in the impact of an exotic species on understorey plant communities. Consistent with the novel weapons hypothesis, our findings suggest that different adaptations of species from the native and non‐native ranges to biochemical compounds produced by an exotic species may play a role in these biogeographical differences