Individual strategies of growth on invasive and native prairie species on different nutrients environments

Prairie restoration requires the understanding of mechanisms that allow native species to cope with enriched soils.  Biomass allocation might differ between native and invasive prairie species since native species are adapted to nutrient poor soils. We investigated allocation to roots, shoots and leaves of invasive and native prairie forbs: Solidago rigida, Asclepias sullivantii, Solidago canadensis, and Asclepias syriaca to measure responses to nitrogen and calcium.  In a greenhouse study we grew 400 plants at four combinations of these nutrients (H_N H_Ca , H_N L_Ca, L_N H_ca, L_N L_ca) for seven weeks.  Each week, we harvested five plants per treatment and we determined height, leaf area, and dry biomass of roots, shoots, and leaves.  High nitrogen significantly increased plant size, root and shoot biomass for all species (size: p<0.001; roots: p<0.001; shoots: p<0.001). Root:shoot ratio was also sensitive to nitrogen level (p<0.001 for all species) with increased allocation to roots when nitrogen was low. This ratio remained constant over all harvests for invasive species, but not natives, suggesting plasticity for this trait for invasives.  With the exception of A. sullivantii, specific leaf area (SLA) did not respond to nutrient treatments; A. sullivantii SLA was highest at low nitrogen.  Leaf Area Ratio (LAR) responded to nutrient concentration for the Solidagos pair but not for the Asclepias pair.  Taken together, these results reveal increased plasticity as a mechanism that confers competitive superiority of invasives over natives even at reduced nitrogen levels. Therefore, soil management should be combined with other strategies in prairie restoration.