Performance of native perennials in brownfield soil conditions: Solidago canadensis and Eupatorium serotinum match dominant invasive Artemisia vulgaris
Plants growing in brownfields have to cope with stressful conditions including high levels of contaminants. Previous vegetation surveys of old fields and brownfields showed that native species richness is similar between the two site types but that native species abundance is lower in brownfields. I conducted a greenhouse experiment with perennial Asteraceae species to test the hypothesis that certain characteristics of brownfield soil negatively impact the growth of dominant natives more than they affect the dominant non-natives. The species studied were natives Solidago canadensis and Eupatorium serotinum, and non-natives Cirsium arvense and Artemisia vulgaris. Young plants of each species were collected from multiple old fields. Three experimental treatments mimicked salient brownfield conditions of altered soil texture, low levels of nutrients, and high concentrations of heavy metals. Soil texture was altered by mixing gravel into topsoil, low nutrients were achieved by adding nutrients to all other treatments including the control of otherwise unaltered topsoil, and high metal levels were created by an addition of soluble salts of chromium, lead, and zinc. A combination treatment of gravel, low nutrients, and metals was also included. The plants were grown for four months and then were harvested for above- and belowground biomass.
Species identity, treatment, and species-treatment interaction significantly influenced the variance of above- and belowground biomass. Artemisia and Solidago responded similarly across all treatments, with highest biomass in the control treatment, a slight reduction in the gravel treatment, and a larger reduction in the metal treatment (39% lower for Artemisia, 33% lower for Solidago). Eupatorium biomass peaked in the altered texture treatment, but otherwise performed similarly to Artemisia and Solidago. All three of these species produced on average the lowest biomass under nutrient stress. Cirsium did not grow well, with final dry biomass lower than the initial fresh weights regardless of soil treatment. Since the native Solidago and Eupatorium performed similarly in brownfield soil conditions to the non-native Artemisia, there is no support for the hypothesis that a non-native species is better adapted to these brownfield conditions than natives. Lower percent cover of natives in brownfields found in vegetation surveys may be due to priority effects, competition, propagule pressure, or effects on growth and reproduction not measurable in one season. These results suggest that native Solidago and Eupatorium can grow in brownfield soils as well as invasive Artemisia, and could possibly be the dominant species in a brownfield if established first.