Plants that can uptake extraordinary amounts of heavy metals, or hyperaccumulators, are being developed for use in phytoremediation of contaminated soils. While the technique is economical and less intrusive than traditional methods, it may have unpredicted ecological impacts on the native community around the remediation site. Thlaspi caerulescens (Brassicaceae) is a cadmium (Cd) and zinc (Zn) hyperaccumulator that is under development for Cd remediation. A demographic study of T. caerulescens experimentally planted at abandoned mine sites in southwest Colorado is underway to compare the performance of plants when planted on contaminated and adjacent, non-contaminated soils. Results from this study would have direct implications for whether populations of this non-native plant introduced for remediation may establish outside of its intended areas. Experimental plots established at the end of the 2006 growing season at three mine sites have been monitored for one growing season. Germination rate, over-winter mortality, and first-year growth (measured as the percentage of plants that graduated to a five-leaf size class in fall 2007) are tested for the effects of site, location (on tailings, adjacent to tailings border, 20m from border), and native vegetation removal treatment.
Results/Conclusions
After the first year, performance of T. caerulescens across the different locations appears to be site-specific. Germination is highest at the tailings at Woods site, but lowest at the tailings for Copper and Cinnamon sites. Overwinter mortality is lowest at the tailings at both Woods and Cinnamon, and intermediate at Copper. First-year growth is not different between sites, and is highest at the tailings. Thus there is evidence that T. caerulescens performs best on the high-metal tailings at my three study sites. The vegetation treatment does not affect germination or winter survivorship. However, first-year growth at all sites is higher in plots with natural vegetation than in removal plots. Thus, at this initial stage, T. caerulescens plants are facilitated by the native vegetation around the contaminated sites. Plant performance can be explained in part by the soil characteristics of the sites. Germination rate is negatively correlated with the total and the plant-available fractions of Cd and Zn in the soil. Interestingly, winter mortality and first-year growth are both positively correlated with soil pH, which ranged from 4.37 to 5.59 across the study sites and locations. First-year growth is also positively correlated with total Zn in the soil, which is consistent with other studies that have demonstrated a Zn requirement in this species.
