Understanding the factors that determine invasive species success continues to be important because of the demonstrated negative economic and ecological impacts of invasive species. The intentional introduction of metal-hyperaccumulating plants for phyotremediation creates an excellent opportunity to test the effects of interactions between biotic and abiotic factors on the establishment and success of introduced plants. Metal hyperaccumulating plants can uptake extraordinarily high concentrations of heavy metals into shoot tissues, and may be used to remediate soils that are contaminated by heavy metals as an alternative to costly and intrusive methods such as landfilling. I experimentally introduced Noccaea (formerly Thlaspi) caerulescens, a Zn and Cd-hyperaccumulator, to three study sites with contaminated silver mine tailings, near the Rocky Mountain Biological Laboratory in Gothic, Colorado. I performed a series of field and greenhouse studies to examine how biotic and abiotic factors contribute its potential establishment at non-native sites.
Inter- and Intra-specific competition
The major factors determining whether hyperaccumulators would become invasive at introduced sites include the suitability of uncontaminated substrate for growth and reproduction of the plant, and the strength of biotic resistance against plants grown on that substrate. This experiment specifically tested the competition component of biotic resistance. I tested whether Noccaea caerulescens would compete with a native congener, Noccaea fendleri (formerly Thlaspi montanum var. montanum), which occurs at my study sites. Using field-collected substrate and a response surface design in this greenhouse experiment, I estimated the competition coefficient for each species. A greater effect of interspecific competition from N. caerulescens on N. fendleri would indicate an ability for the non-native species to outcompete the native, and thus higher potential for establishment.
Plant-herbivore interactions
This experiment focused on the natural enemy aspect of biotic resistance, specifically herbivory from native herbivores. I used a Lepidopteran herbivore, Pieris napi, from my study sites in a feeding choice trial experiment. I asked whether P. napi larvae demonstrate a preference between their native food plant N. fendleri and the non-native N. caerulescens, and whether this preference depends upon the leaf Cd and Zn concentrations. Metal concentration has previously been shown to deter herbivory, but whether this affects herbivore preference between native and non-native plants has not been examined.
Che-Castaldo, J.P. and D.W. Inouye. 2015. Interspecific competition between a non-native metal-hyperaccumulating plant (Noccaea caerulescens, Brassicaceae) and a native congener across a soil metal gradient. Australian Journal of Botany (special issue on Ultramafic Ecosystems) 63(2):141–151. pdf
Che-Castaldo, J.P. and D.W. Inouye. 2014. Field germination and survival of experimentally introduced metal hyperaccumulator Noccaea caerulescens (Brassicaceae) across a soil metal gradient. American Midland Naturalist 171(2): 229-245. pdf
Che-Castaldo, J.P. and D.W. Inouye. 2011. Foliar metal concentrations affect native herbivore preference between an introduced metal hyperaccumulating plant and a native congener (Doctoral dissertation). retrieve from https://drum.lib.umd.edu/handle/1903/11696.
Che-Castaldo, J.P. and D.W. Inouye. 2015. Interspecific competition between a non-native metal-hyperaccumulating plant (Noccaea caerulescens, Brassicaceae) and a native congener across a soil metal gradient. Australian Journal of Botany (special issue on Ultramafic Ecosystems) 63(2):141–151. pdf
Che-Castaldo, J.P. and D.W. Inouye. 2014. Field germination and survival of experimentally introduced metal hyperaccumulator Noccaea caerulescens (Brassicaceae) across a soil metal gradient. American Midland Naturalist 171(2): 229-245. pdf
Che-Castaldo, J.P. and D.W. Inouye. 2011. Foliar metal concentrations affect native herbivore preference between an introduced metal hyperaccumulating plant and a native congener (Doctoral dissertation). retrieve from https://drum.lib.umd.edu/handle/1903/11696.