Quantifying the trade-offs of native and non-native heavy metal hyperaccumulating weeds (Plantago spp.) and their influence on rhizospheric soil microarthropod communities in contaminated sites in Baltimore

Background/Question/Methods

Cities like Baltimore, MD are highly contaminated with heavy metals like lead and chromium, however some weedy plant species can safely store these heavy metals in their aboveground tissues at very high concentrations, called hyperaccumulation. Uptake of heavy metals by these plants also alters rhizospheric soil (i.e. pH, metal bioavailability, etc.), and influences soil microarthropod diversity and/or abundance. We focus here on Plantago spp. (plantains; Plantaginaceae) which are globally common and known hyperaccumulators. We compare metal content and growth traits in non-native species P. lanceolata and P. major, native P. rugelii, and control samples (i.e. no hyperaccumulators) from the field, characterize soil microarthropod abundance, quantify heavy metal content using inductively coupled plasma mass spectrometry (ICP-MS), and compare this to legacy heavy metal data from 2006. We predict that 1) rosette diameter, leaf number, and flowering stem number will decrease in highly contaminated sites due to trade-offs between growth and tissue metal content, while rosette height will increase, which is common in hyperaccumulating plants, and 2) soil microarthropod abundance will be greater in Plantago rhizospheres than in control rhizospheres, as the Plantago spp. will have extracted much of the heavy metals from their local soils producing a “cleaner” environment.

Results/Conclusions

We find that of the growth trait responses (rosette diameter, rosette height, leaf number, and flowering stem number) are species dependent. Growth traits of P. lanceolata are not significant with degree of heavy metal contamination (p>0.05), whereas in P. major and P. rugelii, leaf number (ANOVA: p_major=0.018; p_rugelii=0.037) and flowering stem number (ANOVA: p_major<0.001; p_rugelii=0.0151) differ significantly between historically high and low levels of contamination. However, we find that while P. lanceolata did not differ in terms of growth traits between contamination levels, its rhizosphere contained significantly more soil microarthropods than P. major and P. rugelii (p_ANOVA=0.0125), as well as when compared to control soils (p_ANOVA=0.0001). It is likely that P. lanceolata is providing a locally reduced, “cleaner” rhizosphere environment than P. major and P. rugelii. Further testing of plant tissue and soil metal content is underway to quantify heavy metal content.