Tue, Aug 03, 2021:On Demand
Background/Question/Methods
Cities like Baltimore, MD are highly contaminated with heavy metals like lead and chromium, however, some weedy plant species can store these metals in their aboveground tissues at very high concentrations, called hyperaccumulation. This physiological phenomenon has been applied to phytoremediation of industrial heavy metal contamination. We focus here on Plantago spp. which are globally common hyperaccumulators found across naturalized to urban systems. Uptake of heavy metals by these plants also alters local rhizopsheric soil (i.e. pH, metal bioavailability, etc.), which influences soil microarthropod diversity and abundance. We compare soil and plant 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 19 grassy road verges and medians across Baltimore. We also characterize soil microarthropod abundance and diversity. We predict that 1) Baltimore soils exceed a biological threshold that facilitates hyperaccumulation in Plantago species. 2) Rosette diameter, leaf number, and flowering stem number will decrease in highly contaminated sites due to heavy metal hyperaccumulation trade-offs, while rosette height will increase. 3) Soil microarthropod abundance will be greater in Plantago rhizospheres than in control rhizospheres, as the Plantago spp. will have “cleaned” the soil by depleting soil heavy metals.
Results/Conclusions All sites exceeded MD Dept. of the Environment (MDE) soil cleanup standards in at least two heavy metals (Al, Cu, Cr, Fe, Pb, or Zn). However, we find that heavy metal hyperaccumulation occurs rarely in Plantago spp. in Baltimore, MD. Only 2 P. rugelii and 1 P. major specimens reach tissue metal content exceeding the hyperaccumulation threshold, and only for Al (>1000ppm), despite 10 of 19 sites exceeding MDE standards. We also find that growth trait responses to metal concentrations is largely species dependent. For example, P. lanceolata rosette diameter and number of leaves are significantly correlated with increasing Al and Fe concentration, but not in either P. major or P. rugelii, while P. rugelii height shows significant correlation with Fe and Pb. Relative to control soils, we find that all three species had significantly greater soil microarthropod abundances (pANOVA=0.0001), where P. lanceolata had the highest abundance (pANOVA=0.0125). It is likely that P. lanceolata is providing a locally reduced, “cleaner” microhabitat environment than P. major and P. rugelii.
Results/Conclusions All sites exceeded MD Dept. of the Environment (MDE) soil cleanup standards in at least two heavy metals (Al, Cu, Cr, Fe, Pb, or Zn). However, we find that heavy metal hyperaccumulation occurs rarely in Plantago spp. in Baltimore, MD. Only 2 P. rugelii and 1 P. major specimens reach tissue metal content exceeding the hyperaccumulation threshold, and only for Al (>1000ppm), despite 10 of 19 sites exceeding MDE standards. We also find that growth trait responses to metal concentrations is largely species dependent. For example, P. lanceolata rosette diameter and number of leaves are significantly correlated with increasing Al and Fe concentration, but not in either P. major or P. rugelii, while P. rugelii height shows significant correlation with Fe and Pb. Relative to control soils, we find that all three species had significantly greater soil microarthropod abundances (pANOVA=0.0001), where P. lanceolata had the highest abundance (pANOVA=0.0125). It is likely that P. lanceolata is providing a locally reduced, “cleaner” microhabitat environment than P. major and P. rugelii.