Urban weedy plantains (Plantago spp.) do not hyperaccumulate heavy metals nor shelter their soil microarthropod communities from these metals

Heavy metal hyperaccumulation by plants is a powerful tool in phytoremediation, where plants store heavy metals in large amounts in their aboveground tissue. Plant species in the Plantago genus exhibit this phenomenon, and their commonness in metropolitan centers around the world make them strong candidates for use in cities. Additionally, alteration of soil conditions by these plants can have cascading consequences on their soil microarthropod communities, which are strong bioindicators of soil health. To this end, we investigated the hyperaccumulation ability of two plantain species, Plantago lanceolata (non-native to North America) and Plantago rugelii (native to North America), and their soil microarthropod communities from field-collected specimens in Baltimore, MD, USA, which has an extensively documented legacy of heavy metal contamination. Notably, this is the first study to assess the influence of plant hyperaccumulation on soil microarthropod abundance and diversity using soil health bioindication metrics. First, we found that all sites sampled in Baltimore, MD exceed US governmental soil limits for As and Fe. Second, neither Plantago spp. hyperaccumulates any heavy metal in standard heavy metal screenings, though both species show signs of sequestration of some metals in their roots (i.e., phytoexclusion). Additionally, while native P. rugelii did not hyperaccumulate metals in this study, the relatively high translocation factor (TF or root: shoot) suggests it may have the capacity for it. We also found that soil microarthropod abundance was significantly greater in P. lanceolata rhizospheres (p < 0.05), but bioindication of soil health (acari: collembola) was dependent on a combination of plant species identity and contamination level. Lastly, we found that soil microarthropod diversity was significantly affected by Al and As concentration.