Allometry and photosynthetic capacity of poplar (Populus deltoides) along a metal contamination gradient in an urban brownfield

The value of urban green space has become an increasingly controversial issue. In particular, development of novel vegetative assemblages on vacant lands may have many formerly unrecognized benefits. However, questions remain regarding the functional impairment of these assemblages due to degraded soils. We investigated the effects of elevated concentrations of soil metals on allometry and photosynthetic capacity of naturally colonized poplars (Populus deltoides Michx.) growing at Liberty State Park, New Jersey. We found that allometries of harvested trees did not differ significantly between the low metal load (LML) and high metal load (HML) sites suggesting that metal contamination did not negatively affect carbon allocation patterns of the target species. Likewise, photosynthetic parameters did not differ significantly between the LML and HML sites, suggesting that soil metal contamination did not negatively affect photosynthetic capacity. However, trees from the LML site were significantly younger for a given size than trees from the HML site. Trees from the medium metal load site (MML) differed significantly in allometry and photosynthetic parameters from the other two sites suggesting other edaphic and ecological factors are a stronger driver for carbon allocation patterns and photosynthetic capacity in these trees. Taken together, this research suggests that sapling establishment and growth may be impaired by heavy metals and that trees in HML sites may incur more maintenance costs than trees in LML sites. However, given enough time, poplars can provide considerable rehabilitation of urban brownfields, particularly those that exhibit soil metal contamination.