Abstract
Soil arsenic heterogeneity complicates our understanding of phytoextraction rates during arsenic phytoextraction with Pteris vittata, including in response to rate stimulation with nutrient treatments. In a 58-week arsenic phytoextraction field study, we determined the effects of soil arsenic concentrations, fertilizer application, and mycorrhizal fungi inoculation on P. vittata arsenic uptake rates, soil arsenic depletion, and arsenic soil–plant mass balances. Initial soil arsenic concentrations were positively correlated with arsenic uptake rates. Soil inoculation with mycorrhizal fungus Funneliformis mosseae led to 1.5–2 times higher fern aboveground biomass. Across all treatments, ferns accumulated a mean of 3.6% of the initial soil arsenic, and mean soil arsenic concentrations decreased by up to 44%. At depths of 0–10 cm, arsenic accumulation in P. vittata matched soil arsenic depletion. However, at depths of 0–20 cm, fern arsenic accumulation could not account for 61.5% of the soil arsenic depletion, suggesting that the missing arsenic could have been lost to leaching. A higher fraction of arsenic (III) (12.8–71.5%) in the rhizosphere compared to bulk soils suggests that the rhizosphere is a distinct geochemical environment featuring processes that could solubilize arsenic. To our knowledge, this is the first mass balance relating arsenic accumulation in P. vittata to significant decreases in soil arsenic concentrations under field conditions.
Highlights
Anthropogenic activities and geogenic processes lead to elevated concentrations of arsenic in soil, soil porewater, and plant tissue, increasing human exposure to this carcinogen [1,2,3,4,5,6,7]
Our report of P. vittata arsenic uptake on a continuum of soil arsenic concentrations fill in gaps in previous reports of higher P. vittata biomass in the presence of low to moderate soil arsenic concentrations compared to arsenic-free soils [76]
We found no treatment effect on fern arsenic accumulation and soil arsenic depletion, contrary to observations that compost and phosphorus soil treatments can lead to arsenic desorption and increase arsenic concentrations in porewater [27,47] and potentially increase arsenic uptake in the fern and/or arsenic leaching from soil
Summary
Anthropogenic activities and geogenic processes lead to elevated concentrations of arsenic in soil, soil porewater, and plant tissue, increasing human exposure to this carcinogen [1,2,3,4,5,6,7]. The chemical form of arsenic controls its solubility, bioavailability, and toxicity [9]. In soils and aqueous environments, arsenic occurs mainly as arsenic(V) (H2 AsO4 − and HAsO4 2− in a pH of range 2–11) in oxidizing conditions, and arsenic(III) (H3 AsO3 for pH below 9) [10] in moderately reducing conditions. Both arsenic(V) and arsenic(III) can be water-soluble in soils depending on the redox conditions and pH [10,11].
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