Sparingly-Soluble Phosphate Rock Induced Significant Plant Growth and Arsenic Uptake by Pteris vittata from Three Contaminated Soils

Abstract

We evaluated the ability of As-hyperaccumulator Pteris vittata (PV) to remove As from As-contaminated soils over five harvests in 2.5 years in raised beds (162 kg soil/bed). We tested the hypothesis that a P-limiting environment would enhance PV growth and As uptake owing its unique ability to uptake P under As-rich environment. In Dec. 2009, PV was transplanted to three As-contaminated soils (pH of 5.5-7.2) containing 25-129 mg kg(-1) As, which was amended with sparingly-soluble phosphate rock (PR-soil) or soluble P fertilizer (P-soil). During the 2.5-year, PV obtained sufficient P (1882 vs 2225 mg kg(-1)) from PR-soils, with increased root biomass (33%) and root exudation (53%) compared to P-soils. In addition, its frond biomass increased by 20% consecutively with each harvest (six month interval) from 18 to 36 g plant(-1). Its frond biomass in PR-soils (52.2 g plant(-1) year(-1) or ∼12 mt ha(-1) year(-1)) averaged 39% more than that in P-soils. To our knowledge, this represented the largest PV frond biomass reported, demonstrating the unique ability of PV in using insoluble P from PR in alkaline soils. In addition to biomass increase, PV from PR-soils had ∼1.5 times more As in fronds (2540, 780, and 920 mg kg(-1)) than those from P-soils (1740, 570, and 400 mg kg(-1)), with soils containing 129, 25, and 30 mg kg(-1) As, respectively. The low available P in PR-soils induced substantial plant growth and As uptake by PV. This translated into significantly more As removal from soil, averaging 48% reduction in PR-soils and 36% in P-soils in 2.5 years. With multiple harvests and PR amendments, our results showed As removal by PV from contaminated soils was ∼7 times faster than published studies.

Arsenic: behavior in the environment, plant uptake mechanisms and human health risks

“…As in the case of water, soil contamination by As and its translocation to plants also represents a risk to ecology and human health through the consumption of vegetables, and it can also compromise agricultural productivity and the sustainability of ecosystems Ma, 2013).…”

“…Tolerant species usually have roots with large biomass, which are able to adsorb, precipitate, and accumulate the element in their root system, without translocating it to their shoot system. Although the contaminants are not removed from the site, phytostabilization allows reducing the risk of erosion and the leaching of pollutants, preventing groundwater phytotoxicity Ma, 2013;De Oliveira et al, 2014). On the other hand, species unable to tolerate or hyperaccumulate As, such as Acácia mangium and Mimosa caesalpiniaefolia (Cipriani et al, 2013), may experience phytotoxicity, affecting their development and causing death.…”

“…However, phytoextraction of the labile fraction can be reduced according to the species employed in the recovery program (Danh et al, 2014). In a study with P. vittata, Lessl and Ma (2013) reported a 42% reduction in the phytoavailability and bioaccessibility of As after 30 months of cultivation. As removal in the second year of cultivation was higher than in the first year, which emphasizes the potential of P. vittata for phytoextraction of As in the long term.…”

“…Higher levels of As in the root system compared with the aerial part is a characteristic of species with phytoremediation potential. As accumulation in the roots is a strategy to mitigate the toxic effects of the element in organs where physiological processes prevail, such as the leaves Ma, 2013).…”

“…Hyperaccumulator plants accumulate more phosphorus (P) in the roots and more As in the shoots, given the competitive absorption. This mechanism is adopted to reduce the toxic effects of As and mitigate its metabolic interference in the plant Ma, 2013).…”