Nitrate boosts arsenic accumulation in hyperaccumulator Pteris vittata by coupling nitrogen assimilation with arsenic...

Nitrogen is a critical macronutrient for plant growth including As-hyperaccumulator Pteris vittata. Being common N fertilizers, both NO₃^⁻ and NH₄⁺ enhance As accumulation in P. vittata, but the underlying mechanisms remain unclear. Based on 0.2-strength Hoagland nutrient solution (0.2X HNS, NO₃^⁻/NH₄⁺ = 2.8 mM/0.2 mM), we investigated the impacts of 3.0 mM NO₃^⁻ or NH₄⁺ by growing P. vittata in sand-vermiculite culture for 7 weeks under 50 µM As exposure. Besides plant growth and nutrient uptake, we determined As speciation (arsenate-AsV and arsenite-AsIII), N assimilation and As-metabolism gene expression in P. vittata. Though 0.2X HNS control produced greater plant biomass, NO₃^⁻ and NH₄⁺ treatments increased frond As and P contents by 89-113 and 39-76%. While NO₃^⁻ enhanced N assimilation via nitrate reductase, glutamine synthetase, and free amino acids by 61-157%, 24-65%, and 1.6-5.7 fold, the corresponding increases for NH₄⁺ treatment were 28-125%, 23%, and 2.8-fold. Although both NH₄⁺ and NO₃^⁻ promoted greater As/P uptake and translocation associated with 1.3-2.4 fold upregulation of P-transporters PvPht1;2/1;4 and AsIII-antiporter PvACR3;1, NO₃^⁻ showed greater arsenate reduction and detoxification via 1.4-2.1 fold upregulation of AsV-reductase PvHAC1 and AsIII-antiporters PvACR3/3;2. Overall, NO₃^⁻ is more effective than NH₄⁺ in enhancing As accumulation in P. vittata, which is related to improved N assimilation and As metabolism. This study suggests potential application of NO₃^⁻ to improve phytoremediation of As-contaminated sites based on P. vittata.