Timing of phosphate application affects arsenic phytoextraction by Pteris vittata L. of different ages

Evaluation of Multiple Responses Associated with Arsenic Tolerance and Accumulation in Pteris vittata L. Plants Exposed to High As Concentrations under Hydroponics

Chinese brake fern (Pteris vittata L.) is recognized as an arsenic hyperaccumulating plant. Mechanisms underlying this capability and the associated hypertolerance have been described even if not completely elucidated. In this study, with the aim to expand the knowledge on the matter, an experimental trial was developed to investigate an array of responses, at the morphological, physiological, and biochemical level, in P. vittata plants exposed to high As concentrations in a long-term experiment under hydroponics. Results confirmed the ability of fern plants to both tolerate and accumulate a remarkable amount of As, especially in fronds. Notably, in As-treated plants, a far higher As content was detected in young fronds compared to old fronds, with bioaccumulation (BCF) and translocation (Tf) factors in accordance. At the biochemical level, As treatment affected macro and micronutrient, thiol, and phytochelatin concentrations in fronds of treated plants differently than that of the control. Physiological measurements accounted for a reduction in the photosynthetic activity of As-treated plants in the absence of visual symptoms of damage. Overall, the observed As tolerance and accumulation processes were discussed, evidencing how young fronds developed during As treatment maintain their physiological status while accumulating a high As content. Such indications could be very useful to improve the effective utilization of this plant species for phytofiltration of As-polluted water.

Arsenic removal by As-hyperaccumulator Pteris vittata from two contaminated soils: A 5-year study

The ability of As-hyperaccumulator Pteris vittata to remove As from two contaminated soils (CCA from an As-treated wood facility and DVA from a cattle-dipping vat) over 5 years was investigated for the first time. The goal was to evaluate P. vittata's ability to continuously remove As during 10 harvests and identify how soil As was affected by P. vittata under P-sufficient (P-fertilizer) and P-limiting (phosphate rock) conditions. Sequential extraction was used to determine changes in metal distribution among different soil fractions. The high frond biomass production occurred on the 9th (62.1-63.9 and 35.6-63.5 g plant^-1) and 10th harvest (58.6-60.7 and 51.9-57.1 g plant^-1) for CCA and DVB soils, though frond As concentration decreased. Soil arsenic removal averaged 7-10% per harvest during the 1-6th harvests and was reduced to 0-3% during the 7-10th harvests for DVA and CCA soils. Arsenic from all fractions, excluding the residual fraction, was affected by plant uptake. The largest reduction occurred in the amorphous fraction of CCA-soil at 64-66% (61.2-61.5 to 20.8-21.8 mg kg^-1) and in the crystalline fraction of DVA-soil at 50-86% (2.18-4.35 to 0.61-1.10 mg kg^-1). Soil As concentrations were reduced by 37-47% from 26.7 to 129 to 15.6-16.8 and 68.9-70.1 mg kg^-1 for the DVA and CCA soils, respectively. Our data indicated that P. vittata efficiently solubilized non-labile As under P-limiting conditions without impacting its As depletion.

Intercropping efficiency of four arsenic hyperaccumulator Pteris vittata populations as intercrops with Morus alba

Soils that are slightly or moderately contaminated with arsenic (As) can be safely utilized by intercropping As hyperaccumulator Pteris vittata with cash crops. Introducing hyperaccumulators into crop planting systems results in the alleviation of the adverse effects of As and competition effect for resources. The balance between these two effects determines intercropping efficiency. The effect of using different hyperaccumulator populations on such balance is the focus of this study. Through a tank experiment, four P. vittata populations were compared on the basis of their intercropping efficiencies and physiological and morphological characteristics. The evaluation of the intercropping efficiency of P. vittata was mainly based on the capabilities of the species to promote growth and decrease As concentrations in intercropped Morus alba. Two populations of P. vittata were appropriate for intercropping with M. alba, with the alleviation effect of As harm as the main effect on the intercropping system. These populations showed extensive root overlap with M. alba and efficient uptake of bioavailable As, thus depleting As in the rhizosphere and lowering As risk. After different P. vittata populations were used, varied interspecific interactions were observed. Root overlap and aboveground morphological parameters are the key factors determining intercropping efficiency among P. vittata populations.

Arsenic-phosphorus interactions in the soil-plant-microbe system: Dynamics of uptake, suppression and toxicity to plants

High arsenic (As) concentrations in the soil, water and plant systems can pose a direct health risk to humans and ecosystems. Phosphate (Pi) ions strongly influence As availability in soil, its uptake and toxicity to plants. Better understanding of As(V)-Pi interactions in soils and plants will facilitate a potential remediation strategy for As contaminated soils, reducing As uptake by crop plants and toxicity to human populations via manipulation of soil Pi content. However, the As(V)-Pi interactions in soil-plant systems are complex, leading to contradictory findings among different studies. Therefore, this review investigates the role of soil type, soil properties, minerals, Pi levels in soil and plant, Pi transporters, mycorrhizal association and microbial activities on As-Pi interactions in soils and hydroponics, and uptake by plants, elucidate the key mechanisms, identify key knowledge gaps and recommend new research directions. Although Pi suppresses As uptake by plants in hydroponic systems, in soils it could either increase or decrease As availability and toxicity to plants depending on the soil types, properties and charge characteristics. In soil, As(V) availability is typically increased by the addition of Pi. At the root surface, the Pi transport system has high affinity for Pi over As(V). However, Pi concentration in plant influences the As transport from roots to shoots. Mycorrhizal association may reduce As uptake via a physiological shift to the mycorrhizal uptake pathway, which has a greater affinity for Pi over As(V) than the root epidermal uptake pathway.

Arsenic-induced plant growth of arsenic-hyperaccumulator Pteris vittata: Impact of arsenic and phosphate rock

Phosphate rock (PR) has been shown to promote plant growth and arsenic (As) uptake by As-hyperaccumulator Pteris vittata (PV). However, little is known about its behaviors in agricultural soils. In this study, impact of 50 mg kg(-1) As and/or 1.5% PR amendment on plant As accumulation and growth was investigated by growing PV for 90 d in three agricultural soils. While As amendment significantly increased plant As uptake and substantially promoted PV growth, the opposite was observed with PR amendment. Arsenic amendment increased plant frond As from 16.9-265 to 961-6017 mg kg(-1),whereas PR amendment lowered frond As to 10.2-216 mg kg(-1). The As-induced plant growth stimulation was 69-71%. While PR amendment increased plant Ca and P uptake, As amendment showed opposite results. The PV biomass was highly correlated with plant As at r = 0.82, but with weak correlations with plant Ca or P at r < 0.30. This study confirmed that 1) As significantly promoted PV growth, probably independent of Ca or P uptake, 2) PR amendment didn't enhance plant growth or As uptake by PV in agricultural soils with adequate available P, and 3) PV effluxed arsenite (AsIII) growing in agricultural soils.

Integrated phytobial remediation for sustainable management of arsenic in soil and water

Arsenic (As), cited as the most hazardous substance by the U.S. Agency for Toxic Substance and Disease Registry (ATSDR, 2005), is an ubiquitous metalloid which when ingested for prolonged periods cause extensive health effects leading to ultimate untimely death. Plants and microbes can help mitigate soil and groundwater As problem since they have evolved elaborate detoxification machineries against this toxic metalloid as a result of their coexistence with this since the origin of life on earth. Utilization of the phytoremediation and bioremediation potential of the plants and microbes, respectively, is now regarded as two innovative tools that encompass biology, geology, biotechnology and allied sciences with cutting edge applications for sustainable mitigation of As epidemic. Discovery of As hyperaccumulating plants that uptake and concentrate large amounts of this toxic metalloid in their shoots or roots offered new hope to As phytoremediation, solar power based nature's own green remediation. This review focuses on how phytoremediation and bioremediation can be merged together to form an integrated phytobial remediation which could synergistically achieve the goal of large scale removal of As from soil, sediment and groundwater and overcome the drawbacks of the either processes alone. The review also points to the feasibility of the introduction of transgenic plants and microbes that bring new hope for more efficient treatment of As. The review identifies one critical research gap on the importance of remediation of As contaminated groundwater not only for drinking purpose but also for irrigation purpose and stresses that more research should be conducted on the use of constructed wetland, one of the most suitable areas of application of phytobial remediation. Finally the review has narrowed down on different phytoinvestigation and phytodisposal methods, which constitute the most essential and the most difficult part of pilot scale and field scale applications of phytoremediation programs.

Sparingly-soluble phosphate rock induced significant plant growth and arsenic uptake by Pteris vittata from three contaminated soils

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.

Phytoremediation of arsenic contaminated soil by Pteris vittata L. I. Influence of phosphatic fertilizers and repeated harvests

A greenhouse experiment was conducted to evaluate the effectiveness of diammonium phosphate (DAP), single superphosphate (SSP) and two growing cycles on arsenic removal by Chinese Brake Fern (Pteris vittata L.) from an arsenic contaminated Typic Haplustept of the Indian state of West Bengal. After harvest of Pteris vittata the total, Olsen's extractable and other five soil arsenic fractions were determined. The total biomass yield of P. vittata ranged from 10.7 to 16.2 g pot(-1) in first growing cycle and from 7.53 to 11.57 g pot(-1) in second growing cycle. The frond arsenic concentrations ranged from 990 to 1374 mg kg(-1) in first growing cycle and from 875 to 1371 mg kg(-1) in second growing cycle. DAP was most efficient in enhancing biomass yield, frond and root arsenic concentrations and total arsenic removal from soil. After first growing cycle, P. vittata reduced soil arsenic by 10 to 20%, while after two growing cycles Pteris reduced it by 18 to 34%. Among the different arsenic fractions, Fe-bound arsenic dominated over other fractions. Two successive harvests with DAP as the phosphate fertilizer emerged as the promising management strategy for amelioration of arsenic contaminated soil of West Bengal through phyotoextraction by P. vittata.

Uptake and transport of roxarsone and its metabolites in water spinach as affected by phosphate supply

Roxarsone (ROX) is widely used as a feed additive in intensive animal production. While an animal is fed with ROX, the As compounds in the manure primarily occur as ROX and its metabolites, including arsenate (As[V]), arsenite (As[III]), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA). Animal manure is commonly land applied with phosphorous fertilizers in China. A pot experiment was conducted to investigate the phytoavailability of ROX, As(V), As(III), MMA, and DMA in water spinach (Ipomoea aquatica), with the soil amended with 0, 0.25, 0.50, 1.0, and 2.0 g PO(4)/kg, respectively, plus 2% (w/w manure/soil) chicken manure (CM) bearing ROX and its metabolites. The results indicate that this species of water spinach cannot accumulate ROX and MMA at detectable levels, but As(V), As(III), and DMA were present in all plant samples. Increased phosphorous decreased the shoot As(V) and As(III) in water spinach but did not affect the root As(V). The shoot DMA and root As(III) and DMA were decreased/increased and then increased/decreased by elevated phosphorous. The total phosphorous content (P) in plant tissue did not correlate with the total As or the three As species in tissues. Arsenate, As(III), and DMA were more easily accumulated in the roots, and phosphate considerably inhibited their upward transport. Dimethylarsinic acid had higher transport efficiency than As(V) and As(III), but As(III) was dominant in tissues. Conclusively, phosphate had multiple effects on the accumulation and transport of ROX metabolites, which depended on their levels. However, proper utilization of phosphate fertilizer can decrease the accumulation of ROX metabolites in water spinach when treated with CM containing ROX and its metabolites.

The arsenic hyperaccumulator fern Pteris vittata L

Arsenic (As) contaminated soils and waters are becoming major global environmental and human health risks. The identification of natural hyperaccumulators of As opens the door for phytoremediation of the arsenic contaminant. Pteris vittata is the first identified naturally evolving As hyperaccumulator. More than a decade after its discovery, we have made great progress in understanding the uptake, transport, and detoxification of As in the fern. The molecular mechanisms controlling As accumulation in P. vittata are now beginning to be recognized. In this review, we will try to summarize what we have learned about this As accumulator, with particular emphasis on the current knowledge of the physiological and molecular mechanisms of arsenic phytoremediation. We also discuss the potential strategies to further enhance phytoextraction abilities of P. vittata.