Comparison of Root‐System Efficiency and Arsenic Uptake of Two Fern Species

Abstract

This greenhouse study examined the root characteristics (biomass, length, area, and diameter) and root uptake efficiency of Pteris vittata, an arsenic (As) hyperaccumulator and Nephrolepis exaltata, not an As hyperaccumulator, in relation to plant uptake of As and nutrients in an As‐contaminated and a control soil. After 8 weeks of growth, on a per plant basis, P. vittata accumulated 7.3–8.8 g of biomass and removed 2.51 mg of As from the As‐contaminated soil compared to 2.4–2.7 g of biomass and 0.09 mg of As for N. exaltata. This was partially because P. vittata developed a more extensive root system, 2.4–3.8 times greater (biomass, length, and area), and possessed a greater proportion of fine roots than N. exaltata. In addition, the As root‐uptake efficiency (defined as As concentrations in plant tissue per unit root) for fronds of P. vittata was 15–23 times greater than that of N. exaltata in both soils. Whereas N. exaltata removed phosphorus (P) more efficiently from the soils, P. vittata removed As more efficiently. The larger root biomass coupled with more efficient root‐uptake systems for As may have contributed to As hyperaccumulation by P. vittata.     

Arsenic and heavy metal accumulation by Athyrium yokoscense from contaminated soils

Abstract

Athyrium yokoscense, a type of fern that grows vigorously in mining areas in Japan, is well known as a Cd hyperaccumulator as well as a Cu, Pb and Zn tolerant plant. However, no information is available on As accumulation of A. yokoscense, although it often grows on soils containing high levels of both heavy metals and As. In this study, young ferns collected from a mine area were grown in media containing As-spiked soils or mine soil in a greenhouse for 21 weeks. Athyrium yokosense was highly tolerant to arsenate and survived in soils containing up to 500 mg As (V) kg^?1. The addition of 100 mg As (V) kg^?1 resulted in the highest fern biomass (1.95 g plant^?1) among As-spiked soils. Although the As concentration of the fern was lower than other As hyperaccumulators, such as Pteris vittata, A. yokoscense could hyperaccumulate As in mature and old fronds. Arsenic was accumulated most efficiently in old fronds (922 mg kg^?1) in the media containing 5 mg As (III) kg^?1. Moreover, higher As accumulation was found in the roots of the ferns, with a range from 506 to 2,192 mg kg^?1. In addition, in the mine soil with elevated concentrations of As and heavy metals, A. yokoscense not only hyperaccumulated As (242 mg As kg^?1 in old fronds), but also accumulated Cd, Pb, Cu and Zn at concentrations much higher than those reported for other terrestrial plants. Athyrium yokoscense accumulated Cd mostly in fronds in high concentrations, up to 1095 mg kg^?1, while it accumulated Cu, Zn and Pb mainly in the roots and the concentrations were 375, 2040 and 1165 mg kg^?1, respectively.     

Comparison of Arsenic and Phosphate Uptake and Distribution in Arsenic Hyperaccumulating and Nonhyperaccumulating Fern

Abstract

Uptake of arsenic (As) and its distribution in Chinese Brake fern (Pteris vittata L.), an As hyperaccumulator, and Boston fern (Nephrolepis exaltata L.), a nonhyperaccumulator, in the presence of phosphorus (P), were characterized by employing a hydroponic experiment with a complete three-factorial design. Two levels of As (100 and 1000 µM) and four levels of P (0, 100, 500, and 1000 µM) were used in this study. Arsenic uptake rates on the basis of root fresh weight for the two ferns were similar at low As concentration (100 µM). At high As concentration (1000 µM), however, As uptake rates (373–987 nmol g^?1 f wt h^?1) of P. vittata were significantly greater than those of N. exaltata (164–459 nmol g^?1 f wt h^?1). In both ferns, addition of P reduced their As uptake rate as well as accumulation. Pteris vittata had a greater As TF (Translocation factor = concentration ratio of fronds to roots) than N. exaltata. On the contrary, N. exaltata displayed a greater P TF than P. vittata. As a result, high P/As ratio was observed in the roots of P. vittata, whereas high P/As ratio was observed in the fronds of N. exaltata. The study illustrated that As hyperaccumulation by P. vittata may be facilitated by its high As influx rate and its high molar P/As ratio in the roots resulting from both high As TF and low P TF.     

Uptake,Translocation, and Transformation of Arsenic by Four Fern Species in Arsenic‐Spiked Soils

Arsenic (As) toxicity has become a global concern because of the ever‐increasing contamination of water, soil, and crops in many regions of the world. Although most plants are susceptible to As, some ferns are resistant to it and can accumulate As. In this study, four species of ferns, Asplenium nidus (AN), Pteris umbrosia (PU), Polypodium vulgare (PV), and Pteris cretica (PC), were screened for their ability to tolerate and hyperaccumulate As. Ferns were exposed to 120 mg As kg^?1 as sodium arsenate (Na₂HAsO₄) for 50 days under natural sunlight in greenhouse conditions, and the fronds and roots were analyzed for As speciation and selected macronutrients [potassium (K) and phosphorus (P)]. The species of ferns varied widely in their abilities to transport As to the fronds (ranged from 164 to 4820 mg kg^?1 DW) with the greatest frond As concentration found in PU (4820 mg kg^?1). The distribution of soil As fractions indicated that As was mostly bound carbonate (carb) (32.4%) and in the residual fractions (45.1%). Chemical fractionation of As‐spiked soil indicated that the greatest reduction in soil As after growing was in carb As form. Arsenic speciation analysis shows that >82% of the total As in the aboveground biomass is present as the reduced form of As, arsenite [As(III)], which is considered to be the more toxic form. However, in roots, only 60% of the As is present as As(III). Furthermore, among the four species of ferns, PU is the most promising to be used in the remediation of the affected area. Therefore, it is possible to use PU to remediate As‐contaminated soils by repeatedly harvesting its fronds.     

Determination of Zinc Phytoavailability in Soil by Diffusive Gradients in Thin Films

Assessment of zinc (Zn) phytoavailability by the newly developed technique of diffusive gradients in thin films (DGT) has started gaining more importance because of some advantages over routine soil extractants. A greenhouse study was conducted to determine Zn phytotoxicity thresholds and the phytoavailability of Zn to sorghum sudan (Sorghum vulgare var. sudanese) grass by DGT, compared with calcium chloride (CaCl₂) extraction. Treatments were five Zn levels and two soil pH (6.5 and 6). To obtain various amounts of Zn phytoavailability, soils having two different pH values were amended with zinc sulfate (ZnSO₄) at rates of 0, 150, 300, 600, and 1200 mg Zn kg^?1. Control soil (pH = 6.5) was treated with predetermined elemental sulfur to create different soil pH values (6). Shoot and root Zn concentrations ranged from 27 to 827 mg kg^?1 and 101 to 2858 mg kg^?1, respectively. In general, the Zn concentrations in shoots and roots were increased by increasing Zn concentrations and soil pH. Increasing applied Zn to soil decreased the plant biomass yield and increased adsorption of Zn by DGT. Calcium (Ca) to Zn ratios for all treatments except controls were <26 for shoots and <13 for roots. The CaCl₂‐extractable Zn and effective concentration (C_E) correlated well with plant Zn concentration. A critical shoot Zn concentration for 90% of the control yield was chosen as an indicator of Zn toxicity. The performance of DGT, CaCl₂ extraction, Ca/Zn ratio and plant Zn concentrations were similar for assessing Zn phytoavailability.     

Phytoextraction of cobalt (Co)-contaminated soils by sweet alyssum (Lobularia maritima (L.) Desv.) is enhanced by biodegradable chelating agents

Purpose

Combining biodegradable chelating agents with phytoextraction is an efficient technique to amend metal-contaminated soils, but most studies have addressed remediation efficiency rather than a comprehensive understanding of the interactions among plant stress, metal accumulation, and metal bioavailability. This study aimed to investigate the effects of biodegradable chelating agents on improving the efficiency of phytoextraction for cobalt (Co)-contaminated soil by sweet alyssum (Lobularia maritima (L.)) and to explore the interrelationships among plant stress, Co accumulation, and Co bioavailability.

Materials and methods

Sweet alyssum (three plants per pot) was grown in pots containing soil with Co added at 0, 40, and 60 mg kg^?1, respectively. After 70 days of growth, we added four biodegradable chelating agents (EDDS, NTA, CA, and OA) at various concentrations (0, 2.5, 5.0, and 7.5 mmol kg^?1). The plants were harvested after 7 days, and the biomass, reactive oxygen species (ROS) parameters, Co concentrations of the shoot and root, and available Co content in the soil were analyzed.

Results and discussion

The results demonstrate that chelating agents significantly (p?<?0.05) improved the phytoextraction capability of sweet alyssum and influenced plant growth and stress. The capability of EDDS to activate Co was higher than that of other chelating agents at identical concentrations in Co-contaminated soils. Furthermore, we observed that a moderate concentration (40 mg kg^?1) of Co could promote plant growth and that high concentrations of Co (60 mg kg^?1) and EDDS (7.5 mmol kg^?1) cause enhanced stress to plant growth, even resulting in lower shoot Co accumulation than that in the moderate EDDS treatment (5.0 mmol kg^?1).

Conclusions

The present study demonstrates that the application of EDDS may be a better choice for Co phytoextraction than NTA, CA, and OA; nevertheless, a high concentration of EDDS may enhance the negative effects on plant growth, physiological traits, and Co accumulation.

     

Chelate-enhanced phytoextraction and phytostabilization of lead-contaminated soils by carrot (Daucus carota)

The objective of this study was to study the influence of different ethylenediamine tetraacetate (EDTA), nitrilotriacetic acid (NTA) and oxalic acid (HOx) concentrations on tolerance and lead (Pb) accumulation capacity of carrot (Daucus carota). The results indicated that by increasing Pb, NTA and HOx concentrations in the soil, the shoot, taproot and capillary root dry matters increase effectively. In contrary, EDTA caused to reduce capillary roots biomass. EDTA was more effective than NTA and HOx in solubilizing soil Pb. The highest Pb content in shoots (342.2 ± 13.9 mg kg^?1) and taproots (301 ± 15.5 mg kg^?1) occurred in 10 mM EDTA, while it occurred for capillary roots (1620 ± 24.6 mg kg^?1) in 5 mM HOx, when the soil Pb concentration was 800 mg kg^?1. The obtained high phytoextraction and phytostabilization potentials were 1208 (±25.6) and 11.75 (±0.32) g Pb ha^?1 yr^?1 in 10 mmol EDTA kg^?1 soil and no chelate treatments, respectively. It may be concluded that chelate application increases Pb uptake by carrots. Consequently, this plant can be introduced as a hyperaccumulator to phytoextract and phytostabilize Pb from contaminated soils.     

Cadmium and zinc accumulation in willow and poplar species grown on polluted soils

Woody plant species that produce high biomass have been proposed for use in phytoremediation technology. We investigated the accumulation of cadmium (Cd) and zinc (Zn) in Salix babylonica, S. caprea, S. dasyclados, S. matsudana × alba, S. purpurea, S. smithiana, Populus tremula, and P. nigra clones grown in a pot experiment on a Calcaric and a Eutric Cambisol (pH 7.2 and 6.4) of different levels of contamination (total metal concentrations in mg kg^–1 in soil A: 32.7 Cd, 1760 Zn; soil B: 4.34 Cd, 220 Zn). Generally, the tested clones tolerated large metal concentrations in soils and had larger Cd and Zn concentrations in leaves compared to the roots. The largest Cd concentrations in leaves were found in two clones of S. smithiana (440 mg kg^–1 on soil A; 70 mg kg^–1 on soil B). One of the S. smithiana clones had also the largest Zn concentrations (870 mg kg^–1) on soil B but accumulated slightly less Zn than a S. matsudana × alba clone (2430 mg kg^–1) on soil A. The Cd concentrations in leaves of both S. smithiana clones on soil A are the largest ever reported for soil‐grown willows. The bioconcentration factors of the best performing clone reached 15.9 for Cd and 3.93 for Zn on the less contaminated soil B. Also based on the metal contents in leaves, this clone was identified as the most promising for phytoextraction. The metal concentrations in leaves observed in the pot experiment do not reflect those found in a previous hydroponic study and the leaf‐to‐root ratios are clearly underestimated in hydroponic conditions. This demonstrates the need for testing candidates for phytoextraction crops on soils rather than in hydroponics. Our data also show that the phytoextraction potential should be tested on different soils to avoid misleading conclusions.     

Phytoextraction of arsenic contaminated soil by Chinese brake fern (Pteris vittata): Effect on soil microbiological activities

A greenhouse experiment was conducted to investigate the effect of phytoextraction by Chinese brake fern (Pteris vittata L.) on microbial activity and biomass in arsenic-contaminated soil (naturally occurring arsenic-contaminated soils of West Bengal, India). P. vittata was grown for two successive growing cycles (4 months each) with two phosphate sources (di-ammonium phosphate (DAP) and single superphosphate (SSP)). After phytoextraction by P. vittata, the rhizosphere soils were analyzed for microbial biomass C (MBC), C mineralization (C_min), dehydrogenase activity (DHA), phosphomonoesterase activities, and aryl sulphatase activity. All enzyme activities increased after two successive growing cycles of P. vittata as compared to one growing cycle and unplanted control. The arsenic (As) phytoextraction by this fern also increased the MBC by 34 %, C_min by 63 %, DHA by 38 %, acid phosphomonoesterase activity by 30 %, alkaline phosphomonoesterase activity by 6 %, and aryl-sulphatase activity by 33 % with two successive growing cycles over unplanted control. The di-ammonium phosphate was better as compared to single super phosphate for enhancing microbiological and biochemical parameters except phosphomonoesterase activities.     

Arsenic Uptake by Two Hyperaccumulator Ferns from Four Arsenic Contaminated Soils

A greenhouse study was conducted to evaluate and compare arsenic accumulation from four arsenic contaminated soils by two arsenic hyperaccumulators, Pteris vittata and Pteris cretica. After growing in soils for six weeks, the plants were harvested and separated into above- and below-ground biomass. Total As, P, Ca, K, glutathione and biomass were measured for the plants, and total As, Mehlich-3 P and As, exchangeable K and Ca, and arsenic fractionation were performed for the soils. Pteris vittata had significantly higher total biomass (14 g/plant) and As accumulation than P. cretica. Arsenic accumulation in both ferns followed the arsenic concentrations in the soil. The P/As molar ratio in the fronds, growing in arsenic contaminated soils, ranged from 80 to 939 in P. vittata and 130 to 421 in P. cretica. Plant arsenic concentrations were significantly positively correlated with Mehlich-3 arsenic in the soils. Soil pH was also significantly correlated with Mehlich-3 arsenic before and after plant uptake. Plant As uptake was significantly correlated with exchangeable potassium in the soil before plant uptake. Glutathione availability was not implicated as a major detoxification mechanism in these ferns. Though both plants were effective in taking up arsenic from various arsenic contaminated soils, P. vittata was overall a better candidate for phytoremediation of arsenic contaminated soils.     

Effects of Lead and Zinc on Arsenic Accumulation in Nonmetallicolous and Metallicolous Populations of Pteris vittata L.

Although Pteris vittata L. can occur on arsenic (As)–contaminated soils and uncontaminated soils, variation in As accumulation among nonmetallicolous and metallicolous populations and impacts of heavy metals in soils on As accumulation in the nonmetallicolous and metallicolous populations have not been fully explored. Five populations of P. vittata were collected from different field sites, and sporelings (four or five fonds) were used to further investigate the pattern of As accumulation. The results of pot trials showed that three nonmetallicolous populations of P. vittata possessed an obviously greater growth rate than the two metallicolous populations. The nonmetallicolous populations also accumulated significantly greater (P < 0.05) As than the metallicolous populations, regardless of the presence or absence of lead (Pb) and zinc (Zn). In addition, Pb and Zn in soils decreased As accumulation in P. vittata. The present results suggested that As removal can be greatly enhanced by the judicious selection of populations of P. vittata.     

Coal Fly Ash and Phospho‐gypsum Mixture as an Amendment to Improve Rice Paddy Soil Fertility

Abstract

Rice is a plant that requires high levels of silica (Si). As a silicate (SiO₂) source to rice, coal fly ash (hereafter, fly ash), which has an alkaline pH and high available silicate and boron (B) contents, was mixed with phosphor‐gypsum (hereafter, gypsum, 50%, wt wt^?1), a by‐product from the production of phosphate fertilizer, to improve the fly ash limitation. Field experiments were carried out to evaluate the effect of the mixture on soil properties and rice (Oryza sativa) productivity in silt loam (SiL) and loamy sand (LS) soils to which 0 (FG 0), 20 (FG 20), 40 (FG 40), and 60 (FG 60) Mg ha^?1 were added. The mixture increased the amount of available silicate and exchangeable calcium (Ca) contents in the soils and the uptake of silicate by rice plant. The mixture did not result in accumulation of heavy metals in soil and an excessive uptake of heavy metals by the rice grain. The available boron content in soil increased with the mixture application levels up to 1.42 mg kg^?1 following the application of 60 Mg ha^?1 but did not show toxicity. The mixture increased significantly rice yield and showed the highest yields following the addition of 30–40 Mg ha^?1 in two soils. It is concluded that the fly ash and gypsum mixture could be a good source of inorganic soil amendments to restore the soil nutrient balance in rice paddy soil.     

Growth,survival, and heavy metal (Cd and Ni) uptake of spinach (Spinacia oleracea) and fenugreek (Trigonella corniculata) in a biochar‐amended sewage‐irrigated contaminated soil

Irrigation of arable land with contaminated sewage waters leads to the accumulation of trace metals in soils with subsequent phyto‐/zootoxic consequences. In this study, biochar derived from cotton sticks was used to amend an agricultural silt‐loam soil that had been previously irrigated with trace metal contaminated sewage waters. Metal accumulation and toxicity to spinach (Spinacia oleracea) and fenugreek (Trigonella corniculata) was investigated by measuring concentrations of Cd and Ni in plant tissues and various photosynthetic and biochemical activities of plants. Positive impacts of biochar on both spinach and fenugreek were observed in terms of biomass production that increased from 29% to 36% in case of spinach, while for fenugreek this increase was 32% to 36%. In the control treatment there was an increase in malondialdihyde, soluble sugar, and ascorbic acid contents, indicating heavy metal stress. Biochar applications increased soluble proteins and amino acids in plants and reduced the uptake of Cd from 5.42 mg kg^?1 at control to 3.45 mg kg^?1 at 5% biochar amended soil and Ni (13.8 mg kg^?1 to 7.3 mg kg^?1 at 5% biochar) by the spinach plants. In fenugreek, the Cd was reduced from 7.72 mg kg^?1 to 3.88 mg kg^?1 and reduction in Ni was from 15.45 mg kg^?1 to 9.46 mg kg^?1 at 5% biochar treated soil, reducing the possibility of transfer up the food chain. This study demonstrates that the use of biochar made from cotton‐sticks, as an amendment to arable soils that have received contaminated irrigation water, could improve plant growth and decrease Cd and Ni uptake to crops, alleviating some of the negative impacts of using sewage waters on arable land.     

Laboratory Assessment of Nostoc 9v (Cyanobacteria) Effects on N2 Fixation and Chemical Fertility of Degraded African Soils

The potential of Nostoc 9v for improving the nitrogen (N)₂–fixing capacity and nutrient status of semi‐arid soils from Tanzania, Zimbabwe, and South Africa was studied in a laboratory experiment. Nostoc 9v was inoculated on nonsterilized and sterilized soils. Inoculum rates were 2.5 mg dry biomass g^?1 soil and 5 mg dry biomass g^?1 soil. The soils were incubated for 3 months at 27 °C under 22 W m² illumination with a photoperiod of 16 h light and 8 h dark. The moisture was maintained at 60% of field capacity. In all soils, Nostoc 9v proliferated and colonized the soil surfaces very quickly and was tolerant to acidity and low nutrient availability. Cyanobacteria promoted soil N₂ fixation and had a pronounced effect on total soil organic carbon (SOC), which increased by 30–100%. Total N also increased, but the enrichment was, in most soils, comparatively lower than for carbon (C). Nitrate and ammonium concentrations, in contrast, decreased in all the soils studied. Increases in the concentration of available macronutrients were produced in most soils and treatments, ranging from 3 to 20 mg phosphorus (P) kg^?1 soil, from 5 to 58 mg potassium (K) kg^?1 soil, from 4 to 285 mg calcium (Ca) kg^?1, and from 12 to 90 mg magnesium (Mg) kg^?1 soil. Positive effects on the levels of available manganese (Mn) and zinc (Zn) were also observed.     

铅锌矿区分离丛枝菌根真菌对万寿菊生长与吸镉的影响

盆栽试验研究了土壤不同施Cd水平(0、20、50 mg kg-1)下,接种矿区污染土壤中丛枝菌根真菌对万寿菊根系侵染率、植株生物量及Cd吸收与分配的影响。结果表明:接种丛枝菌根真菌显著提高了Cd胁迫下万寿菊的根系侵染率和植株生物量;随着施Cd水平提高,各处理植株Cd浓度和Cd吸收量显著增加。各施Cd水平下万寿菊地上部Cd吸收量远远高于根系Cd吸收量,尤其在20 mg kg-1施Cd水平下,接种处理地上部Cd吸收量是根系的3.90倍,对照处理地上部Cd吸收量是根系的2.33倍;同一施Cd水平下接种处理地上部Cd吸收量要显著高于对照。总体上,试验条件下污染土壤中分离的丛枝菌根真菌促进了万寿菊对土壤中Cd的吸收,并增加了Cd向地上部分的运转,表现出植物提取的应用潜力。     

Bioavailability and Accumulation of Cadmium and Zinc by Sedum plumbizincicola after Liming of an Agricultural Soil Subjected to Acid Mine Drainage

A glasshouse pot experiment was conducted to study the effects of liming on plant growth and zinc (Zn) and cadmium (Cd) accumulation by Sedum plumbizincicola in a heavy-metal-contaminated acidified paddy soil. Lime application significantly increased the soil pH, which reached a maximum of 5.53 after addition of 4.0 g kg^?1 lime to soil, about 1.4 units more than that of the control. Sedum plumbizincicola grew larger after lime application but aboveground biomass did not increase significantly with increasing soil pH. Liming significantly reduced shoot Zn and Cd concentrations and uptake except at the lowest lime application rate (0.5 g kg^?1 lime to soil). This indicates that S. plumbizincicola can grow well in acidic soil at a soil pH of 4.15, and application of lime did not increase plant heavy-metal extraction. Consequently, it is promising to use this plant for Cd and Zn phytoextraction from agricultural soils polluted with acid and metals.     

Soil properties affecting solid–liquid distribution of As(V) in soils

The prediction of the mobility of arsenic (As) is crucial for predicting risks in soils contaminated with As. The objective of this study is to predict the distribution of As between solid and solution in soils based on soil properties and the fraction of As in soil that is reversibly adsorbed. We studied adsorption of As(V) in suspensions at radiotrace concentrations for 30 uncontaminated soils (pH 4.4–6.6). The solid–liquid distribution coefficient of As (K_d) varied from 14 to 4430 l kg^?1. The logarithm of the concentration of oxalate‐extractable Fe explained 63% of the variation in log K_d; by introducing the logarithm of the concentration of oxalate‐extractable P in the regression model, 85% of the variation in log K_d is explained. Double labelling experiments with ⁷³As(V) and ³²P(V) showed that the As to P adsorption selectivity coefficient decreased from 3.1 to 0.2 with increasing degree of P saturation of the amorphous oxides. The addition of As(V) (0–6 mmol kg^?1) reduced the K_d of ⁷³As up to 17‐fold, whereas corresponding additions of P(V) had smaller effects. These studies suggest that As(V) is adsorbed to amorphous oxides in soils and that sites of adsorption vary in their selectivity in respect of As and P. The concentration of isotopically exchangeable As in 27 contaminated soils (total As 13–1080 mg kg^?1) was between 1.2 and 19% (mean 8.2%) of its total concentration, illustrating that a major fraction of As is fixed. We propose a two‐site model of competitive As(V)–P(V) sorption in which amorphous Fe and Al oxides represent the site capacity and the isotopically exchangeable As represents the adsorbed phase. This model is fitted to ⁷³As adsorption data of uncontaminated soils and explains 69% of the variation of log K_d in these soils. The log K_d in contaminated soils predicted using this two‐site model correlated well with the observed log K_d (r = 0.75). We conclude that solubility of As is related to the available binding sites on amorphous oxides and to the fraction of As that is fixed.     

Dissolution of Dominant Soil Phosphorus Fractions in Phosphorus-Responsive Soils of Bihar,India: Effects of Mycorrhiza and Fertilizer Levels

We investigated the effects of Arbuscular Mycorrhiza (AM) fungi and various phosphorus (P) levels on the distribution and availability of P in dominant soils of Bihar, India. Potassium chloride (KCl)-P (labile P), sodium hydroxide (NaOH)-P (Fe-Al-bound P), hydrochloric acid (HCl)-P (Ca-bound P), and residual P (Res-P) fractions were analyzed in the soils under maize plant. Ca-bound P was the most abundant P fraction in the alkaline soils (65% of the total P) followed by neutral soil (35% of the total P), whereas it was less abundant (<4%) in the acidic soil type. Fe-Al-bound P was found to be highest for acidic soil (65% of the total P). Soils under the inoculation with Glomus mossae and control gave the highest and lowest values (15.63 mg kg^?1 and 10.74 mg kg^?1 respectively) for the labile fraction which was similar to the organically bound residual fractions of P (200.17 mg kg^?1 and 193.66 mg kg^?1 respectively. Inoculation of the soils with AM fungi leads to the redistribution of P fractions in different soils which consequently helps in improvement of available P in soil conducive for plant uptake.     

Metal uptake in maize, willows and poplars on impoldered and freshwater tidal marshes in the Scheldt estuary

Foliar Cd and Zn concentrations in Salix, Populus and Zea mays grown on freshwater tidal marshes were assessed. Soil metal concentrations were elevated, averaging 9.7 mg Cd kg^?1 dry soil, 1100 mg Zn kg^?1 dry soil and 152 mg Cr kg^?1 dry soil. Cd (1.1–13.7 mg kg^?1) and Zn (192–1140 mg kg^?1) concentrations in willows and poplars were markedly higher than in maize on impoldered tidal marshes (0.8–4.8 mg Cd kg^?1 and 155–255 mg Zn kg^?1). Foliar samples of maize were collected on 90 plots on alluvial and sediment‐derived soils with variable degree of soil pollution. For soil Cd concentrations exceeding 7 mg Cd kg^?1 dry soil, there was a 50% probability that maize leaf concentrations exceeded public health standards for animal fodder. It was shown that analysis of foliar samples of maize taken in August can be used to predict foliar metal concentrations at harvest. These findings can therefore contribute to anticipating potential hazards arising from maize cultivation on soils with elevated metal contents.