Phytoextraction of copper from contaminated soil by Elsholtzia splendens as affected by EDTA, citric acid, and compost

Phytoextraction of copper (Cu) from contaminated soils greatly depends on the metal bioavailability in the soils and metal uptake ability of the plant. In this study, the effects of chelators [ethylenediamine tetraacetic acid (EDTA), citric acid (CA)] and compost amendments on Cu phytoextraction potential by a tolerant and accumulating plant species (E. splendens) were examined in two types of contaminated soils, ie., the mined soil from Cu-mined area (MS) and a paddy soil polluted by Cu refining (PS). The results showed that EDTA application at 2.5-5.0 mmol kg(-1) increased phytoextraction of Cu by four- and eight-fold from both MS and PS, respectively, which is mainly attributed to increased H2O extractable Cu in the soil. The Cu amount extracted by the shoots of E. splendens reached 800-1000 microg Cu plant(-1) from the MS and 400-700 microg Cu plant(-1) from the PS at EDTA application rates of 2.5-5.0 mmol kg(-1). The application of CA at 5.0 mmol kg(-1) had minimal effects on Cu extractability in both soils and slightly decreased Cu extraction efficiency by E. splendens. Plant biomass production was enhanced by CA at 0.25 mmol L(-1) in nutrient solution, but inhibited by CA at 5.0 mmol kg(-1) in both MS and PS. Increasing the compost rate significantly decreased H2O extractable Cu in the MS, but raised H2O-extractable Cu in the PS, which resulted mainly front the reduced exchangeable Cu in the MS and the increased exchangeable and organic fractions of Cu in the PS by compost. At high compost rate (5%), the shoots of E. splendens extracted 3.6-fold higher Cu from the PS than from the MS. These results indicate that, among the soil amendments, efficiency of Cu phytoextraction is enhanced mostly by 2.5-5.0 mmol kg(-1) EDTA, followed by 5% (w:w) compost, whereas < 5.0 mmol kg(-1) CA has minimal effects on Cu phytoextraction by E. splendens in the PS. As for the MS, only 2.5-5.0 mmol kg(-1) EDTA can elevate the efficiency of Cu, while 5% compost amendment and < 5.0 mmol kg(-1) CA application have no marked effects on Cu phytoextraction by E. splendens.     

Phytoextraction of zinc, copper, nickel and lead from a contaminated soil by different species of Brassica

In a pot culture experiment, five different species of Brassica (Brassica juncea, Brassica campestris, Brassica carinata, Brassica napus, and Brassica nigra) were grown for screening possible accumulators of heavy metals, viz. Zn, Cu, Ni, and Pb. The plants were grown to maturity in a soil irrigated with sewage effluents for more than two decades in West Delhi, India. The soil analysis showed enhanced accumulation of Zn, Cu, Ni, and Pb in this sewage-irrigated soil. Among all species, B. carinata showed the highest concentration (mg kg(-1)) as well as uptake (microg pot(-1)) of Ni and Pb at maturity. Although B. campestris showed a higher concentration of Zn in its shoots (stem plus leaf), B. carinata extracted the largest amount of this metal due to greater biomass production. However, B. juncea phytoextracted the largest amount of Cu from the soil. In general, the highest concentration and uptake of metal was observed in shoots compared to roots or seeds of the different species. Among the Brassica spp., B. carinata cv. DLSC1 emerged as the most promising, showing greater uptake of Zn, Ni, and Pb, while B. juncea cv. Pusa Bold showed the highest uptake of Cu. The B. napus also showed promise, as it ranked second with respect to total uptake of Pb, Zn, and Ni, and third for Cu. Total uptake of metals by Brassica spp. correlated negatively with available as well as the total soil metal concentrations. Among the root parameters, root length emerged as the powerful parameter to dictate the uptake of metals by Brassica spp. Probably for the first time, B. carinata was reported as a promising phytoextractor for Zn, Ni, and Pb, which performed better than B. juncea.     

Phytoremediation of arsenic contaminated soil by Pteris vittata L. II. Effect on arsenic uptake and rice yield

A greenhouse experiment evaluated the effect of phytoextraction of arsenic from a contaminated soil by Chinese Brake Fern (Pteris vittata L.) and its subsequent effects on growth and uptake of arsenic by rice (Oryza sativa L.) crop. Pteris vittata was grown for one or two growing cycles of four months each with two phosphate sources, using single super phosphate (SSP) and di-ammonium phosphate (DAP). Rice was grown on phytoextracted soils followed by measurements of biomass yield (grain, straw, and root), arsenic concentration and, uptake by individual plant parts. The biomass yield (grain, straw and rice) of rice was highest in soil phytoextracted with Pteris vittata grown for two cycles and fertilized with diammonium phosphate (DAP). Total arsenic uptake in contaminated soil ranged from 8.2 to 16.9 mg pot(-1) in first growing cycle and 5.5 to 12.0 mg pot(-1) in second growing cycle of Pteris vittata. There was thus a mean reduction of 52% in arsenic content of rice grain after two growing cycle of Pteris vittata and 29% after the one growing cycle. The phytoextraction of arsenic contaminated soil by Pteris vittata was beneficial for growing rice resulted in decreased arsenic content in rice grain of <1 ppm. There was a mean improvement in rice grain yield 14% after two growing cycle and 8% after the one growing cycle of brake fern.     

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.     

Transient Phytoextraction Agents: Establishing Criteria for the Use of Chelants in Phytoextraction of Recalcitrant Metals

The phytoremediation of recalcitrant metals such as lead and uranium rely on soil amendments to enhance metal availability within the rhizosphere. Because these amendments may persist in soils, agents that not only biodegrade rapidly but also are effective in triggering metal uptake in plants are needed for metals phytoextraction to be considered as an accepted practice. In this study, several biodegradable organic acids and chelating agents were assessed to determine if these amendments can be used in an effective manner, and if their activity and use is consistent with a proposed class of soil amendments for phytoextraction, here termed transient phytoextraction agents (TPAs). A TPA is proposed as an agent that would exhibit both effectiveness in triggering plant accumulation of the targeted metal while minimizing the risk of migration through rapid degradation or inactivation of the soluble complex. Eleven candidate TPAs (acetic acid, ascorbic acid, citric acid, malic acid, oxalic acid, succinic acid, ethylenediaminedisuccinic acid, dicarboxymethylglutamic acid, nitrilotriacetic acid, BayPure® CX 100, and the siderophore desferrioxamine B) were tested in batch studies to evaluate their complexation behavior using contaminated soils, with uranium and lead as the target metals. A growth chamber study was then conducted with Brassica juncea (Indian mustard), Helianthus annuus (sunflower), and Festuca arundinacea (tall fescue) grown in a lead-contaminated soil that was treated with the candidate TPAs to assess phytoextraction effectiveness. For the soils tested, citric acid, oxalic acid, and succinic acid were found to be effective complexing agents for uranium phytoextraction, whereas Baypure® CX 100 and citric acid exhibited effectiveness for lead phytoextraction.     

Phytoextraction of soil cadmium and zinc by microbes-inoculated Indian mustard (Brassica juncea)

Abstract

A pot experiment was carried out to evaluate the effect of Pseudomonas fluorescens and Trichoderma harzianum inoculation on the uptake of zinc (Zn) and cadmium (Cd) by Indian mustard (Brassica juncea) from the soil having three different concentrations of Zn (300, 600, 900 mg/kg) and Cd (5, 10, 15 mg/kg) separately. Microbial inoculation resulted in significantly better plant growth, available metal content and their uptake than control (without microbes). Available Zn was enhanced, ca.1.6- and 1.4-fold and Cd ca. 2.5- and 1.8-fold, by P. fluorescens and T. harzianum, respectively. P. fluorescens resulted in an increase in Zn uptake by 113.9, 51.9 and 58.4% and T. harzianum by 42.6, 32.1 and 33.9% over control from soils having 300, 600 and 900 mg Zn, respectively, while of the corresponding results for Cd were 110.2, 48.9 and 58.1% with P. fluorescens and 42.6, 30.9 and 33.4% with T. harzianum from soil having 5, 10 and 15 mg Cd, respectively, after 90 days of treatment. In general the rate of metal uptake was higher during the initial 30 days and declined later.     

Chelator-assisted phytoextraction of arsenic,cadmium and lead by Pteris vittata L. and soil microbial community structure response

Abstract

Using biodegradable chelators to assist in phytoextraction may be an effective approach to enhance the heavy-metal remediation efficiencies of plants. A pot experiment was conducted to investigate the effects of ethylenediamine disuccinic acid (EDDS), citric acid (CA), and oxalic acid (OA) on the growth of the arsenic (As) hyperaccumulator Pteris vittata L., its arsenic (As), cadmium (Cd), and lead (Pb) uptake and accumulation, and soil microbial responses in multi-metal(loid)-contaminated soil. The addition of 2.5-mmol kg^?1 OA (OA-2.5) produced 26.7 and 14.9% more rhizoid and shoot biomass, respectively compared with the control, while EDDS and CA treatments significantly inhibited plant growth. The As accumulation in plants after the OA-2.5 treatment increased by 44.2% and the Cd and Pb accumulation in plants after a 1-mmol kg^?1 EDDS treatment increased by 24.5 and 19.6%, respectively. Soil urease enzyme activities in OA-2.5 treatment were significantly greater than those in the control and other chelator treatments (p?<?0.05). A PCR–denatured gradient gel electrophoresis analysis revealed that with the addition of EDDS, CA and OA enhanced soil microbial diversity. It was concluded that the addition of OA-2.5 was suitable for facilitating phytoremediation of soil As and did not have negative effects on the microbial community.     

Comparison of EDTA- and Citric Acid-Enhanced Phytoextraction of Heavy Metals in Artificially Metal Contaminated Soil by Typha Angustifolia

A pot experiment was conducted to study the performance of EDTA and citric acid (CA) addition in improving phytoextraction of Cd, Cu, Pb, and Cr from artificially contaminated soil by T. angustifolia. T. angustifolia showed the remarkable resistance to heavy metal toxicity with no visual toxic symptom including chlorosis and necrosis when exposed to metal stress. EDTA-addition significantly reduced plant height and biomass, compared with the control, and stunted plant growth, while 2.5 and 5 mM CA addition induced significant increases in root dry weight. EDTA, and 5 and 10 mM CA significantly increased shoot Cd, Pb, and Cr concentrations compared with the control, with EDTA being more effective. At final harvest, the highest shoot Cd, Cr, and Pb concentrations were recorded in the treatment of 5 mM EDTA addition, while maximal root Pb concentration was found at the 2.5 mM CA treatment. However, shoot Cd accumulation in the 10 mM CA treatment was 36.9% higher than that in 2.5 mM EDTA, and similar with that in 10 mM EDTA. Shoot Pb accumulation was lower in 10 mM CA than that in EDTA treatments. Further, root Cd, Cu, and Pb accumulation of CA treatments and shoot Cr accumulation in 5 or 10 mM CA treatments were markedly higher than that of control and EDTA treatments. The results also showed that EDTA dramatically increased the dissolution of Cu, Cr, Pb, and Cd in soil, while CA addition had less effect on water-soluble Cu, Cr, and Cd, and no effect on Pb levels. It is suggested that CA can be a good chelator candidate for T. angustifolia used for environmentally safe phytoextraction of Cd and Cr in soils.     

Selecting appropriate forms of nitrogen fertilizer to enhance soil arsenic removal by Pteris vittata: a new approach in phytoremediation

Certain plant species have been shown to vigorously accumulate some metals from soil, and thus represent promising and effective remediation alternatives. In order to select the optimum forms of nitrogen (N) fertilizers for the arsenic (As) hyperaccumulator, Pteris vittata L., to maximize As extraction, five forms of N were added individually to different treatments to study the effect of N forms on As uptake of the plants under soil culture in a greenhouse. Although shoot As concentration tended to decrease and As translocation from root to shoot was inhibited, overall As accumulation was greater due to higher biomass when N fertilizer was added. Arsenic accumulation in plants with N fertilization was 100-300% more than in the plants without N fertilization. There were obvious differences in plant biomass and As accumulation among the N forms, i.e., NH4HCO3, (NH4)2S04, Ca(NO3)2, KNO3, urea. The total As accumulation in the plants grown in As-supplied soil, under different forms of N fertilizer, decreased as NH4HCO3>(NH4)2S04 > urea > Ca(NO3)2 >KNO3>CK. The plants treated with N and As accumulated up to 5.3-7.97 mg As/pot and removed 3.7-5.5% As from the soils, compared to approximately 2.3% of As removal in the control. NH4+ -N was apparently more effective than other N fertilizers in stimulating As removal when soil was supplied with As at initiation. No significant differences in available As were found among different forms of N fertilizer after phytoremediation. It is concluded that NH4+ -N was the preferable fertilizer for P. vittata to maximize As removal.     

Phytoextraction of weathered p,p'-DDE by zucchini (Cucurbita pepo) and cucumber (Cucumis sativus) under different cultivation conditions

Previous studies have shown that zucchini (Cucurbita pepo) and cucumber (Cucumis sativus) under field conditions are good and poor accumulators, respectively, of persistent organic pollutants from soil. Here, each species was grown under three cultivation regimes: dense (five plants in 5 kg soil): nondense (one plant in 80 kg soil): and field conditions (two to three plants in approximately 789 kg soil). p,p'-DDE and inorganic element content in roots, stems, leaves, and fruit were determined. In addition. rhizosphere, near-root, and unvegetated soil fractions were analyzed for concentrations of 11 low-molecular-weight organic acids (LMWOA) and 14 water-extractable inorganic elements. Under field conditions, zucchini phytoextracted 1.3% of the weathered p,p'-DDE with 98% of the contaminant in the aerial tissues. Conversely, cucumber removed 0.09% of the p,p'-DDE under field conditions with 83% in the aerial tissues. Under dense cultivation, cucumber produced a fine and fibrous root system not observed in our previous experiments and phytoextracted 0.78% of the contaminant, whereas zucchini removed only 0.59% under similar conditions. However. cucumber roots translocated only 5.7% of the pollutant to the shoot system, while in zucchini 48% of the p,p'-DDE in the plant was present in the aerial tissue. For each species, the concentrations of LMWOA in soil increased with increasing impact by the root system both within a given cultivation regime (i.e., rhizosphere > near-root > unvegetated) and across cultivation regimes (i.e., dense > nondense > field conditions). Under dense cultivation, the rhizosphere concentrations of LMWOAs were significantly greater for cucumber than for zucchini; no species differences were evident in the other two cultivation regimes. To enable direct comparison across cultivation regimes, total in planta p,p'-DDE and inorganic elements were mass normalized or multiplied by the ratio of plant mass to soil mass. For cucumber, differences in total p,p'-DDE and inorganic element content among the cultivation regimes largely disappear upon mass normalization, indicating that greater uptake of both types of constituents in the dense condition is due to greater plant biomass per unit soil. Conversely, for zucchini the mass normalized content of p,p'-DDE and inorganic elements is up to two orders of magnitude greater under field conditions than under dense cultivation, indicating a unique physiological response of C. pepo in the field. The role of cultivation conditions and nutrient availability in controlling root morphology, organic acid exudation, and contaminant uptake is discussed.     

Phytoextraction of nitrogen and phosphorus by crops grown in a heavily manured Dark Brown Chernozem under contrasting soil moisture conditions

Phytoextraction of excess nutrients by crops in soils with a long history of manure application may be a viable option for reducing the nutrient levels. This greenhouse study examined the effectiveness of six growth cycles (40 d each) of barley, canola, corn, oat, pea, soybean, and triticale at extracting nitrogen (N) and phosphorus (P) from a Dark Brown Chernozem that had received 180 Mg ha^?1 (wet wt.) of beef cattle feedlot manure annually for 38 years. Moisture content during the study was maintained at either 100% or 50% soil field capacity (SFC). Repeated cropping resulted in an overall decrease in dry matter yield (DMY). The decrease in N and P uptake relative to Cycle 1 was fastest for the cereal grains and less pronounced for the two legumes. However, cumulative N uptake values were significantly greater for corn than the other crops under both moisture regimes. The reduction in soil N was greater under the 100% than the 50% SFC. These results indicate that repeated cropping can be a useful management practice for reducing N and P levels in a heavily manured soil. The extent of reduction will be greater for crops with high biomass production under adequate moisture supply.     

The role of phytoplankton in the removal of arsenic by sedimentation from surface waters

The role of phytoplankton in the removal of arsenic (As) by particle adsorption and sedimentation was investigated in Moira Lake, Canada. Sampling water and suspended particles over one year illustrated significant variation in As partitioning between particulate and aqueous phases, but failed to establish a correlation between the partition coefficient, K _d, and indicators of phytoplankton biomass. A highly significant inverse logarithmic relationship was noted between K _d and the concentration of suspended particles (log K _d = 5.1 – 1.4 log SS; p = 0.0001) in an apparent demonstration of the particle concentration effect (O' Connor & Connolly, 1980).Particle deposition, measured by means of sediment traps, appeared to include a substantial component of resuspended surficial sediment making sediment trap results unreliable for quantifying the removal of substances from the water column. The As concentration of particles from deep traps deployed during late summer and early fall exceeded the As concentrations of suspended particles and surficial sediment, and may indicate that a highly contaminated nepheloid layer acts as a temporary sink for As.     

Phytoextraction potential of water fern (Azolla pinnata) in the removal of a hazardous dye,methyl violet 2B: Artificial neural network modelling

This study investigated the potential of Azolla pinnata (AP) in the removal of toxic methyl violet 2B (MV) dye wastewater using the phytoextraction approach with the inclusion of an Artificial Neural Network (ANN) modelling. Parameters examined included the effects of dye concentration, pH and plant dosage. The highest removal efficiency was 93% which was achieved at a plant dosage of 0.8 g (dye volume = 200 mL, initial pH = 6.0, initial dye concentration = 10 mg L^?1). A significant decrease in relative frond number (RFN), a growth rate estimator, observed at a dye concentration of 20 mg L^?1 MV indicated some toxicity, which coincided with the plant pigments studies where the chlorophyll a content was lower than the control. There were little differences in the plant pigment contents between the control and those in the presence of dye (5 to 15 mg L^?1) indicating the tolerance of AP to MV at lower concentrations. A three-layer ANN model was optimized (6 neurons in the hidden layer) and successfully predicted the phytoextraction of MV (R = 0.9989, RMSE = 0.0098). In conclusion, AP proved to be a suitable plant that could be used for the phytoextraction of MV while the ANN modelling has shown to be a reliable method for the modelling of phytoextraction of MV using AP.     

外源磷或有机质对板蓝根吸收转运砷的影响

采用土壤培养方法,研究了不同含砷水平土壤中添加外源磷或有机质对砷在板蓝根地下部和地上部累积与分配的影响。结果表明,在外源添加磷或者有机质的情况下,与自然土相比含砷土对板蓝根的生长有一定的促进作用;在自然土(13.4 mg/kg)中,外源磷没有明显影响板蓝根地下部对砷的累积,却显著降低了砷由地下部向地上部的转运,并且添加200 mg P2 O5/kg显著降低了砷在地上部的累积。然而,在含砷土(33.4 mg/kg)中,100 mg P2O5/kg处理显著降低了砷在地下部的累积,但随磷用量的增加反而促进了地下部砷的累积;在添加有机质试验中,10 g/kg的有机质显著降低了自然土中板蓝根地下部和地上部对砷的累积,并且砷的吸收能力也明显下降。在含砷土(23.4 mg/kg)中,添加5 g/kg的有机质不仅降低了砷在板蓝根中的富集,而且降低了其对砷的吸收能力,提高了砷由地下部向地上部的转运,但是随着有机质施用量增至10 g/kg,地下部砷含量及其吸收砷的能力均有一定程度的增大。因此,在砷水平较低的自然土壤上种植板蓝根添加200 mg P2O5/kg和10 g/kg的有机质是控制砷在该草药体内积累的适宜用量,而在砷水平较高的土壤上100 mg P2O5/kg和5 g/kg的有机质是降低板蓝根体内砷累积的适宜用量。     

Shoot and root growth and nutrients uptake of wheat as affected by soil layers

The effect of soil layering on the growth and nutrient content of wheat shoots and roots was studied. PVC containers (120 cm long and 25 cm inside diameter) were filled with layers of loam and loamy sand. Both roots and shoots dry weight increased as the thickness of loam layer increased. The root:shoot ratios decreased throughout the growing season. The N, P and K content of the shoots peaked at two weeks before anthesis, while shoot dry weight peaked at anthesis. The ranges of shoot content of N, P and K at anthesis for the different treatments were 6–25, 8–25 and 5–25% of the total plant nutrients, respectively. Late in the season the translocation rate of nutrients from the shoots to the seeds were in the following order N>P>K.     

Phytoextraction Potential of Poplar (Populus alba L. var. pyramidalis Bunge) from Calcareous Agricultural Soils Contaminated by Cadmium

To investigate the phytoextraction potential of Populus alba L. var. pyramidalis Bunge for cadmium (Cd) contaminated calcareous soils, a concentration gradient experiment and a field sampling experiment (involving poplars of different ages) were conducted. The translocation factors for all experiments and treatments were greater than 1. The bioconcentration factor decreased from 2.37 to 0.25 with increasing soil Cd concentration in the concentration gradient experiment and generally decreased with stand age under field conditions. The Cd concentrations in P. pyramidalis organs decreased in the order of leaves > stems > roots. The shoot biomass production in the concentration gradient experiment was not significantly reduced with soil Cd concentrations up to or slightly over 50 mg kg^–1. The results show that the phytoextraction efficiency of P. pyramidalis depends on both the soil Cd concentration and the tree age. Populus pyramidalis is most suitable for remediation of slightly Cd contaminated calcareous soils through the combined harvest of stems and leaves under actual field conditions.     

Novel approaches for examining the effects of differential soil compaction on xylem sap abscisic acid concentration, stomatal conductance and growth in barley (Hordeum vulgare L.)

Novel techniques were devised to explore the mechanisms mediating the adverse effects of compacted soil on plants. These included growing plants in: (i) profiles containing horizons differing in their degree of compaction and; (ii) split-pots in which the roots were divided between compartments containing moderately (1·4 g cm ^{? 3}) and severely compacted (1·7 g cm ^{? 3}) soil. Wild-type and ABA-deficient genotypes of barley were used to examine the role of abscisic acid (ABA) as a root-to-shoot signal. Shoot dry weight and leaf area were reduced and root : shoot ratio was increased relative to 1·4 g cm ^{? 3} control plants whenever plants of both genotypes encountered severely compacted horizons. In bartey cultivar Steptoe, stomatal conductance decreased within 4 d of the first roots encountering 1·7 g cm ^{? 3} soil and increased over a similar period when roots penetrated from 1·7 g cm ^{? 3} into 1·4 g cm ^{? 3} soil. Conductance was again reduced by a second 1·7 g cm ^{? 3} horizon. These responses were inversely correlated with xylem sap ABA concentration. No equivalent stomatal responses occurred in Az34 (ABA deficient genotype), in which the changes in xylem sap ABA were much smaller. When plants were grown in 1·7 : 1·4 g cm ^{? 3} split-pots, shoot growth was unaffected relative to 1·4 g cm ^{? 3} control plants in Steptoe, but was significantly reduced in Az34. Excision of the roots in compacted soil restored growth to the 1·4 g cm ^{? 3} control level in Az34. Stomatal conductance was reduced in the split-pot treatment of Steptoe, but returned to the 1·4 g cm ^{? 3} control level when the roots in compacted soil were excised. Xylem sap ABA concentration was initially higher than in 1·4 g cm ^{? 3} control plants but subsequently returned to the control level; no recovery occurred if the roots in compacted soil were left intact. Xylem sap ABA concentration in the split-pot treatment of Az34 was initially similar to plants grown in uniform 1·7 g cm ^{? 3} soil, but returned to the 1·4 g cm ^{? 3} control level when the roots in the compacted compartment were excised. These results clearly demonstrate the involvement of a root-sourced signal in mediating responses to compacted soil; the role of ABA in providing this signal and future applications of the compaction procedures reported here are discussed.     

Telomere length analysis in residents of a community exposed to arsenic

Differentiated cells telomere length is an indicator of senescence or lifespan; however, in peripheral blood leukocytes the relative shortening of the telomere has been considered as a biological marker of aging, and lengthening telomere as an associated risk to cancer. Individual’s age, type of tissue, lifestyle, and environmental factors make telomere length variable. The presence of environmental carcinogens such as arsenic (As) influence as causal agents of these alterations, the main modes of action for As described are oxidative stress, reduction in DNA repair capacity, overexpression of genes, alteration of telomerase activity, and damage to telomeres. The telomeres of leukocytes resulting a finite capacity of replication due to the low or no activity of the telomerase enzyme, therefore, elongation telomere in this kind of cells is a potential biological marker associated with the development of chronic diseases and carcinogenesis.     

施用有机肥对高砷红壤中小白菜砷吸收的影响

通过盆栽试验,研究了施用猪粪和鸡粪条件下红壤中的砷对小白菜生长和吸收的影响及土壤有效态砷含量的变化.结果表明：向高砷红壤中施用猪粪和鸡粪两种有机肥均使小白菜的生物量有不同程度的增加,其中,施用猪粪处理的小白菜生物量显著高于对照处理(P<0.05);猪粪和鸡粪两种有机肥的施用可导致土壤有效砷含量明显提高,施用猪粪后土壤有效砷含量增幅达394.9%～1033.6%,而施用鸡粪的土壤有效砷含量增幅为30.4%～94.1%; 施用有机肥明显促进了小白菜对砷的吸收,其中猪粪处理下小白菜的砷吸收量比对照增加20.7%～53.9%. 根据本研究结果,对砷含量较高的高风险农田,施用猪粪、鸡粪等有机肥可能会在一定程度上提高土壤有效砷含量和作物对砷的吸收量,使农产品质量和环境风险增加.