ANTIOXIDANT DEFENSE MECHANISM IN PIGEON PEA UNDER COBALT STRESS

Influence of excess cobalt (Co; 10 to 400 μM Co) on growth, biomass, Co accumulation, photosynthetic pigments, lipid peroxidation, proline, non-protein thiols and cysteine contents as well as activities of anti-oxidative enzymes was studied in pigeon pea (Cajanus cajan Mill). In pigeon pea leaves decreased concentrations of chlorophyll and carotenoids on exposure to excess Co was associated with decrease activity of catalase and super oxide dismutase and suggest antiperoxidative nature of excess Co. However, a marked increase in the activities of ascorbate peroxidase and peroxidase and enhanced levels of cysteine, non-protein thiols, and proline are suggestive of induction of antioxidants in excess Co. The threshold of toxicity (10% growth reduction) and toxicity (33% growth reduction) values of Co in pigeon pea were 75 and 160 μg g^?1in leaves, 42 and 180 μg g^?1in stem and 50 and 340 μg g^?1Co in roots, respectively.     

Enhanced Heavy Metal Phytoextraction from Marine Dredged Sediments Comparing Conventional Chelating Agents (Citric Acid and EDTA) with Humic Substances

Metal (Cu, Mn, Ni, Zn, Fe) concentrations in marine sediment and zooplankton were investigated in Izmir Bay of the Eastern Aegean Sea, Turkey. The study aimed to assess the levels of metal in different environmental compartments of the Izmir Bay. Metal concentrations in the sediment (dry weight) ranged between 4.26–70.8 μg g^?1 for Cu, 233–923 μg g^?1 for Mn, 14.9–127 μg g^?1 for Ni, 25.6–295 μg g^?1 for Zn, 12,404–76,899 μg g^?1 for Fe and 38,226–91,532 μg g^?1 for Al in the Izmir Bay. Maximum metal concentrations in zooplankton were observed during summer season in the inner bay. Significant relationships existed between the concentrations of certain metals (Al, Fe, Mn and Ni) in sediment, suggesting similar sources and/or similar geochemical processes controlling such metals. Higher concentrations of Cu, Zn and percent organic matter contents were found in the middle-inner bays sediments. Based on the correlation matrix obtained for metal data, organic matter was found to be the dominant factor controlling Cu and Zn distributions in the sediment. In general, mean Cu and Zn levels in the bay were above background concentrations in Mediterranean sediments. Zooplankton metal concentrations were similar to sediment distributions.     

Vegetative Growth,Yield and Leaf Mineral Composition in Strawberry (Fragaria × Ananassa DUCH. CV. Pajaro) as Influenced using Nickel Sulfate and Urea Sprays

In this study, interactions of nickel sulfate and urea sprays on vegetative growth, yield and leaf mineral contents in strawberry were investigated. Rooted Pajaro strawberry plants were potted in 3 liter pots filled with soil, leaf mold and sand (1:1:1, v/v/v). Established plants were foliar sprayed with nickel sulfate at 0, 150, 300 and 450 mg L^?1 and urea 0 and 2 g L^?1 concentrations. Results indicated that nickel (Ni; 300 mg L^?1) plus urea (2 g L^?1) significantly increased the yield and runner numbers. Nickel sulfate at the rate of 300 and 150 mg L^?1and urea (2 g L^?1) significantly increased the crown numbers. The greatest root fresh and dry weights were obtained from untreated plants. Urea at 2 g L^?1 without nickel significantly increased shoot fresh and dry weights. Nickel at 450 mg L^?1 without urea significantly increased Ni concentration in leaves. Overall, nickel sulfate at 150 and 300 mg L^?1 along with urea at 2 g L^?1 were the best treatments.     

INDUCTION OF OXIDATIVE STRESS AND ANTIOXIDANT ENZYMES BY EXCESS COBALT IN MUSTARD

This study focuses on induction of oxidative stress and antioxidative defense mechanism on exposure to excess cobalt (Co) in mustard (Brassica campestris L.; cv. ‘T-59’) plants grown in refined sand. Plants were grown for 40 days at normal (0.1 μM) Co. Additional cobalt was supplied from d 41 at 6 levels, i.e., 0.1 (control), 100, 200, 300, 400 and 500 μM as cobalt sulfate. The primary site of Co toxicity was shoots where middle leaves developed interveinal chlorosis after three days of excess cobalt supply (>100 μM). At severity these chlorotic spots became necrotic and affected areas appeared dry and papery, at this stage, growth of the plants were completely checked, the upper part of the stem became dry and hanged down. The toxicity of cobalt at d 46, i.e., six days after metal supply, (DAMS) reduced the dry weight, concentrations of chlorophyll a, b and carotenoids in leaves and tissue Fe with decreased activity of catalase and lipid peroxidation. Enhancement in proline concentration and elevated activities of antioxidant enzymes peroxidase, superoxide dismutase and ascorbate peroxidase were observed in leaves and roots in response to excess Co supply in mustard. Cobalt concentration of mustard in leaves and roots, ranged from 200 to 397 μg g^?1 at excess Co as compared to 1.1 to 2.5 μg Co g^?1 dry matter in control (0.1 μM Co).     

PHYTOTOXIC EFFECTS OF CADMIUM EXPOSURE AND METAL ACCUMULATION IN SUNFLOWER

The phytotoxicity imposed by cadmium (Cd) in sunflower was investigated on biomass, Cd accumulation, superoxide and lipid peroxidation product as well as the activities of superoxide dismutase, catalase and peroxidase. Plants accumulate substantial amount of Cd in different parts, the maximum being in roots, i.e., up to 820 μg g^?1 dry matter. Cadmium induced oxidative stress, indicated by increase in lipid peroxidation and superoxide content with increase in metal supply. Under Cd stress, the activities of superoxide dismutase and catalase declined to a greater extent in roots than in leaves. Even though the peroxidase activity increased in leaves, a decreasing trend was observed in root due to Cd stress. The threshold of toxicity (10% growth reduction) and toxicity (33% growth reduction) values of Cd in sunflower were 14 and 72 μg g^?1 in leaves, 19 and 90 μg g^?1 in stem and 65 and 250 μg g^?1 Cd in roots, respectively.     

Evaluation of Toxicity Level of Nickel on Growth,Photosynthetic Efficiency,Antioxidative Enzyme,and Its Accumulation in Cauliflower

A study was conducted to determine the toxicity level of nickel using cauliflower (Brassica oleracea L. var. botrytis) cv. Snowball grown in refined sand with complete nutrient solution for 79 days. At day 80, plants were separated into three lots. One lot was treated as the control (0.0001 mM Ni) while other two lots were supplied with excess nickel (Ni) at 0.1 and 0.5 mM. The toxicity symptoms of Ni appeared as chlorosis of young leaves. No curd was formed at 0.5 mM Ni supply. Excess Ni decreased biomass, chlorophyll, Hill reaction activity, and carbohydrate fraction, and enzyme activities of catalase, peroxidase, and acid phosphatase in leaves. Excess Ni increased concentration of starch, phenol, and nonprotein nitrogen and decreased protein nitrogen in leaves. Increase in Ni supply increased Ni concentration in all parts of cauliflower, whereas the concentration of phosphorus, sulfur, iron, and manganese decreased significantly.     

Molybdenum Stress Modulates Enzymes Responsive to Oxidative Stress and Affects Seeds Viability and Vigor in Chickpea

The importance of molybdenum (Mo) for plant growth is disproportionate with respect to the absolute amounts required by most plants. Chickpea (Cicer arietinum L.) cv. K-75 plants were raised in refined sand in glasshouse at graded levels from 0.002 to 1 µM for 100 days. Mo deficiency symptoms appeared as interveinal chlorosis of middle and old leaves. Compared with the control (0.2 µM Mo), dry matter, yield and seed protein decreased at low and excess Mo. The concentration of Mo in leaves and seed as well as the activity of nitrate reductase (NR) increased with an increase in Mo supply. The activities of antioxidative enzymes stimulate at both low and excess Mo supply. Low and excess Mo decreased the lipid peroxidation status in chickpea leaves, suggesting its antiperoxidative nature. The values of deficiency, threshold of deficiency and threshold of toxicity of Mo were, respectively, 0.38, 1.2 and 15 µg g^?1 in leaves of chickpea.     

Impact of Pseudomonads and Ethylene on the Cadmium and Nickel Rhizofiltration of Sunflower,Squash, and Indian Mustard

Three hydroponic experiments were set up to study the rhizofiltration of cadmium (Cd) or nickel (Ni) from artificially contaminated nutrient solution with sunflower, squash, or Indian mustard. After 48 h of exposure with 2 mg L^?1 Cd‐contaminated water, 460, 415, or 1092 µg Cd g^?1 (dry weight) was detected in roots of 33‐day‐old sunflower and squash or in 50‐day‐old Indian mustard, respectively. As calculated, 1 g of root dry matter of the tested crop species removed 5.7–12.4% of total Cd content present in the nutrient solution. It was supposed that pseudomonads (soil rhizoplane bacteria) and the plant growth hormone ethylene can enhance the specific surface of roots and hence roots' metal adsorption capacity. As a trend, pretreatment of Indian mustard with Pseudomonas fluorescens bacteria enhanced slightly the Cd (from 1793 to 2346 µg g^?1) or Ni (from 1088 to 1192 µg g^?1) concentration of roots. Cadmium concentration in roots was also enhanced from 2694 to 3273 µg g^?1 when the roots of Indian mustard were pretreated with Cd‐tolerant rather than Cd‐sensitive Pseudomonas cepacia. In spite of the occurrence of new root hairs, the pretreatment of roots with ethylene proved to be ineffective in enhancement of the Cd rhizofiltration capacity of Indian mustard.     

Effect of molybdenum stress on growth,yield and seed quality in black gram

Black gram (Vigna mungo L.) var. Shyam plants were raised in refined sand at four levels of molybdenum (Mo), i.e., low (0.002 µM) to excess (2 µM) for 70 days. The molybdenum deficiency symptoms appeared as interveinal chlorosis of young and middle leaves. Compared to control (0.2 µM Mo), total dry matter, seed yield and seed protein decreased at low and excess Mo. The concentration of Mo in leaves and seed as well as activity of nitrate reductase increased with an increase in Mo supply. Low and excess Mo deteriorated the quality of seeds by lowering the content of starch, sugars, protein, and nitrogen and increasing electrical conductivity of seed leachate. Molybdenum deficiency and excess both resulted in production of lightweight immature seeds, poor in vigor and germination potential. The values of sufficiency and threshold of toxicity in leaves were 0.078 and 2.15 µg Mo g^?1 dry matter of black gram.     

Effect of elevated concentrations of Cd and Zn in soil on spring wheat yield and the metal contents of the plants

The effect of increasing concentrations of Cd and Zn in a sandy soil on spring wheat (Triticum vulgare L.) yields and the metal contents of the plants was examined in a pot experiment to establish critical levels of these metals in soil. The metals were added (individually and jointly) to the soil as sulfates in the following doses (in μg g^?1, dry wt.): Cd — 2, 3, 5,10, 15, 25, and 50; Zn ?200, 300, 500, 1000, 1500, 2500, and 5000. Cadmium added to soil did not affect yields of wheat. The Zn dose of 1000 μg g^?1 strongly reduced crop yields; at 1500 μg g^? Zn dose wheat did not produce grain. The metal contents of wheat increased with increasing concentrations of Cd and Zn in soil up to 10.3 and 1587 μ g^? of Cd and Zn in straw, respectively. The concentrations of both metals were higher in straw than in grain by factors of 3–7 and 1.5–2 for Zn and Cd, respectively. The relationships between Cd and Zn contents of the plants and soils were best expressed by exponential equations. High concentrations of Zn in soils (1042 and 1542 μg g^?1) enhanced uptake of Cd by plants. The tested threshold concentrations of the metals in soils (3 μg g^?1 for Cd and 200–300 μg g^?1 for Zn) are safe for Zn but are too high for Cd in terms of protecting plants from excessive metal uptake. The critical Cd content of sandy soil should not exceed 1.5 μg g^?.     

The Physiology and Biochemical Tolerance of Cabbage to Se (VI) Addition to the Soil and by Foliar Spraying

The effects of selenium (Se) (VI) soil fertilization with 2 μg Se L^?1 or foliar spraying twice with 20 mg Se L^?1 in the form of sodium (Na) selenate on the physiological and biochemical characteristics of cabbage plants were studied. The ability of the plants to take up Se and translocate it to different parts of the plants was also studied. Despite the high concentration of Se in the foliar solution, there was no effect on photosynthesis, transpiration rate, photochemical efficiency of PSII, or electron transport system activity. The amount of chlorophyll and anthocyanins were unchanged. At harvest, the concentration of Se in control plants was lower than 100 ng Se g^?1 dry weight (DW), while plants treated with 20 mg Se L^?1 contained 5500 ng Se g^?1. Selenium enriched cabbage could be used in human nutrition. The tolerance of cabbage to Se could be explained by the formation of insoluble compounds that are not available for the plant.     

Hg, Cu, Pb, Cd, and Zn Accumulation in Macrophytes Growing in Tropical Wetlands

The concentrations of Hg, Cu, Pb, Cd, and Zn accumulated by regional macrophytes were investigated in three tropical wetlands in Colombia. The studied wetlands presented different degrees of metal contamination. Cu and Zn presented the highest concentrations in sediment. Metal accumulation by plants differed among species, sites, and tissues. Metals accumulated in macrophytes were mostly accumulated in root tissues, suggesting an exclusion strategy for metal tolerance. An exception was Hg, which was accumulated mainly in leaves. The ranges of mean metal concentrations were 0.035?C0.953 mg g^?1 Hg, 6.5?C250.3 mg g^?1 Cu, 0.059?C0.245 mg g^?1 Pb, 0.004?C0.066 mg g^?1 Cd, and 31.8?363.1 mg g^?1 Zn in roots and 0.033?C0.888 mg g^?1 Hg, 2.2?C70.7 mg g^?1 Cu, 0.005?C0.086 mg g^?1 Pb, 0.001?C0.03 mg g^?1 Cd, and 12.6?C140.4 mg g^?1 Zn in leaves. The scarce correlations registered between metal concentration in sediment and plant tissues indicate that metal concentrations in plants depend on several factors rather than on sediment concentration only. However, when Cu and Zn sediment concentrations increased, these metal concentrations in tissues also increased in Eichhornia crassipes, Ludwigia helminthorriza, and Polygonum punctatum. These species could be proposed as Cu and Zn phytoremediators. Even though macrophytes are important metal accumulators in wetlands, sediment is the main metal compartment due to the fact that its total mass is greater than the corresponding plant biomass in a given area.     

Bioremediation of Co-contamination of Crude Oil and Heavy Metals in Soil by Phytoremediation Using Chromolaena odorata (L) King & H.E. Robinson

The capability of Chromolaena odorata (L) to grow in the presence of different concentrations of three heavy metals in crude oil-contaminated soil and its capability to remediate the contaminated soil was investigated using pot experiments. C. odorata plants were transplanted into contaminated soil containing 50,000 mg kg^?1 crude oil and between 100 and 2,000 mg kg^?1 of cadmium, nickel, and zinc and watered weekly with water containing 5% NPK fertilizer for 180 days. C. odorata did not show any growth inhibition in 50,000 mg kg^?1 crude oil. Plants in experiments containing 2,000 mg kg^?1 Cd showed little adverse effect compared to those in Zn-treated soil. Plants in 1,000 and 2,000 mg kg^?1 Ni experiments showed more adverse effects. After 180 days, reduction in heavy metals were: 100 mg kg^?1 experiments, Zn (35%), Cd (33%), and Ni (23%); 500 mg kg^?1, Zn (37%), Cd (41%), and Ni (25%); 1,000 mg kg^?1, Zn (65%), Cd (55%), and Ni (44%); and 2,000 mg kg^?1, Zn (63%), Cd (62%), and Ni (47%). The results showed that the plants accumulated more of the Zn than Cd and Ni. Accumulation of Zn and Cd was highest in the 2,000 mg kg^?1 experiments and Ni in the 500 mg kg^?1 experiments. Crude oil was reduced by 82% in the experiments that did not contain heavy metals and by up to 80% in the heavy metal-treated soil. The control experiments showed a reduction of up to 47% in crude oil concentration, which was attributed to microbial action and natural attenuation. These results show that C. odorata (L) has the capability of thriving and phytoaccumulating heavy metals in contaminated soils while facilitating the removal of the contaminant crude oil. It also shows that the plant??s capability to mediate the removal of crude oil in contaminated soil is not significantly affected by the concentrations of metals in the soil.     

Impact of Acid Mine Drainage (AMD) on Water Quality, Stream Sediments and Periphytic Diatom Communities in the Surrounding Streams of Aljustrel Mining Area (Portugal)

Aljustrel mining area is located in the Iberian Pyrite Belt, one of the greatest concentrations of massive sulphide deposits that extends from Lousal (Portugal) to Aznalcóllar (Spain). The surrounding streams, Roxo, Água Azeda and Água Forte, are influenced by the erosion of the tailing deposits and the input of acid mine drainage (AMD) from the abandoned Aljustrel pyrite mines, recently reopened in 2007. The purpose of this study was to understand how these adverse conditions influenced the stream sediments, water quality and periphytic diatom communities and establish the pre-restoration local conditions to judge the success of rehabilitation program now under way. For stream sediments, the highest metal concentration samples were found at sites F, G and H. Arsenic, Cu, Fe, Pb and Sb detected concentrations, generally exceeded the probable effect concentration values reaching level 4: the highest toxicity level. In surficial water samples of AMD affected sites (F, G and H), low pH values (1.5 to 3.5) and high metal concentrations of As (6,837 μg L^?1), Cd (455 μg L^?1), Cu (68,795 μg L^?1), Fe (1,262,000 μg L^?1), Mn (19,451 μg L^?1), Pb (136 μg L^?1), and Zn (264,377 μg L^?1) were found. In these sites, the diversity index (H′) for diatoms was low (0.6 to 2.8) and the dominant taxa were Eunotia exigua (site F, 33.5%) and Pinnularia acoricola (abundances in sites: F, 86.8%; G, 88.5%; and H, 91.1%). In opposition, in less AMD impacted, H′ was high (1.5 to 4.6) and low metal concentrations and high pH were found. Achnanthidium minutissimum was the dominant taxon in (abundances in sites: A, 76.1% and B, 24.39%). Canonical correspondence analysis showed that spatial variation due to mine influence was more important than seasonal variation, which did not show any pattern.     

Mercury in Biota and Surficial Sediments from Coatzacoalcos Estuary, Gulf of Mexico: Distribution and Seasonal Variation

Variation of mercury (Hg) in sediments and biota from Coatzacoalcos estuary during the dry, rainy and windy seasons was estimated. In sediments, Hg concentrations ranged from 0.07 μg g^?1 in site 13 (Ixhuatepec) located upstream, to 1.06 μg g^?1 in site 3 (Coatzacoalcos river), located in the industrialized area. Highest enrichment factor (EF) and index of geoaccumulation (I _geo) in surficial sediments were 53 and 5.1 respectively. From EF and I _geo, it is considered that Coatzacoalcos estuary is from moderately contaminated to contaminated. In most fish species from Coatzacoalcos estuary, the sequence of Hg concentration was liver>muscle>gills. Average Hg concentrations in soft tissue of bivalves ranged from 0.09 μg g^?1 in Corbicula fluminea to 0.18 μg g^?1 in Polymesoda caroliniana. Biota-sediment accumulation factor (BSAF) ranged from 0.9 in P. caroliniana during the rainy season (site 4) to 3.8 in P. caroliniana from the same site during the windy season.     

Effects of microbial inoculations on soil chemical,biochemical and microbial biomass carbon of cassava (Manihot esculenta Crantz) growing Vertisols

Cassava is an important subsidiary food in the tropics. In Tamil Nadu, India, microbial cultures were used to eradicate the tuberous root rot of cassava. Hence, an experiment was conducted for two consecutive years to test the effects of coinoculation of microbes on soil properties. The surface soil from the experimental site was analysed for soil available nutrients, soil enzyme activities and microbial biomass carbon. The treatment of Azospirillum with Trichoderma at the 50% recommended N:P₂O₅:K₂O (NPK) rate (50:25:50 kg ha^?1) significantly increased soil available nitrogen (142.81 kg ha^?1) by 72.66% over uninoculated control. There was a significant increase in available phosphorus in soil by the inoculation of AM (arbuscular mycorrhizal) fungi with Trichoderma at the 50% recommended NPK rate (41.04 kg ha^?1) compared to other treatments. The application of Pseudomonas fluorescens with Trichoderma at the 50% recommended NPK rate significantly increased available iron (19.34 µg g^?1) in soil. The treatment of Azospirillum with Trichoderma increased urease enzyme activity at the recommended NPK rate (816.32 μg urea hydrolyzed g^?1 soil h^?1). Soil application of all cultures at the 50% recommended NPK rate significantly increased dehydrogenase activity (88.63 μg TPF g^?1 soil) and β-glucosidase activity (48.82 μg PNP g^?1 soil) in soil. Inoculation of Trichoderma alone at the 50% recommended NPK rate significantly increased microbial biomass carbon (3748.85 μg g^?1 soil). Thus, the microbial inoculations significantly increased soil available nutrient contents, enzyme activities such as urease, dehydrogenase and β-glucosidase activity and microbial biomass carbon by reducing the amount of the required fertilizer.     

Partitioning of Hg Between Solid and Dissolved Organic Matter in the Humus Layer of Boreal Forests

The mobility of mercury (Hg) deposited on soils controls the concentration and toxicity of Hg within soils and in nearby streams and lakes, but has rarely been quantified under field conditions. We studied the in situ partitioning of Hg in the organic top layer (mor) of podsols at two boreal forest sites differing in Hg deposition and climatic regime (S. and N. Sweden, with pollution declining to the north). Soil solution leaching from the mor layer was repeatedly sampled using zero-tension lysimeters over 2 years, partly in parallel with tension lysimeters. Concentrations of Hg and dissolved organic carbon (DOC) were higher while pH was lower at the southern site (means ± SD: Hg?=?44?±?15 ng L^?1, DOC?=?63.0?±?31.3 mg L^?1, pH?=?4.05?±?0.53) than at the northern site (Hg?=?22?±?6 ng L^?1, DOC?=?41.8?±?12.1 mg L^?1, pH?=?4.28?±?0.43). There was a positive correlation over time between dissolved Hg and DOC at both sites, even though the DOC concentration peaked during autumn at both sites, while the Hg concentration remained more constant. This correlation is consistent with the expected strong association of Hg with organic matter and supports the use of Hg/C ratios in assessments of Hg mobility. In the solid phase of the overlying O_f layer, both Hg concentrations and Hg/C ratios were higher at the southern site (means ± SD: 0.34?±?0.06 μg g^?1 dw and 0.76?±?0.14 μg g^?1 C, respectively) than at the northern site (0.31?±?0.05 μg g^?1 dw and 0.70?±?0.12 μg g^?1 C, respectively). However, concentrations in the solid phase differed less than might be expected from the difference in current atmospheric input, suggesting that the fraction of natural Hg is still substantial. At both sites, Hg/C ratios in the upper half of the mor layer were only about two thirds of those in the lower half, suggesting that the recent decrease in anthropogenic Hg deposition onto the soil is offset by a natural downward enrichment of Hg due to soil decomposition or other processes. Most interestingly, comparison with soil leachate showed that the average Hg/C ratios in the dissolved phase of the mor layers at both sites did not differ from the average Hg/C ratios in the overlying solid organic matter. These results indicate a simple mobilisation with negligible fractionation, despite differences in Hg deposition patterns, soil chemistry and climatic regimes. Such a straight-forward linkage between Hg and organic matter greatly facilitates the parameterisation of watershed models for assessing the biogeochemical fate, toxic effect and critical level of atmospheric Hg input to forest soils.     

Assessing a suitable extractant and critical limits of nickel in soil and plant for predicting the response of barley (Hordeum vulgare L.) to nickel grown in Inceptisols

ABSTRACT

Nickel (Ni) is an essential element for plants. Abundant information exists on Ni toxicity in soil–plant system but not much is available on its critical level of deficiency (CLD) in soils and plants. Five chemical extractants were evaluated to find a suitable extractant for Ni in Inceptisol. Twenty-one soils having low to high levels of Ni were used to grow barley (Hordeum vulgare L). The amount of Ni extracted was correlated with Ni concentration and uptake by barley. The diethylene triamine penta acetic acid-calcium chloride (0.005 M DTPA-CaC1₂) was identified as the most promising soil extractant for Ni. The CLD of Ni for 0.005 M DTPA-CaC1₂ in soil was 0.22 mg kg^?1 whereas in barley plant it was 2.14 mg kg^?1. Application of 7.5 mg kg^?1 Ni in soil caused a significant increase in Ni concentration in the shoot of barley in all the soils irrespective of the initial Ni status.     

Remediation of a Sandy Soil Contaminated with Cadmium,Nickel, and Zinc using an Insoluble Polyacrylate Polymer

Abstract

This study was carried out to investigate whether an insoluble polyacrylate polymer could be used to remediate a sandy soil contaminated with cadmium (Cd) (30 and 60 mg Cd kg^?1 of soil), nickel (Ni) (50 and 100 mg Ni kg^?1 of soil), zinc (Zn) (250 and 400 mg Zn kg^?1 of soil), or the three elements together (30 mg Cd, 50 mg Ni, and 250 mg Zn kg^?1 of soil). Growth of perennial ryegrass was stimulated in the polymer‐amended soil contaminated with the greatest amounts of Ni or Zn, and when the three metals were present, compared with the unamended soil with the same levels of contamination. Shoots of plants cultivated in the amended soil had concentrations of the metals that were 24–67% of those in plants from the unamended contaminated soil. After ryegrass had been growing for 87 days, the amounts of water‐extractable metals present in the amended soil varied from 8 to 53% of those in the unamended soil. The results are consistent with soil remediation being achieved through removal of the metals from soil solution.     

Effect of 7-year application of a nitrification inhibitor, dicyandiamide (DCD), on soil microbial biomass, protease and deaminase activities, and the abundance of bacteria and archaea in pasture soils

Purpose

The nitrification inhibitor dicyandiamide (DCD) has been shown to be highly effective in reducing nitrate (NO₃ ^?) leaching and nitrous oxide (N₂O) emissions when used to treat grazed pasture soils. However, there have been few studies on the possible effects of long-term DCD use on other soil enzyme activities or the abundance of the general soil microbial communities. The objective of this study was to determine possible effects of long-term DCD use on key soil enzyme activities involved in the nitrogen (N) cycle and the abundance of bacteria and archaea in grazed pasture soils.

Materials and methods

Three field sites used for this study had been treated with DCD for 7 years in field plot experiments. The three pasture soils from three different regions across New Zealand were Pukemutu silt loam in Southland in the southern South Island, Horotiu silt loam in the Waikato in the central North Island and Templeton silt loam in Canterbury in the central South Island. Control and DCD-treated plots were sampled to analyse soil pH, microbial biomass C and N, protease and deaminase activity, and the abundance of bacteria and archaea.

Results and discussion

The three soils varied significantly in the microbial biomass C (858 to 542 μg C g^?1 soil) and biomass N (63 to 28 μg N g^?1), protease (361 to 694 μg tyrosine g^?1 soil h^?1) and deaminase (4.3 to 5.6 μg NH₄ ⁺ g^?1 soil h^?1) activity, and bacteria (bacterial 16S rRNA gene copy number: 1.64?×?10⁹ to 2.77?×?10⁹ g^?1 soil) and archaea (archaeal 16S rRNA gene copy number: 2.67?×?10⁷ to 3.01?×?10⁸ g^?1 soil) abundance. However, 7 years of DCD use did not significantly affect these microbial population abundance and enzymatic activities. Soil pH values were also not significantly affected by the long-term DCD use.

Conclusions

These results support the hypothesis that DCD is a specific enzyme inhibitor for ammonia oxidation and does not affect other non-target microbial and enzyme activities. The DCD nitrification inhibitor technology, therefore, appears to be an effective mitigation technology for nitrate leaching and nitrous oxide emissions in grazed pasture soils with no adverse impacts on the abundance of bacteria and archaea and key enzyme activities.