Browsing by Author "Jeyakumar, Paramsothy"
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- ItemCopper and zinc dynamics and bioavailability in soils amended with biosolids : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University, Palmerston North, New Zealand(Massey University, 2010) Jeyakumar, ParamsothyGlobal sewage sludge (biosolids) production is increasing as a result of rapidly growing human population and ensuing industrial activities. Land application of this waste is becoming a serious environmental issue because the high levels of heavy metals in biosolids can upset soil microbial activity and nutrient balance when the waste is added to forest or agricultural lands. It is widely accepted that bioavailability, rather than total soil concentration, is more important when assessing the risk associated with metal contamination. The bioavailability of a heavy metal is dependent on the chemical nature of the metal, the chemical, physical and biological properties of biosolids that contain the metal and of soil that receives the biosolids. It also depends on the interaction of the biosolids with soil, plants and soil microorganisms. The overall aim of this thesis was to assess the bioavailability of biosolids–derived Cu and Zn and the comparative effects of these metals on plant and soil microbial activity, with special attention to mycorrhiza, and the effects of application of lime and Al dross as ameliorants for the reduction of bioavailability of these two metals. Biosolids were collected from the Palmerston North City Council Waste Water Treatment Plant (PNCCWTP) sludge lagoon in Palmerston North, New Zealand. Because the metal concentrations were low, for research purposes these biosolids were spiked separately with three levels of Cu (to give final concentrations of 50, 150 and 250 mg/kg soil) and Zn (to give final concentrations of 150, 450 and 750 mg/kg soil) added as metal sulphate salts. The biosolids were anaerobically incubated, and it was found that a shorter period of equilibration (2 months) than the previously used 6–9 months was sufficient for Cu and Zn to be fully incorporated into the biosolids matrix. As biosolids in New Zealand are currently applied to forest lands, two important forest plants, poplar and pine, were considered for the study in this thesis. The effects of elevated concentrations of Cu and Zn in a soil amended with metal spiked biosolids on poplar plants were investigated in a 147 day glasshouse pot trial. The findings of this trial showed that at the same total soil metal concentration, biosolids–derived Cu was more toxic than Zn to soil microorganisms, whereas Zn was more toxic to poplar and ECM fungi. In a similar glasshouse study lasting 312 days with pine, Cu did not show a phytotoxic effect, but Zn was phytotoxic to pine. However, both metals were toxic to microorganisms and neither metal influenced ECM fungi colony development. The currently recommended maximum metal concentration limits for New Zealand soils of 100 mg/kg for Cu and 300 mg/kg for Zn appear to be high for both metals with respect to soil microbial activity, but low for Cu and high for Zn with respect to poplar and pine growth. A laboratory incubation trial with Cu– and Zn– spiked biosolids added to eight soils representing the major Soil Groups collected from across the North Island of New Zealand (biosolids added to give final soil concentrations of 150 mg/kg for Zn or 450 mg/kg for Cu), showed that crystalline Fe oxide was the dominant factor explaining 90% of the variability in exchangeable Cu. For Zn, clay content and pH were the controlling soil factors that together explained 73% of the variability in exchangeable Zn. An increased content of crystalline Fe oxide increased the soil exchangeable Cu concentration. Decreasing pH and increasing clay content increased the soil exchangeable Zn concentration. The effect of lime (0.1 and 0.5%), Al dross (2 and 6%) and a combination of lime and Al dross (0.1% lime+2% Al dross) as soil amendments for the amelioration of the toxic effect of biosolids–derived Cu (144 mg/kg in soil) and Zn (417 mg/kg in soil) on microorganisms and poplar were also studied. Results revealed that application of lime and Al dross (pH 10) as a mixture (0.1% lime+2% Al dross) was able to ameliorate Cu and Zn phytotoxicity, and significantly increase the DM yield of poplar, ECM fungi population and microbial activity in the Cu and Zn contaminated soils. The findings of the studies in this thesis are applicable to environmental regulations with respect to heavy metal limits that seek to protect agricultural and forest land, human and animal health, and soil and drinking water quality, in scenarios where biosolids are applied to soil.
- ItemManipulating soil bioavailable copper as an innovative nitrate leaching mitigating strategy in New Zealand pastoral soils : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Soil Science, School of Agriculture and Environment, College of Sciences, Massey University, Palmerston North, New Zealand(Massey University, 2023) Matse, Dumsane ThembaUrine patches are the primary sources of nitrate (NO₃⁻ -N) leaching from pastoral dairy farms. Since NO₃⁻ -N is the product of nitrification, a clear understanding of the nitrification process is a vital step toward the development of effective and efficient mitigation approaches. The first step of ammonia (NH₄⁺) oxidation to hydroxylamine (NH₂OH) is catalyzed by the ammonia monooxygenase enzyme (AMO), and copper (Cu) is a co-factor in the activity of the AMO enzyme. Therefore, manipulating Cu bioavailability through the application of Cu-complexing organic compounds such as calcium lignosulphonate (LS) and co-poly acrylic-maleic acid (PA-MA) to soil could influence AMO activity and consequently limit the nitrification rate in soil. There are no published studies that have examined the effect of bioavailable Cu concentration changes on nitrification rate, ammonia-oxidizing bacteria (AOB) and archaea (AOA), and NO₃⁻ -N leaching. The overall aim of this thesis is to determine the significance of bioavailable Cu in the nitrification process in the context of developing novel Cu-complexing organic compounds to inhibit nitrification rate in pastoral soils. A soil incubation study was conducted to characterize the relationship between changes in soil bioavailable Cu concentration and nitrification rate. This study was conducted using three pastoral soils (Pumice, Pallic, and Recent soils) spiked with five Cu levels (0.1, 0.3, 0.5, 1, and 3 mg kg⁻¹). Treatments of Cu-complexing compounds were separately applied to each Cu level. The treatments were urea applied at 300 mg N kg⁻¹, urea + LS at 120 mg kg⁻¹, and urea + PA-MA at 10 mg kg⁻¹. Results show that increasing the added Cu concentration from 0.1 to 3 mg kg⁻¹ increased nitrification rate by 35, 22, and 33% in the Pumice, Pallic, and Recent soils, respectively. Application of LS and PA-MA significantly (P ˂ 0.05) decreased nitrification rate with the mean reduction being 59 and 56%, 32 and 26%, and 39 and 38% in the Pumice, Pallic, and Recent soils, respectively at Day 8 relative to the urea-only treatment. To further extend knowledge of the relationship between bioavailable Cu and the key nitrifying microorganisms in soils, a greenhouse-based pot trial using three soils (Pumice, Pallic, and Recent soils) planted with ryegrass and treated with synthetic urine applied at 300 kg N ha⁻¹ and three levels of Cu (0, 1, 10, 100 mg added Cu kg⁻¹) was established. Results show that AOB amoA gene abundance increased as a function of increasing added Cu from 1 to 10 mg kg⁻¹ but was inhibited at 100 mg added Cu kg⁻¹ in both Pallic and Recent soils. The effect of bioavailable Cu was not apparent in the Pumice soil. The increase in AOB amoA gene abundance positively correlated with nitrification rate in both the Pallic (r = 0.982, P < 0.01) and Recent soil (r = 0.943, P < 0.01) but not in the Pumice soil. There was no effect of increasing Cu concentration on AOA amoA gene abundance in all three soils. Results from both incubation and greenhouse pot trials provide strong evidence that Cu is an important trace element in the nitrification process and reducing Cu can reduce nitrification in soil. However, in order to definitively quantify this treatment effect, further field studies were necessary. Therefore, a field lysimeter study was conducted using Pumice soil (Manawatu climate) and Pallic soil (Canterbury climate). The following treatments were investigated to reduce NO₃⁻ -N leaching during late-autumn application; urine only at 600 kg N ha⁻¹, urine + PA-MA at 10 kg ha⁻¹, urine + LS at 120 kg ha⁻¹, urine + a split-application of calcium lignosulphonate (2LS at same rate, initial and after a month of first application), and urine + ProGibb SG (GA at 80 g ha⁻¹) + LS (GA + LS). Another set of treatment applications, urine only, urine + GA only, and urine + GA + LS, were applied mid-winter to both soils. The GA was applied to improve the effectiveness of these organic compounds during climatic periods of poor plant growth. Results showed that there was no significant reduction in mineral N leaching associated with the late-autumn application of both PA-MA and LS for the Pumice or Pallic soils. However, the application of 2LS reduced mineral N leaching by 16 and 11% in Pumice and Pallic soils, respectively, relative to urine-only. The late-autumn inclusion of GA increased the effectiveness of LS in both soils. This was confirmed by a significant reduction of mineral N leaching by 35% from both Pumice and Pallic soils. Mid-winter application of GA + LS significantly reduced mineral N leaching only in the Pumice soil (by 20%) but not in the Pallic soil relative to urine-only. In both late-autumn and mid-winter treatments application of the different Cu-complexing treatments did not have negative effects on pasture dry matter yield in either Pumice or Pallic soils. In this lysimeter study, the mechanistic effect of PA-MA and LS on reducing bioavailable, nitrification rate and AOB/AOA amoA gene abundance was not investigated. A second field lysimeter experiment was established using the Recent soil in Manawatu to explore the mechanism of Cu manipulation through the application of LS and PA-MA on nitrification rate, AOB/AOA amoA gene abundance, and mineral N leaching. The effect of combining organic inhibitors with GA on reducing mineral N leaching was also investigated. This study evaluated the same treatments used in the first lysimeter study and applications were again conducted at two different seasonal periods (late-autumn and mid-winter). The results showed that the effect of PA-MA and 2LS on bioavailable Cu corresponded with a reduction in nitrification rate and AOB amoA gene abundance. The effect of PA-MA and 2LS was associated with reduced mineral N leaching by values of 16 and 30%, respectively, relative to urine-only. The reduction in mineral N leaching induced by PA-MA and 2LS increased N uptake by 25 and 7.8% and herbage DM yield by factors of 11 and 8%, respectively, relative to the urine-only. The LS treatment did not induce a significant change of either bioavailable Cu or nitrification rate which corresponded to no significant effect on mineral N leaching. The late-autumn combination of GA + LS reduced mineral N leaching by 19% relative to urine-only, but there was no significant difference in mineral N leaching observed for the mid-winter application relative to urine-only. The overall results of this research show that bioavailable Cu is a vital trace element in the nitrification process and for AOB functioning in soil. Therefore, reduction in bioavailable Cu through the application of Cu-complexing compounds can inhibit nitrification. In this doctoral study, the application of Cu-complexing compounds (LS and PA-MA) showed potential to inhibit nitrification rate and subsequently reduce mineral N leaching in pastoral systems, but their efficacy depends on soil characteristics. Future work is recommended to investigate the effect of LS and PA-MA application on nitrous oxide emissions. Further research is recommended to investigate the short and long terms effects of these treatments on non-target soil microbiota.
- ItemPlant associated soil mechanisms of cadmium uptake and translocation in chicory and plantain : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Environmental Science at Massey University, Palmerston North, New Zealand(Massey University, 2021) Ubeynarayana, NilushaCadmium (Cd) is a non-essential trace element that is extensively distributed in the environment. Cadmium is effectively absorbed by plant roots and transported to its aerial parts and plants growing in soils with high Cd concentration can accumulate Cd in their roots and shoots to levels which can threaten human and animal health. Elevated Cd concentrations in New Zealand agricultural soils are a function of the country’s long-term history of using Cd-contaminated phosphate fertiliser. Recent studies have identified that two forage species chicory (Cichorium intybus L.) and plantain (Plantago lanceolata L.), which are increasingly used in New Zealand agriculture, accumulate a significantly higher shoot Cd concentration than traditional pasture species. The variation in Cd accumulation between forage species suggests that different plants have different abilities to absorb Cd in roots and translocate this trace element from roots to shoots. Thus, Cd uptake and the potential translocation of Cd to aerial tissues deserves more research, particularly for forage species of economic importance to countries such as New Zealand, where agriculture is dependent on pastoral grazing systems. Information from such studies will be useful in mitigating the continuing risk of Cd transfer into the food chain. The overall aim of this thesis is to better understand Cd uptake and translocation mechanisms in chicory and plantain. Cadmium uptake by plant roots is a function of rhizosphere soil chemistry and the interaction between plant roots and soil solution. Plants exude Low Molecular Weight Organic Acids (LMWOA) into soil solution and these play a key role in regulating Cd bioavailability. A pot trial was conducted to evaluate the influence of increasing soil Cd concentration on the secretion of LMWOAs by chicory and plantain roots and to analyse their impact on plant Cd uptake. Chicory and plantain were grown under increasing Cd levels and showed variable secretion of oxalic, fumaric, malic and acetic acids as a function of Cd treatment. Results revealed that the primary cause for the significant increase of shoot and root Cd concentration in both chicory and plantain, as a function of treatment level, is the significantly greater bioavailable Cd concentration in soil solution with increasing Cd treatment level. The significantly higher shoot Cd accumulation in chicory (18.63 mg Cd/kg DW) than plantain (4.22 mg Cd/kg DW) at the highest tested soil Cd concentration (1.6 mg Cd/kg) can be explained by increased acetic acid and reduced fumaric acid excretion from chicory relative to plantain. Increased understanding of Cd translocation mechanisms in plants requires knowledge of the free Cd2+ ion concentration in xylem saps. However, the determination of low concentrations of free Cd2+ ions in a low volume of xylem sap poses an analytical challenge. To overcome this limitation, a thiosalicylic-acid-modified carbon-paste electrode was developed as an alternative and reliable measurement tool for the detection of free Cd2+ ions in environmental samples, including xylem saps. Compared to other Cd2+ ion ligands used to develop Cd2+-ion-specific electrodes in literature, thiosalicylic acid is a readily available solid, which is stable to air, making it a conveniently handled ligand. The developed electrode showed a lower detection limit of 11 μg Cd/L (0.1 10-6 mol Cd/L) with a linear range from 20 to 100 μg Cd/L (0.18 10-6 to 0.88 10-6 mol Cd/L). To the best of my knowledge, this is the first time a Cd2+ ion-specific electrode was developed to determine free Cd2+ ion concentration in plant xylem sap. The modified electrode has the ability to distinguish between total Cd and free Cd2+ in solution and measure only the free Cd2+ ions in environmental samples, including xylem sap, with high precision (RSD<5%). Subsequent analysis using the thiosalicylic acid modified electrode showed that Cd is mainly in a complex form in chicory and plantain xylem sap. Therefore, a glasshouse experiment was set up with six increasing Cd concentrations in hydroponic solution to assess the impact of LMWOA on xylem sap Cd translocation and shoot accumulation in chicory and plantain. Results revealed that both chicory and plantain showed variable production of oxalic, fumaric, citric, malic and acetic acids with increasing Cd concentration in the hydroponic media. The higher shoot Cd accumulation (by 28-208%) in chicory compared to plantain can be explained in terms of variations in LMWOA production between chicory and plantain. Functional relationship analysis showed that the primary cause for higher shoot Cd concentration in chicory relative to plantain is fumaric acid production in chicory xylem sap which may bind with Cd in chicory and translocate the metal towards shoots. To explore the specific role of fumaric and acetic acids on Cd uptake and translocation in chicory, a glasshouse experiment was conducted with the external addition of fumaric and acetic acid into the hydroponic solution. Increasing fumaric acid concentration in the hydroponic solution showed the ability to reduce Cd uptake and translocation in chicory with a maximum reduction achieved at 10 mg/L and 50 mg/L fumaric acid treatment for root and shoot Cd accumulation, (respectively) for a solution concentration of 1 mg/L Cd. The shoot Cd concentration significantly increased at lower acetic acid treatment levels (1 mg/L) and reduced with increasing acetic acid concentrations from 10 mg/L to 50 mg/L in the presence of 1 mg Cd/L solution concentration. However, the root Cd accumulation increased as a function of acetic acid concentration in the hydroponic solution up to 50 mg/L acetic acid treatment. The root: shoot Cd concentration ratio showed a significant positive correlation (R=0.729 P<0.05) with acetic acid treatments (up to 50 mg/L treatment). Chicory biomass significantly reduced at all LMWOA treatments compared to the control treatment in the presence of 1 mg Cd/L Cd level, showing that there was a limited potential ameliorative effect of LMWOA on Cd toxicity at any concentration for the experimental conditions used in this study. This study highlights that variations in plant root LMWOA secretion and xylem sap LMWOA production between chicory and plantain can explain the different shoot Cd accumulation characteristics of these two forage species. This work shows that fumaric acid plays a fundamental role in both Cd uptake and translocation in chicory, while such a role is not clear for plantain. Low secretion of fumaric acid by roots and production of fumaric acid in chicory xylem sap aid to increase shoot Cd accumulation in chicory compared to plantain while low acetic acid secretion by chicory roots supports the high shoot Cd accumulation in chicory compared to plantain. Future work is recommended to develop a new cultivar of chicory which express traits of variations in fumaric acid production and acetic acid production. Such work may yield new cultivars of chicory which restrict the translocation of Cd from roots to shoots in this important forage species. The future application of this work is to help develop strategies which could assist in mitigating high Cd accumulation in offal to maintain the standards of New Zealand’s food production.