Muhammad Sabir

Contrasting effects of biochar, compost and farm manure on alleviation of nickel toxicity in maize (Zea mays L.) in relation to plant growth, photosynthesis and metal uptake

Nickel (Ni) toxicity in agricultural crops is a widespread problem while little is known about the role of biochar (BC) and other organic amendments like farm manure (FM) from cattle farm and compost (Cmp) on its alleviation. A greenhouse experiment was conducted to evaluate the effects of BC, Cmp and FM on physiological and biochemical characteristics of maize (Zea mays L.) under Ni stress. Maize was grown in Ni spiked soil without and with two rates of the amendments (equivalent to 1% and 2% organic carbon, OC) applied separately to the soil. After harvest, plant height, root length, dry weight, chlorophyll contents, gas exchange characteristics and trace elements in plants were determined. In addition, post-harvest soil characteristics like pHs, ECe and bioavailable Ni were also determined. Compared to the control, all of the amendments increased plant height, root length, shoot and root dry weight with the maximum increase in all parameters by FM (2% OC) treatment. Similarly, total chlorophyll contents and gas exchange characteristics significantly increased with the application of amendments being maximum with FM (2% OC) application. Amendments significantly increased copper, zinc, manganese and iron concentrations and decreased Ni concentrations in the plants. The highest reduction in shoot Ni concentration was recorded with FM (2% OC) followed by BC (2% OC) being 73.2% and 61.1% lower compared to the control, respectively. The maximum increase in soil pH and decrease in AB-DTPA extractable Ni was recorded with BC (2% OC) followed by FM (2% OC). It is concluded that FM (2% OC) was the most effective in reducing Ni toxicity to plants by reducing Ni uptake while BC (2% OC) was the most effective in decreasing bioavailable Ni in the soil through increasing soil pH. However, long-term field studies are needed to evaluate the effects of these amendments in reducing Ni toxicity in plants.

Mechanisms of metal-phosphates formation in the rhizosphere soils of pea and tomato: environmental and sanitary consequences

PurposeAt the global scale, soil contamination with persistent metals such as lead (Pb), zinc (Zn), and copper (Cu) induces a serious threat of entering the human food chain. In the recent past, different natural and synthetic compounds have been used to immobilize metals in soil environments. However, the mechanisms involved in amendment-induced immobilization of metals in soil remained unclear. The objective of the present work was therefore to determine the mechanisms involved in metal-phosphates formation in the rhizospheric soils of pea and tomato currently cultivated in kitchen gardens.Materials and methodsPea and tomato were cultivated on a soil polluted by past industrial activities with Pb and Zn under two kinds of phosphate (P) amendments: (1) solid hydroxyapatite and (2) KH2PO4. The nature and quantities of metal-P formed in the rhizospheric soils were studied by using the selective chemical extractions and employing the combination of X-ray fluorescence micro-spectroscopy, scanning electron microscopy, and electron microprobe methods. Moreover, the influence of soil pH and organic acids excreted by plant roots on metal-P complexes formation was studied.Results and discussionOur results demonstrated that P amendments have no effect on metal-P complex formation in the absence of plants. But, in the presence of plants, P amendments cause Pb and Zn immobilization by forming metal-P complexes. Higher amounts of metal-P were formed in the pea rhizosphere compared to the tomato rhizosphere and in the case of soluble P compared to the solid amendment. The increase in soil-metal contact time enhanced metal-P formation.ConclusionsThe different forms of metal-P formed for the different plants under two kinds of P amendments indicate that several mechanisms are involved in metal immobilization. Metal-P complex formation in the contaminated soil depends on the type of P amendment added, duration of soil-plant contact, type of plant species, and excretion of organic acids by the plant roots in the rhizosphere.

Chemically enhanced phytoextraction of Pb by wheat in texturally different soils

A pot study was used to examine the effects of amendments such as EDTA and elemental sulfur on the growth potential, gas exchange features, uptake and mobilization of Pb by wheat (Triticum aestivum L.) in two texturally different contaminated soils at three levels of EDTA (2, 4, 8 mmol kg(-1) dry soil) and two levels of elemental sulfur (100, 200 mmol kg(-1) dry soil). EDTA resulted in more solubilization of Pb than elemental sulfur in both soils. Application of EDTA and elemental sulfur increased shoot dry matter in the loamy sand soil, whereas in the sandy clay loam soil EDTA treated plants produced lower shoot dry matter compared to that observed with elemental sulfur. Application of EDTA 10d prior to harvest increased the amount of Pb accumulated into wheat shoots with more Pb accumulated by plants from the loamy sand than from the sandy clay loam soil. However, evaluation of the relative extraction efficiency expressed as the percentage of solubilized Pb that is subsequently also effectively accumulated by the plant shoots reveals that the relatively low efficiency does not warrant the massive mobilization induced by the environmentally persistent EDTA chelator. More modest mobilization of Pb induced by elemental sulfur and the higher relative extraction of mobilized Pb therefore deserves further attention in future research. In particular, attention needs to be paid to determining soil types in which elemental sulfur can induce significant impact on soil pH and metal mobility after application of a practically realistic dosage.

Organic and Inorganic Amendments Affect Soil Concentration and Accumulation of Cadmium and Lead in Wheat in Calcareous Alkaline Soils

Irrigation with untreated effluent in periurban agriculture could result in accumulation and bioconcentrations of cadmium (Cd) and lead (Pb). Different amendments were used to investigate their effect on availability, concentration, and uptake of metals by wheat in texturally different soils. Crop was irrigated with water containing Cd and Pb at 20 mg L−1, thereby adding 260 mg pot−1 of each metal. Amendments included calcium carbonate at 6 or 12%, gypsum at 50 or 100% of the soil gypsum requirement, farm manure at 7.50 or 15.00 g kg−1 soil, and a control. Amendments decreased ammonium bicarbonate diethylenetriaminepentaacetic acid (AB-DTPA)–extractable Cd and Pb concentrations and uptake by wheat. Dry matter, concentration, uptake, and extractability of Cd and Pb were greater in sandy loam soil compared with those in sandy clay loam soil irrespective of amendments. Sequential extraction showed that more metals were extracted from the control in all fractions and that predominantly metals were found in the carbonate fraction.

Heavy Metal Stress and Crop Productivity

Heavy metal contamination of the environment through anthropogenic activities and/or natural processes is a widespread and serious problem. Heavy metals occur in various forms in soil, which differ greatly with respect to their solubility/bioavailability. The geochemical behavior of heavy metals in soil, their uptake by plants, and effect on crop productivity is affected by various physicochemical properties of soil. Heavy metals mainly accumulate in root cells, due to their blockage by Casparian strips or due to trapping by the cell walls of roots. Excessive heavy metal accumulation in plant tissue impairs either directly or indirectly several biochemical, physiological, and morphological functions in plants and in turns interferes with crop productivity. Heavy metals reduce crop productivity by inducing deleterious effects to various physiological processes in plants including: seed germination, accumulation and remobilization of seed reserves during germination, plant growth, and photosynthesis. At the cellular level, heavy metal toxicity reduces crop productivity by producing reactive oxygen species, disturbing the redox balance and causing oxidative stress. Under heavy metal stress, plants have numerous defense mechanisms to manage heavy metal toxicity and to maintain their productivity, which include reduced heavy metal uptake by plants, sequestration into vacuoles, binding by phytochelatins, and activation of various antioxidants. This chapter presents the effect of heavy metals on physiological reactions in the plants’ crop productivity.

Phytoremediation: Mechanisms and Adaptations

Metal contamination of soils is ubiquitous around the globe. Metals accumulate in the soils to toxic levels that may lead to accumulation of metals in plants to unacceptable levels. Metal accumulation is a subject of serious concern due to the threat to plant growth, soil quality, animal and human health. Cleaning up of the soils to remove metals is a current necessity, but it is a challenging task. Different technologies being used nowadays are ex situ which ensues in destruction of soil structure thus leaving it non-useable with poor vegetative cover. Growing plants to clean up the soils is a cost-effective and environmentally friendly alternative. Phytoremediation seems attractive due to non-invasive and non-destructive technology which leaves the soil intact and biologically productive. Plants use different adaptive mechanisms to accumulate or exclude metals, thus maintaining their growth. Accumulation and tolerance of metals by the plants is a complex phenomenon. Movement of metals across the root membrane, loading and translocation of metals through the xylem and sequestration and detoxification of metals at cellular and whole plant levels are important mechanisms adopted by accumulator plants. Understanding the mechanism involved in phytoremediation is necessary to effectively use this technique for metal-contaminated soils. This chapter discusses different mechanisms adopted by plants for remediation of metal-contaminated soils.

CATEGORIZATION OF BRASSICA CULTIVARS FOR PHOSPHORUS ACQUISITION FROM PHOSPHATE ROCK ON BASIS OF GROWTH AND IONIC PARAMETERS

We categorized sixteen Brassica cultivars for their differential growth response and phosphorus (P) acquisition from phosphate rock (PR) and monoammonium phosphate (MAP). Plants were grown with both P sources in a nutrient solution experiment for 40 days. Cultivars differed significantly (P < 0.01) both for absolute as well as relative values of growth and physiological parameters at both P sources. Phosphorus deficiency in PR treatment significantly depressed biomass production (more than 2.5 times than control) and P concentration (about 1.5 times) in all of the cultivars. ‘Rainbow’ and ‘Poorbi Raya’ produced significantly more relative biomass than other cultivars grown with PR. Cultivars were classified into three classes on the basis of mean values of different parameters and their standard deviation viz low, medium and high. Cultivars were also classified into different classes while regressing biomass and P contents. Cultivars ‘Rainbow’ and ‘Poorbi Raya’ accumulated maximum shoot dry matter (1.21 and 1.27 g dry matter/plant, respectively) grown with phosphate rock, hence were categorized as high biomass producers. Cultivars ‘Rainbow’, ‘KS-74’, and ‘Poorbi Raya’ accumulated maximum P (5.58, 5.24, and 4.81 mg P plant−1, respectively) from PR and were categorized as high P accumulators. Cultivars with high biomass and high P contents such as ‘Rainbow’ and ‘Poorbi Raya’ at low available P (Rock P) would be used in further screening experiments to improve P efficiency in Brassica.

Contrasting Effects of Farmyard Manure (FYM) and Compost for Remediation of Metal Contaminated Soil

We investigated effect of farm yard manure (FYM) and compost applied to metal contaminated soil at rate of 1% (FYM-1, compost-1), 2% (FYM-2, compost-2), and 3% (FYM-3, compost-3). FYM significantly (P < 0.001) increased dry weights of shoots and roots while compost increased root dry weight compared to control. Amendments significantly increased nickel (Ni) in shoots and roots of maize except compost applied at 1%. FYM-3 and -1 caused maximum Ni in shoots (11.42 mg kg−1) and roots (80.92 mg kg−1), respectively while compost-2 caused maximum Ni (14.08 mg kg−1) and (163.87 mg kg−1) in shoots and roots, respectively. Plants grown in pots amended with FYM-2 and compost-1 contained minimum Cu (30.12 and 30.11 mg kg−1) in shoots, respectively. FYM-2 and compost-2 caused minimum zinc (Zn) (59.08 and 66.0 mg kg−1) in maize shoots, respectively. FYM-2 caused minimum Mn in maize shoots while compost increased Mn in shoots and roots compared to control. FYM and compost increased the ammonium bicarbonate diethylene triamine penta acetic acid (AB-DTPA) extractable Ni and Mn in the soil and decreased Cu and Zn. Lower remediation factors for all metals with compost indicated that compost was effective to stabilize the metals in soil compared to FYM.

VARIATION IN PHOSPHORUS EFFICIENCY AMONG BRASSICA CULTIVARS I: INTERNAL UTILIZATION AND PHOSPHORUS REMOBILIZATION

Plants have adapted a number of mechanisms to cope with widespread phosphorus (P) deficiency in arable lands. Crop species and even cultivars differ widely in one or more of these adaptive mechanisms hence, in P efficiency. Identification of these mechanisms is pre-requisite for long term breeding programs. Two independent experiments were conducted to study the possible mechanisms of P efficiency in Brassica cultivars. Eight Brassica cultivars (‘B.S.A.’, ‘Toria’, ‘Toria Selection’, ‘Brown Raya’, ‘Peela Raya’, ‘Dunkeld’, ‘Rainbow’, and ‘CON-1’) were selected on the basis of differences in growth under P deficiency from preliminary experiment. In the first experiment, cultivars were grown for 40 days in sand supplied either with sparingly soluble phosphate rock (PR) or soluble mono-ammonium phosphate (MAP). Cultivars differed significantly (P<0.05) for biomass production, P contents and P use efficiency. Low P availability in PR treatment resulted in significantly lower dry weights and P contents than those grown with MAP. The cultivars ‘Rainbow’, ‘Brown Raya’ and ‘Dunkeld’ accumulated more biomass (3.2 g/pot) and P contents (3.0 mg/pot) than other cultivars when grown with PR. Root dry weight was significantly correlated with shoot dry weight, shoot P content and total P content (r > 0.65) indicating significance of improved root growth for P acquisition. While in the second experiment cultivars were grown with adequate P for 30 days and then P was withdrawn from the nutrient solution by replacing fresh P free nutrient solution for 10 days. Induced P deficiency increased P contents in young leaves by two folds indicating remobilization of P from older leaves and shoot. Nonetheless cultivars varied for remobilization but differences in P remobilization could not explain the differences in P utilization efficiency among cultivars. Hence further experimentation to study root morphology, P uptake, and organic acid exudation by these cultivars in relation to P deficiency is recommended.

Comparison of Low-Molecular-Weight Organic Acids and Ethylenediaminetetraacetic Acid to Enhance Phytoextraction of Heavy Metals by Maize

We compared acetic, ascorbic, and oxalic acids with ethylenediaminetetraacetic acid (EDTA) to enhance phytoextraction of nickel (Ni), manganese (Mn), zinc (Zn), copper (Cu), cadmium (Cd), and lead (Pb) by maize. Except ascorbic acid, acids significantly (P < 0.05) decreased shoot dry weight with maximum (5.60 g pot−1) recorded with ascorbic acid and minimum with oxalic acid (4.06 g pot−1). Maximum ammonium bicarbonate–diethylenetriaminepenta acetic acid (AB-DTPA)–extractable nickel (19.94 mg kg−1) was recorded with EDTA and it was minimum (10.57 mg kg−1) with oxalic acid. The EDTA significantly (P < 0.05) increased AB-DTPA-extractable lead while other acids decreased it. Except acetic acid, other acids significantly (P < 0.05) increased Ni and Zn concentration in shoots with maximum Ni (9.22 mg kg−1) and Zn (37.40 mg kg−1) with EDTA.