Growth And Biomass Yield Of Maize Biology Essay
1) Postgraduate Program, University of Brawijaya, Jl. Veteran, Malang 65145, Indonesia
2) Department of Soil Science, University of Mataram, Jl. Pendidikan 37, Mataram 83125, Indonesia
3) IRC-MEDMIND, University of Brawijaya, Jl. Veteran, Malang 65145, Indonesia
* Corresponding Author E-mail Address: firstname.lastname@example.org
Received Month X, XXXX; revised Month X, XXXX; accepted Month X, XXXX
Keywords: Format, Microsoft Word Template, Style, Insert, Template
Indonesia is regarded as a major location for artisanal and small-scale gold mining (ASGM). It has been reported that there are 713 small-scale mining sites throughout Sumatra, Java, Kalimantan and Sulawesi . Mercury amalgamation is the most common method of gold recovery used by artisanal miners. This technique is favoured by miners because it is efficient, easy to use and cheap. Despite the assumed efficiency of mercury amalgamation, the ability of mercury to recover gold from ore is highly dependent upon the size and geochemistry of a gold particle (Moreno et al., 2005). A research trial conducted at an ASGM location in the Philippines reported that only 10% of the gold was recovered by amalgamation . There is also a loss of mercury into the environment through discharge of the water used for grinding, and tailings. It is estimated about two grams of mercury per gram of gold produced is lost to the environment (Krisnayanti et al., 2012). Between 100 and 150 ton per year are estimated to be released from Indonesia . Therefore, implementation of remedial procedures for metal removal toward the rehabilitation and/ or reclamation of heavy-metal polluted sites is needed . During the past decade, there has been increasing interest in the possibility of using vegetation for remediating heavy-metal contaminated sites. This technique that is commonly defined as phytoremediation, can represent a low-cost alternative to traditional techniques such as soil removal and capping . Among the different areas in the field of phytoremediation, special interest has been devoted to the phytoextraction of metals from contaminated soils. In this case, metals are removed from soils by concentrating them in the aerial parts of the plant. Harvesting and disposal of shoot biomass allows the metal to be removed in significant quantities from the soil [6, 7].
The success of phytoextraction depends on the availability of the metal in soil for plant uptake . For example, Hg that is mostly found in soils as an uncharged complex in soil solution has limited solubility in soils , and thus low availability for plant uptake. Therefore, uptake of Hg by plant will depend on the ability of plant to control the processes that enhance the concentration of Hg in the soil solution . The coordination chemistry of Hg suggests that this element will be present mostly as a complex in soil solution. The partitioning of Hg from the solid phase into soil solution will occur as a consequence of coordinative reactions where Hg ions are exchanged with water molecules for some preferred ligands . In mildly reduced environments and in the presence of other metal sulfides or sulfhydril groups, Hg will precipitate as insoluble cinnabar (HgS) . Additionally, the strong affinity of Hg to organic matter influences Hg solid phase speciation and it is regarded as one of the major driving forces for Hg adsorption by soil particles .
Previous study has reported that from six wild plant species evaluated for their phytoremediation potential there three species, i.e. Lindernia crustacea (L.) F., Paspalum conjugatum L., and Cyperus kyllingia Endl. can be used for phytoextraction of Hg since they were efficient to take up and translocate mercury from roots to shoots .Therefore, the aims of this study were to elucidate the potential of the three wild plant species for phytoremediation of mercury-contaminated soils in conjunction with the thiosulphate to phytoextract mercury and its effect on maize growth.
2. Materials and Methods
This study was carried out in a shade house belonging to farmers having agricultural lands contaminated with small-scale gold mine tailing containing mercury. The site is located at Sekotong District of West Lombok, Indonesia (1150.46’-1160.20’E and 80.25’-80.55’S). Pot experiments were conducted from July to December 2012. Samples of soil contaminated with gold mine tailing were collected at 0-30 cm depth. The samples were air dried at room temperature for two weeks, crushed and ground to pass through 2-mm sieve for analyses of texture (Bouycous hydrometer method), pH (1:2.5 soil-water suspension), and N (Kjeldahl method), P (Olsen method), C organic (Walkley and Black method) and Hg (Cold Atomic Absorption Mercury Vapor analyzer) contents. Results of soil sample analyses showed the soil characteristics as follows: sandy loam texture pH 7.1, 1.3% C organic, 0.2% N, 20.5 mg P kg-1, and 88.9 mg Hg kg-1. The value mercury content in the soils was much higher than the tolerable mercury concentration of 0.002 mg kg-1 regulated by the Indonesian Ministry of Environment. Lindernia crustacea L., Paspalum conjugatum L., and Cyperus kyllingia Endl. used for this study were two-week old acclimatized seedlings previously collected from areas nearby the small-scale gold mine location.
2.1. Phytoextraction of mercury
Each of the three seedlings was planted in a plastic pot containing 15 kg of mercury-contaminated soil for 9 weeks. Treatments tested were (1) plant species (three species), and (2) rates of ammonium thiosulphate ([NH4]2S2O3) application, i.e. 0 and 8 g ammonium thiosulphate/ kg of soil . To ensure plant growth, all pots received basal fertilizers of N, P and K with rates equivalent to 100, 50 and 20 kg ha-1, respectively. Six treatments (combinations of three plant species and two rates of ammonium thiosulphate application) were arranged in a randomized block design with three replicates. The plants were grown for 9 weeks. During the experiment, water was regularly supplied to ensure that water did not limit plant growth. At harvest (9 weeks), shoots and roots were separated, washed, weighed and oven dried at 600C for 48 hours for mercury analysis using the method describe above. The concentration of mercury was determined using a F732-S Cold Atomic Absorption Mercury Vapor analyzer (Shanghai Huaguang Instrument Company) that works on the reduction of mercury by stannum chloride (SnCl2). Data obtained were subjected to analysis variance followed by 5% last significance different test.
2.2. Growth and biomass yield of maize
After harvesting the phytoremediation plants, the remaining soils in the pots were used for growing maize. Six treatments similar to those of experiment 1 and one control treatment (mercury contaminated soil with no phytoremediation treatment) were arranged in a randomized block design with three replicates. Each pot received basal fertilizers equivalent to 100kg N ha-1 (supplied as Urea), 50kg P ha-1 (supplied as SP36), 50kg K ha-1 (supplied as KCl), and 10 kg compost ha-1 . During the experiment, soil moisture was maintained at 80% of field capacity by adding water periodically. Maize was harvested at maximum vegetative period (70 days). Maize shoots and roots were separated, washed, weighed and oven dried at 600C for 48 hours for mercury analysis. Mercury concentration in the maize shoot and roots was analyzed using the method similar to that of experiment 1. The data obtained were subjected to analysis variance followed by 5% last significance different test
3. Results and Discussion
3.1. Plant biomass
The test results of three plant species tolerance capabilities suggested that all plants showed high tolerance to soil contaminated with gold mine tailings containing mercury. This was demonstrated by the absence of inhibition of plant growth and no visible physical damage that showed toxicity symptoms at all plants. The shoot and root dry weights produced by P.conjugatum were not significantly different from those of C.kyllingia and L.crustacea (Figures 1 and 2).
Figure 1. Shoot dry weight of three plant species grown for 9 weeks
Figure 2. Root dry weight of three plant species grown for 9 weeks
Based on the statistical analysis it was known that in general the addition of ammonium thiosulphate exerted a significant effect on the dry weight of shoots on all plants tested. However, the addition of ammonium thiosulphate did not significantly (p<0.05) increase root dry weights. A type of plant to be classified as heavy metal accumulator group must meet the criteria in addition to having the ability to withstand high concentrations of metals in the soil, the level of uptake and translocation of metals in tissues with a high rate should ideally also have a high potential for biomass production . Figures 1 and 2 show that at 9 weeks, P.conjugatum has the highest potential to produce biomass followed by L.crustacea and C.kyllingia. In terms of biomass production, P. conjugatum seemed to be the best plant species for phytoremediation of mercury-contaminated soils.
3.2. Mercury accumulation in plants
The highest concentration of mercury was found in P.conjugatum followed by L.crustacea and C.kyllingia, both with and without addition of ammonium thiosulphate. Addition of ammonium thiosulphate in media did not significantly increase Hg content in the shoots of all plant tested, but significantly improved the content of Hg in the root. Plants develop some effective mechanisms to tolerate high levels of metals in the soil . Accumulator plants did not prevent the metal into the roots but develop specific mechanisms to detoxify heavy metals in soils with high levels in the cell that allows the bioaccumulation of metals in high concentrations . High accumulation in plant species reflects the high concentration of metals in the rhizosphere. Plants can naturally accumulate metals exceeding a threshold value of 1% (Zn, Mn), 0.1% (Ni, Co, Cr, Pb and Al), 0.01% (Cd and Se), 0.001% (Hg) or 0.0001% (Au) of the weight of dry biomass without showing any symptoms of poisoning .
The calculation of the content or the accumulation of Hg and comparison of accumulation of Hg in each plant species presented in Figure 3 shows a difference in ability to accumulate Hg. Hg accumulation was high in Paspalum conjugatum, followed by L.crustacea and C.kyllingia. Highest root Hg accumulation was observed in L.crustacea followed by P.conjugatum, and C.kyllingia. High biomass production provides a meaningful influence on the accumulation of Hg (Hg yield per plant dry weight). Addition of ammonium thiosulphate at planting media significantly increased the accumulation of Hg in the plant shoots and roots. With no addition of thiosulphate, accumulation of mercury by L.crustacea, P.conjugatum, and C.kyllingia shoots at 9 weeks ranged from 9.0 mg kg-1 (L.crustacea) to 32.5 mg kg-1 (P.conjugatum). These values were significantly (<p0.05) lower than that of ammonium thiosulphate treatment that ranged from 21.0 mg kg-1 (C.kyllingia) to 39.1 mg ha-1 (P.conjugatum) (Figure 3). A study conducted previously on soil contaminated with gold cyanidation tailing showed that the three plant species accumulated 9,06, 10.36 and 15,65 mg Hg kg-1, respectively . This figure exceeded the threshold value of mercury concentration of 0.001% or 10 mg kg-1 of total dry weight . Previous workers suggested that there is a relationship between the levels of heavy metal pollution in the soil by absorption by plants . Accumulation occurs because there is a tendency of heavy metals to form complex compounds with inorganic substances found in the body of organisms .
Addition of ammonium thiosulphate at planting media also significantly influenced the accumulation of mercury in the roots that ranged from 2.6 mg kg-1 (L. crustacea) to 3.7 mg kg-1 (P.conjugatum) (Figure. 3). With no addition of ammonium thiosulphate the accumulation of Hg in the roots ranged from 1.3 mg kg-1 (L. crustacea) to 4.0 mg kg-1 (P.conjugatum) (Figure. 3).
Figure 3. Accumulation of mercury in shoot and root of three plant species grown for 9 weeks
On average, the addition of thiosulphate increased the accumulation of Hg in plant shoots and plant roots by 82%and 47%, respectively, compared to the media without the addition of thiosulphate. This occurred because mercury has a strong affinity with thiol groups, especially complex sulphide and bisulphide [18, 19]. B.juncea has been shown to be able to concentrate Hg to 40 mg kg-1 in plant tissue after application of ammonium thiosulphate in mining waste contaminated with 2.8 mg Hg kg-1 .
Accumulated Hg ratio shoot / root on three plant species showed that all plants have Hg shoot / root ratios of more than one, both for ammonium thiosulphate treated and untreated pots (Figure 4). The ratio of Hg shoot / root of L.crustacea treated with ammonium thiosulphate was the greatest, followed by P.conjugatum, and C.kyllingia. With no addition of ammonium thiosulphate, however, the greatest ratio was observed for P. conjugatum followed by L. crustace and C. kyllingia (Figure 4)
Figure 4. Ratio of Hg accumulation in shoot and root of three plant species grown for 9 weeks
The difference in the ratio of Hg shoot / root on all plants showed differences in the effectiveness of each type of plant in transporting mercury from the root system of the shoot (as a place of accumulation) .
3.3. Growth and biomass yield of maize
At harvest (8 weeks), maize plant height varied from 16.13 cm (control) to 24.90 cm (P.conjugatum) in media without addition of ammonium thiosulphate (Figure 5). In the media with addition of ammonium thiosulphate, plant height varied from 16.13 cm (control) to 31.21 cm (P.conjugatum treatment) (Figure 5). Overall, in comparsion to the control treatment, the average improvement of plant height was 75% (without addition of thiosulphate) and 83% (with the addition of thiosulphate).
Figure 5. Height of maize grown on post-phytoremediation soil for 8 weeks
Shoot and root dry weight of maize also increased (compared to control) after phytoremediation of mercuty contaminated soil with three plant species. Consistent with the highest ability to accumulate Hg, the highest increase shoot and root dry weight of maize occurred on the P.conjugatum treatment (Figure 6). Average increase in shoot and root dry weight in soil was 40% (phytoremediation treatment without the addition of ammonium thiosulphate) and 62% (phytoremediation treatment with the addition of ammonium thiosulphate).
Figure 6. Shoot and root dry weight of maize grown on post-phytoremediation soil for 8 weeks
The lower increase in plant growth and biomass production of maize grown on post-phytoremeidation with addition of ammonium thiosulphate compared to that grown on post-phytoremediation soil with addition of ammonium thiosulphate related to the removal of mercury presented in Figure 3. The remaining mercury in media without ammonium sulphate treatment was higher that on media with ammonium thipsulphate treatment, thus inhibiting the growth of plants, in the plant, Hg are poison and cause damage to the enzyme, polynucleotide, nutrient transport system and disrupt cell membrane integrity . Roots elongation is often used as a first indication that the plants were poisoned elemental Hg . Hg toxicity symptoms in general are stunted growing seeds and roots, and inhabitation of photosynthesis process which in turn reduces crop production. Additionally Hg accumulated in root tissue can inhibit K uptake by plants . Hg absorbed by plants can lead to inactive several enzymes because Hg incorporation into sulfhydril of peroxide through the formation of reactive oxygen compounds, such as superoxide (O2), hydroxyl radical (OH-) and hydrogen peroxide (H2O2) .
P.conjugatum, C.kylingia and L.crustacea are three species of wild plants that have the potential to be used for phytoremediation of mercury-contaminated soil. Addition of ammonium thiosulphate to the mercury-contaminated soil increased mercury accumulation in plants. Growth and biomass production in maize grown on remediated soil increased 79% and 51%, especially after phytoremediation with P.conjugatum.
Authors thank to the University of Brawijaya, Indofood Research Nugraha and Directorate General for Higher Education and for financially supporting this study. Glass-house and laboratory facilities provided by the Faculty of Agriculture, University of Brawijaya, and Faculty of Science, University of Mataram are gratefully acknowledged.