Bioremediation of Arsenic-Contaminated Water: Recent Advances and Future Prospects

Arsenic contamination of groundwater and surface water is widespread throughout the world. Considering its carcinogenicity and toxicity to human and animal health, remediation of arsenic-contaminated water has become a high priority. There are several physicochemical-based conventional technologies available for removing arsenic from water. However, these technologies possess a number of limitations such as high cost and generation of toxic by-products, etc. Therefore, research on new sustainable and cost-effective arsenic removal technologies for water has recently become an area of intense research activity. Bioremediation technology offers great potential for possible future application in decontamination of pollutants from the natural environment. It is not only environmentally friendly but cost-effective as well. This review focuses on the state-of-art knowledge of currently available arsenic remediation methods, their prospects, and recent advances with particular emphasis on bioremediation strategies.     

Effects of selected natural factors on soil ph and element dynamics studied in columns of pyritic sediments

Two sets of column (70 cm)-leaching experiments were carried out by using pyritic marine sediments of Kojima lake (Okayama, Japan) to evaluate the influence of soil microorganisms (SMO), duration of oxidation, intensity of rainfall, and groundwater level on the changes in soil pH and dynamics of associated elements. The soil contained 6.5 g kg^-1 pyrite, 43 g kg^-1 organic carbon, and had a pH value of 8.0 determined by the sticky point method. The pH of the non-sterile soils (with SMO=set I) showed an acidic range (pH <6.5) after 2 weeks of incubation. A pronounced decrease of the pH (3–4) was detected during the 32-week period of incubation, while a more alkaline range of pH (>8.5) was recorded at the lower depths (40–50 cm) with the passage of time in most of the soils initially sterilized (without SMO=set II). When the water (25±2% air v.) content was about 200%, the pH of the non-sterile soils was less than 6 after 16 weeks of incubation, while for the same water content at 32 weeks after incubation, the pH of the soils was about 1 unit lower than that of the 16 weeks after incubation. However, the pH in sterilized soils was less than 6 after 32 weeks of incubation for a water content of about 150% (40±2% air v.), whereas, at such (40±2% air v.) levels of water or oxygenation, the pH of the soils decreased to about 3 in all the treatments with SMO. Application of rainfall and changes in the groundwater significantly (p≤0.01) enhanced the development of acidity in the top soils (0–15 cm) through leaching losses of Ca²⁺ and Mg²⁺, and led to a substantial increase of the amounts of water-extractable Fe³⁺ and A1³⁺, indicating that the soils may have become permanently acidic through leaching.     

Effect of Aluminum and Silicon in Solution on the Growth of Rice (Oryza sativa L.) uspension Cells

Cells of two indica rice (Oryza sativa L.) varieties, one aluminum-tolerant (IAC3), and the other aluminum-sensitive (IR45), were grown in suspension culture in a medium with or without Al (0-800 µM), Si (0-2,000 µM), or Al and Si in combination as well as in R2 medium as control. The influence of Al or Si on cell growth was evaluated based on the growth of the cells in the treatment medium as well as in the R2 medium and compared with the effect on rice seedlings. Similar responses were observed for the cells and the seedlings; Al treatment resulted in a significant reduction of cell growth in both varieties, and the growth was reduced with the increase of the Al uptake by the cells. IAC3 was more tolerant to Al and it absorbed more Al than IR45. On the contrary, Si alone had almost no effect or exerted a negligible effect on the cell growth in both varieties and Si was hardly absorbed by the cells. There was a slight alleviative effect of Si on Al toxicity in the suspension cells of IR45, whereas, a considerable ameliorative effect in the seedlings. The content of total Al and of AI insoluble in citric acid in the cells were higher in the sole Al (800 µM) treatment than in the Al-Si combination treatment. This tendency was also observed in aluminon staining. The differences in the alleviative effects of Si and the uptake of Al and Si between the suspension cells and seedlings may have resulted from the presence of roots and morphological differences in the apoplastic tissues.     

Adequate range of boron nutrition is more restricted for root nodule development than for plant growth in young soybean plant

A pot experiment was conducted under growth chamber conditions to determine the lower and upper critical levels of boron (B) for plant growth, nodule development, and nodule acetylene reduction activity (ARA) in young soybean plants. Plants of a soybean cultivar, Tachinagaha, were grown in pots containing river sand to which a nutrient solution with different B levels was added and were inoculated with Bradyrhizobium japonicum A1017. At 8, 12, and 16 d after sowing (DAS), among the plants supplied with the solution at 0, 1.0, and 2.0 mg B L^-1 , plants with 1.0 mg B L^-1 showed the highest values for dry shoot and fresh root weight, root length, total number of developing nodules and meristematic nodules (DMN), and ARA. At 20 DAS plants grown with 11 B levels (0-2.0 mg L^-1) were compared. The B critical deficiency levels for soybean dry shoot weight, fresh root weight, root length, DMN, number of complete nodules, and ARA were approximately 46, 35, 34, 57, 60, and 50 mg B kg^-1 dry matter, and the critical toxicity levels were approximately 114, 137, 134, 97, 104, and 89 mg B kg^-1 dry matter, respectively. The optimum B levels for the growth characters were approximately 34 to 137 mg B kg^-1 dry matter. The optimum range of B levels for nodule formation and function was more restricted than that for the growth characters. Based on the results of treatments with various B concentrations, 0.4 mg B L^-1 was found to be the concentration most beneficial for all the growth characters including nodule formation at the early stage (20 DAS) of development of soybean plants.     

Variation in photosensitivity of flowering in the world soybean mini-core collections (GmWMC)

ABSTRACT

Photosensitivity of flowering is the main yield limiting factor for soybean production in tropical areas. Our objective was to evaluate the variation of photosensitivity in the world soybean mini-core collections (GmWMC) under controlled environment. Ten and 13 h were selected as short- and long- photoperiods. The days from emergence to first flower open (DEF) were 20–49 days under 13 h, whereas 20–31 days under 10 h photoperiods. The variation in DEF under short photoperiod might be caused by juvenile growth phase or post-inductive phase, because 10 h was the photoperiod which induction phase of most genotypes were minimized. Index of photosensitivity of flowering (IPF) varied from 0.00 to 0.47 and correlated positively with DEF under short photoperiod. However, some genotypes were found having higher IPF but shorter DEF, or lower IPF but longer DEF. Results provided the valuable information for soybean production in tropical areas.     

Effect of rhizosphere microbiome on different crop growing fields in various rice cultivars and its molecular approaches for sustainable agro-ecosystem

Journal of Crop Science and Biotechnology - The present investigation was carried out to investigate the effects of rhizosphere bacteria on growth and rice yields. Also, isolation and...     

Silicon biostimulant enhances the growth characteristics and fortifies the bioactive compounds in common and Tartary buckwheat plant

Journal of Crop Science and Biotechnology - Silicon is a potential biostimulant that has been used to enhance the yield and quality of plant products. Therefore, we aimed to evaluate the effect of...     

Pollution attenuation by roadside greenbelt in and around urban areas

Greenbelts are effective tools for mitigation of traffic induced air and noise pollution. In this study, the potential role of greenbelts along the roadside for the reduction of air pollution and noise levels has been assessed by using seasonally monitored data in a megacity of Bangladesh. Correlation analysis was performed between the vegetation status, measured by canopy density and shelterbelt porosity, and the total suspended particles (TSP) removal percentage. Further, the reduction of noise level was also analyzed. The results showed that the greenbelts greatly contributed to reduce TSP pollution and it was as much as 65%. Noise level reduction was also achieved up to 17 dB when compared to the open area. Moreover, TSP removal percentage was correlated to the crown density. Area having higher crown density demonstrated less air pollution and lower level of noise compared to the area having lower crown density. Greenbelt showed better performance in summer time than winter.     

Allometric relationship for estimating above-ground biomass of Aegialitis rotundifolia Roxb. of Sundarbans mangrove forest, in Bangladesh

Tree biomass plays a key role in sustainable management by providing different aspects of ecosystem. Estimation of above ground biomass by non-destructive means requires the development of allometric equations. Most researchers used DBH (diameter at breast height) and TH (total height) to develop allometric equation for a tree. Very few species-specific allometric equations are currently available for shrubs to estimate of biomass from measured plant attributes. Therefore, we used some of readily measurable variables to develop allometric equations such as girth at collar-height (GCH) and height of girth measuring point (GMH) with total height (TH) for A. rotundifolia, a mangrove species of Sundarbans of Bangladesh, as it is too dwarf to take DBH and too irregular in base to take Girth at a fixed height. Linear, non-linear and logarithmic regression techniques were tried to determine the best regression model to estimate the above-ground biomass of stem, branch and leaf. A total of 186 regression equations were generated from the combination of independent variables. Best fit regression equations were determined by examining co-efficient of determination (R2), co-efficient of variation (CV), mean-square of the error (MSerror), residual mean error (Rsme), and F-value. Multiple linear regression models showed more efficient over other types of regression equation. The performance of regression equations was increased by inclusion of GMH as an independent variable along with total height and GCH.     

Patterns of tree buttressing at Lawachara National Park, Bangladesh

We describe patterns of buttress formation and development in eleven tree species at Lawachara National Park, Bangladesh. Fortyfive percent of trees of these 11 species had buttresses. Artocarpus chaplasha Roxb. showed maximum (87%) buttress formation, whereas Alstonia scholaris (L.) R. Br. did not show any buttress. Buttresses were recorded in 20% 40% of trees of six species and 40% 60% of trees in three species. Mean length and height of buttress varied among the species and ranged from 0.37 1.37 m and 0.71 2.13 m, respectively. Buttress height, mean buttress length, total buttress length, and total length pluslength of secondaries increased with DBH (diameter at breast height) and tree height. Buttress number did not increase with DBH or tree height.Under-storey and mid-canopy trees produced less developed buttresses than did emergent trees (p<0.01). Wood density showed moderate effects on buttress characters (p<0.05), while the slope of the land did not. Canopy category was a primary regulating factor for tree buttressing, suggesting that buttresses are mechanical adaptations of trees to counter physical stresses.