Arsenic Bio-regulation Management and Altered Plant Physiology under Different Irrigation Regime

Majumdar, Arnab (2021) Arsenic Bio-regulation Management and Altered Plant Physiology under Different Irrigation Regime. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Arnab Majumdar (18RS024)) 18RS024.pdf - Submitted Version Restricted to Repository staff only Download (9MB)

Abstract

Arsenic (74.924As³³) contamination in groundwater aquifer and subsequently to the soil-plant systems is a natural hazard causing millions of peoples affected. A major problem lies within the conventional agronomic practices that use flooded fields for the rice cultivation globally using As laden water. To address both of these problems, this thesis work was divided into four parts with distinct aims to reduce the As contamination from the soil followed by minimized translocation to the rice plants, defining also the role of soil microbial community in As modulation. In the beginning, the groundwater As removal was aimed by rhizofiltration approach using water hyacinth to phytoaccumulate the water As content within a short time span. The treated water can be used in bulk volume for crop cultivation without any As input to the soil. Considering the threat of phytoremediated plants getting degraded and As being reverted back to the environment, the hyacinths were bioconverted to an organic fertilizer, vermicompost, using earth worms, which was further tested for its ability to restrict the mobility and bioavailability of As. Selected vegetative pot culture shown the efficiency of vermicompost for growth enhancement without allowing any As translocation to the plant system. In the next phase, soil As content measurement and the effect of differential soil physico-chemical parameters on soil As dynamics and relation with available silicon (Si) were analyzed. Structural analogy of Si with As influences the geochemical competition which was thoroughly studied using several quantitative instrumentation and qualitative analysis of plant ultra-structure physiology, enzyme activities and statistical justifications. These results shown the greater uptake of Si suppressed As translocation in plants. All of these experiments were carried out using two different irrigation regimes: dry-wet or intermittent and conventional flooded. Continuing this study, the proposed dry-wet irrigation was further tested for soil As flux measurement using two newly developed season-specific equations. It was clearly observed that the wintery (boro) rice cultivation hindered As accumulation in plants compared to the monsoonal (aman) cultivation due to lesser redox change in winter. This redox alteration and water stagnancy also modulated soil microbial community where distinct results from next generation metagenomics showed that the dry-wet field was more microbial enriched having a positive correlation with lesser As availability. Such irrigation allowed indigenous microbes to become more As resistant as confirmed by consecutive screening. Selected high As resistant bacteria was used for plant growth promotion and restricted As translocation in both hydroponics and pot culture, and to be used further as a bio-enhancer.

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