Abstract

Cyanobacteria have the ability to fix atmospheric nitrogen to plant available forms; thus, useful in producing bio-fertilizers especially for rice cultivation. In this study, cyanobacteria were isolated from soil samples collected from 23 paddy fields in Kurunegala, Matale, Anuradhapura and Polonnaruwa Districts under IL1, IM3, DL1b and DL1c agro ecological regions, respectively. Soil pH, EC, active C and exchangeable K contents varied considerably among soils from four regions. Culturable cyanobacteria were isolated using Blue Green medium (pH 7) and thirteen isolates were tentatively identified based on morphological characteristics. Oscillatoria was the most common cyanobacteria among sampling sites in IL1, IM3 and DL1c agro ecological regions. Microsystis was the most prevalent unicellular group in IL1 and DL1c agro ecological regions. In DL1b, unicellular Aphanocapsa was commonly found followed by filamentous Pseudanabaena and Oscillatoria. From this research thirteen axenic cultures were established for further studies. The diversity of cyanobacteria was high in the regions with high diversity of paddy cultivated environments.

Highlights

  • Cyanobacteria thrive in favourable growth conditions in fresh water and wetland ecosystems including lowland paddy fields, which are manmade wetland ecosystems

  • Cyanobacteria are highly abundant in paddy soils

  • Thirteen cyanobacteria genera were isolated and tentatively identified from paddy soil crust in the intermediate and dry zones of Sri Lanka based on their morphological characteristics

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Summary

Introduction

Cyanobacteria thrive in favourable growth conditions in fresh water and wetland ecosystems including lowland paddy fields, which are manmade wetland ecosystems. They live as freeliving organisms (e.g. Aphanocapsa, Gloeocapsa and Merismopedia) and in symbiotic associations Cyanobacteria are major nitrogen (N2) fixing prokaryotic organisms in the paddy field water and the uppermost soil layer (Roger, 1996). Their diversity in the rice paddies and nitrogen supplying potentials vary according to the growth stage of the rice plant

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