Population dynamics of cyanobacteria in alluvial rice grown soils of lower Brahmaputra floodplain

Abstract The present investigation was carried out to study the cyanobacterial diversity and population dynamics during different months in relation to soil physico-chemical parameters in various rice fields in alluvial flood plain of the Brahmaputra River. Altogether 71 species of cyanobacteria under 20 genera and 9 families were recorded. Among the species heterocystous filamentous were dominant (80%) over the other forms and Nostocaceae (54%) was predominant in all the three sites followed by Chroococcaceae (14%) and Rivulariaceae (13%) respectively. In case of population number it ranged in between 0.14±x10 4 /g to 9.35±9.68x10 4 /g of soil. It was recorded highest during July-August (monsoon season) followed by September-October (post monsoon), March-June (pre monsoon) and November-February (winter season) respectively. Principle component analysis (PCA) justified the seasonal pattern and identified close relation to soil parameters like temperature, moisture, pH, phosphorus and sodium. Pearson's correlation analysis also revealed significant negative correlation of cyanobacterial number with soil nitrogen, organic carbon and conductivity in the floodplain soils