Journal of Environmental Biology

Population dynamics of free living, nitrogen fixing bacteria

Azospirillum in Manakkudi mangrove ecosystem, India

Author Details

S. Ravikumar

(Corresponding author)

School of Marine Sciences, Department of Oceanography and Coastal Area Studies, Alagappa

University, Thondi Campus, Thondi - 623 409, India

e-mail: ravibiotech201321@gmail.com

M. Gnanadesigan

School of Marine Sciences, Department of Oceanography and Coastal Area Studies, Alagappa

University, Thondi Campus, Thondi - 623 409, India

S. Thadedus Maria Ignatiammal

Department of Botany, Holy Cross College, Nagercoil ? 629 004, India

S. Sumaya

Thassim Beevi Abdul Kadar College for Women, Kilakarai- 623 517, India

Publication Data

Paper received:

07 October 2010

Revised received:

10 March 2011

Re-revised received:

18 April 2011

Accepted:

23 April 2011

Abstract

Seasonal variations of population dynamics of free living nitrogen fixing bacteria, Azospirillum in relation to chemical parameters in Manakkudi mangrove eco system was assessed in root and rhizosphere soil samples of mangroves and mangrove associated plants. In rhizosphere soil and root samples, the counts of Azospirillum were recorded maximum in Acrostichum aureum as 8.63?0.92 x10⁴ and 115.48?17.36 x 10⁴ CFU g^-1, respectively. The counts of Azospirillum in non-rhizosphere soil varied from 0.01?0.001x 10⁴ to 5.77?0.92x 10⁴ CFU g^-1 and found maximum in February and minimum in March and September. Azospirillum counts in water samples were found maximum (2.24 x 10⁴ CFU l^-1) in February. During seasonal variations maximum counts of Azospirillum were recorded during southwest monsoon season in Avicennia officinalis (1.40 x 10⁴? CFU g^-1 ) followed by Rhizophora mucronata (1.07 x 10⁴? CFU g^-1). The average maximum population density of Azospirillum counts was found during non monsoon season (9.73 x 10⁴? CFU g^-1 ) and the average maximum population density of Azospirillum counts was found with the mangrove associated root samples (13.73 x 10⁴ CFU g^-1 ). Of the selected isolates Azospirillum lipoferum (60%) was found to be predominant followed by Azospirillum brasilense (25%), Azospirillum irakense (5%), Azospirillum halopraeferens (5%) and Azospirillum amazonense (5%). Of the isolated species, A. halopraeferens exhibited better growth at 35 g l^-1 NaCl. The level of Fe, Cu, Zn and Mn were varied from 0.91 to 15.93 ppm.? The level of Mn (12.13 ppm) was found maximum during non-monsoon of rhizosphere soil sample. Highest rainfall (192.80 mm) and atmospheric temperature (25.10 ^oC) were recorded during south west monsoon and non monsoon seasons. The increased population density was greatly influenced by the pH (r=+0.686). The present finding provides enough information on the nitrogen flow through biological process in Manakkudi mangrove ecosystem which can be useful for the effective implementation of mangrove management plan.? ??????

Key words

Azospirillum, Ecosystem, Mangrove forest, Nutrient cycle ???

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