ABSTRACT
Five species of Azospirillum isolated from Manakkudi mangrove ecosystem were subjected for their efficiency to find out their growth parameters potential for the successful establishment of mangrove seedlings. Of the isolated five Azospirillum species, Azospirillum lipoferum (60%) was found to be the dominant one. But the level of maximum indole acetic acid (IAA) production (19.8mg.ml-1) and nitrogen fixation (5.9 C2H2hr-1) was identified with A. brasilense. Further, A. brasilense showed significant (p<0.05) level of increased growth parameters [maximum root length (29.55%), average root length (7.39%), total Chl (55.36%), carrotenoids (28.57%), Chl b (37.50%), carbohydrates (90.91%) and total amino acids (78.95%)] in Avicennia officinals when compared with control group. Further, A. brasilense also showed significant (p<0.05) level of increased growth parameters [average number of primary roots (40%), average biomass (44.44%), average shoot biomass (55.56%), total Chl (20%), Chl b (77.78%) and carotenoid (1.54%)] in C. decandra seedlings when compared with control group. Similarly, the average number of primary roots (23.08%), average root biomass (15.52%), average shoot biomass (15.30%), carbohydrate (20%) and total amino acids (44.44%) were found significant (p<0.05) in A. irakense inoculated R. apiculata seedlings. In conclusion, Azospirillum brasilense was found better for the growth of Avicennia officinalis and Ceriops decandra seedlings, but Azospirillum irakense was found better for Rhizophora apiculata seedlings.
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.