Abstract

AbstractIn present work, specific method was utilized for determining biologically atmospheric nitrogen fixing whichincludes three steps: digestion, distillation and titration. Nitrogen fixing was determined in seven species of localblue green algae isolates (in Mosul city), these species (Nostoc muscorum, Anabaena helicoidea, Arthrospiraplatensis, Lyngbya taylorii, Oscillatoria limnetica, Oscillatoria tenuies and Chroococcus limneticus). The bestincubation period which achieved a high amount of nitrogen fixing is fifteen day and it was reached to (20.80,19.01, 15.12, 12.48, 16.40, 16.60 and 8.01 mg/L) for understudy isolates, respectively. Also the highestpercentage of nitrogen fixing was achieved for understudy isolates which synomounosly increased withincreasing amount of nitrogen fixing, (1.48, 1.12, 1.22, 0.99, 1.28, 1.31 and 0.89%). Also, the results revealedthat the frequency of heterocysts of filamentous algae (Nostoc and Anabeana) was increased with increasingincubation period and for fifteen day. Generally, the highest rate of daily growth and weights of biomass wasachieved after fifteen day. Increasing of final pH was also observed as compared with initial pH for allunderstudy isolates and under affect all incubation period. This study revealed that the amount of nitrogen fixingfor tested isolates affected directly with exogenous nitrogen source supply into the medium, so the amount ofnitrogen fixing was increased because the utilized method determined the total amount of nitrogen in sample andalso the addition of nitrogen source into the medium stimulated the growth and elevated the biomass, proteincontent and percentage of nitrogen. Furthermore, the final pH increased significantly from initial pH under thiscondition. The results showed, a remarkable declined in heterocysts frequency when nitrogen source was addedto the medium. The effect of illumination regime on nitrogen fixation was also studied, the data revealed, that thetested isolates showed variation in their response under this condition. Nostoc, Anabeana and Arthrospirashowed maximum ability of nitrogen fixing when illuminated under (18 hour light :6 hour dark) while theremaining algae revealed maximum nitrogen fixing values when illuminated under continuous photoperiod, alsothe percentage of nitrogen fixing, the rate of daily growth rate, biomass weights and protein content showedsame manner.

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The article was added to IASJ on 2017-01-24

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