106 Nitrogen Fixation Behavior of a Terrestrial Heterocystous Cyanobacterium, Nostoc Flagelliforme, as Affected by Available Nutrients in Liquid Suspension Culture

Abstract

Nostoc flagelliforme is an edible terrestrial cyanobacterium of great economic value which is often distributed in arid or semi‐arid steppes in many parts of the world. The relationship between N2‐fixing capacity and nutrient availability of N. flagelliforme under various growth conditions was investigated. Phosphorus had a profound effect on nitrogenase activity (NA) of the alga over the concentration range of 2.3 μM–0.46 mM inorganic phosphorus (Pi) in the cultures, with a maximal NA at 23 μM Pi. The optimal temperature for NA was determined by the Arrhenius equation to be approximately 25°C. However, the response of NA to different phosphorus concentrations was not affected by temperature variation. Micro‐nutrients in the media also affected NA of the alga. A 2‐fold strength of both B and Ca (relative to the standard BG110 medium) significantly enhanced NA. In addition, simultaneous enrichments with B, Ca, Fe and Mo exerted marked beneficial effects on NA, and such effects were presumably in an interactive and synergistic manner. In contrast, removal of Mo gave rise to a drastic decrease in growth rate, while the NA was only moderately decreased. NA in the Mo‐, Co‐, and Fe‐free cultures was respectively inhibited, as compared to cultures devoid of Ca, Fe, Mg, Mn, Zn and Cu, respectively. Results of the present study suggested that N. flagelliforme could be an important contributor of nitrogen to the terrestrial ecosystem because of its strong nitrogen‐fixing ability even in an infertile environment.