<atl>Differences in growth rate, nitrogen fixation and numbers of cyanobionts and heterocysts among three Azolla pinnata var. pinnata strains

The differences in nitrogen fixation, growth rate and numbers of cyanobionts and heterocysts among three Azolla pinnata var. pinnata strains were examined. The relative growth rate (RGR) and nitrogen fixation of PP7002 and PP7003 were significantly low compared with those of PP7005. The application of ammonium ions at 0.2 mM or more increased the growth rate of PP7002 and PP7003, but not PP7005. The numbers of cyanobionts and heterocysts in the mature region of PP7002 and PP7003 were statistically lower than those of PP7005. The low nitrogen-fixing activity of PP7002 and PP7003 as compared with PP7005 might be related to the restricted number of heterocysts. In PP7002 and PP7003, nitrogen fixation might be insufficient for full growth. [Copyright &y& Elsevier]