Paper Title
Efficiency of Native Heterocystous Cyanobacterial Isolates for Supplying Nitrogen and Improving Rice Plant Growth

The use of chemical fertilizers in rice fields has many environmental hazards because of soil waterlogging. Nitrogenous fertilizers that are very soluble, undergoes higher transformations in such conditions and are subjected to the losses and reduction in their efficiency. They thus contaminate surface and groundwater. In such situations heterocystous cyanobacteria possessing biological nitrogen fixation and plant growth promoting abilities, can be useful in supplying nitrogen to the plant. Some isolates of cyanobacteria native to the northern Iran, were effective N2 fixers as well as producing plant growth stimulants under laboratory conditions. In this study, the inoculation effects of two heterocystous cyanobacterial isolates (B0 = control, B1= Anabaena sp. GGuCy-33 and B2= Anabaena sp. GGuCy-17 ) in rice plant (Oryza sativa L. cv. Hashemi) with three levels of nitrogen fertilizer (0, 75 and 150 mg N/kg soil as urea) on growth and uptake of N, P and K were studied in greenhouse conditions. The results showed that B2 isolate increased shoot dry weight and plant height, but B1 isolate was effective in increasing dry weight of root. Nitrogen uptake of root in the presence of B2 was increased by 18.5 percent compared to the non-bacterial control. Also the B2 isolate increased shoot P uptake by 15.7% and K uptake by 33.4% in shoot compared to the control. B1 was also able to increase root nitrogen by 53.3%, root P by 29.4% and root K by 28.7% compared to the control. In the presence of B2, plant dry weight reached a highest level by using 75 mg N/kg, however a significant reduction in plant growth was recorded at 150 mg N/ kg level. Keywords - Cyanobacter, Heterocyst, Nitrogen, Phosphorus, Rice.