Responses of morphological, physiological, and biochemical parameters in Euglena gracilis to 7-days exposure to two commonly used fertilizers DAP and urea

Diammonium phosphate (DAP) and urea are commonly used fertilizers throughout the world. The effects of these fertilizers on the freshwater flagellate Euglena gracilis was studied after 7 days of growth using morphological, physiological and biochemical parameters as end points. NOEC and EC50 values for various parameters like cell density, motility, velocity, cell shape, gravitaxis, chlorophyll a, b and total carotenoids were calculated. NOEC and EC50 values of DAP varied from 0.5 to 2.5 g L-1 and 3.14 to 5.96 g L-1, respectively, for different parameters. NOEC and EC50 values for urea ranged from 5 to 25 g L-1 and 28 to 44.05 g L-1, respectively, for various parameters. Photosynthetic pigments were found to be more sensitive to both fertilizers as compared to other measured end points. The NOEC and EC50 values obtained for DAP were much lower than those for urea; i.e., DAP showed a stronger inhibitory effect as compared to urea. Application of DAP resulted in an increased concentration of ammonia in Euglena cultures but urea did not. The stronger inhibitory effect of DAP is attributed to release of free ammonia in the culture due to DAP decompostion. No release of ammonia by urea occurred due to the absence of the enzyme urease in E. gracilis.