Aspects of nitrogen assimilation by cultures of green algae
1956
Bongers, L.H.J.
The N/C relation in green algae was about 0.2, but with N starvation this ratio may decline to 0.04. Such treatment also decreased the chlorophyll content of the cells as well as the rates of photosynthesis and growth.Supply of substrate N to N-starved algae resulted in formation of cells of 'normal' character. At pH values of 7 to 8, both NO 2- and N0 3- were assimilated at approximately the same rate.Algae of normal N/C relation did not assimilate substrate N (NO 2 - or NO 3 -) if illuminated without a carbon source. Instead, NO 3 - and NO 2- became reduced and NH 3 was excreted into the surrounding medium.In weak light, the rate of NH 3 excretion (i.e. reduction of NO 3 - in the absence of CO 2 ) was equivalent to the rate of CO 2 reduction (in the absence of N0 3- ); if both substrates ( NO 3- + CO 2 ) were present together both rates decreased, indicating competition for the same reduction.In strong light (without CO 2 ) the rate of NO 3- conversion into NH 3 was a fifth of the rate of CO 2 reduction. Nitrate and carbon dioxide did not compete for the reduction in strong light.It was concluded that nitrate reduction was not necessarily dependent upon products of photosynthesis.
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