Nitrogen derived from atmospheric nitrogen dioxide (NO
2) in plant tissue was determined by the
15N dilution method. Seedlings of sunflower, tomato and rice plants which were grown in nutrient solution containing
15N-labelled nitrogenous compounds were exposed to low concentrations (0.1 and 0.2 ppm, v/v) of NO2 for three weeks. Dilution rate of
15N abundance in plant tissue by NO
2 was calculated by the following equation.
Rate= (1-
15N abundance in plant tissue/
15N abundaace in nutnient sohltion)
Amount of NO
2-nitrogen was determined by multiplying the rate by total nitrogen in plant.
The dilution rate of
15N abundance in plant tissue was proportional to the concentrations of NO
2, indicating the rate can be used as an indicator of NO
2 level in the atmosphere. Plant species with a higher rate of
15N dilution would be suitable for the detection of difference in NO
2 levels among sites. Critical concentration of NO
2 detectable by the method employed in the present study was 42-44 ppb.
The results indicated that the
15N dilution method would be applicable for the biomonitoring of NOx pollution in the atmosphere.
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