Absorption of atmospheric nitrogen dioxide by rice, wheat, and barley plants: estimation by the15N-dilution method

Understanding of the impact of air pollutants on ecological systems has recently advanced in many aspects. Air pollutant absorption by plants is one of the important aspects involving the plants in ecological systems. We devised a 15N method for the quantitative estimation of the amount of nitrogen dioxide (NO2) absorbed by plants over a long period (2, 5). First, in a water culture experiment, 15N was administered as medium nitrogen from which the atmospheric NO2-nitrogen absorbed in the plants was discriminated (2). This 15N method was then modified in a soil culture experiment where 15N was applied as a fertilizer nitrogen and the amount of NO2-nitrogen in the plants was estimated by introducing the assumption that the ratios of fertilizer nitrogen to soil nitrogen absorbed in control and NO2-fumigated plants are the same in each of various plant parts investigated (5). In a previous report (5), it was found that the equation proposed by Fried and Middelboe (1) for the measurement of the amount of dinitrogen fixed by legume crops was also useful in measuring the NO2-nitrogen absorbed by plants. The equation by Fried and Middelboe was generalized by Rennie et al. as the 15N-dilution method (3). The 15N-dilution method is applicable for estimating the nitrogen originating from atmospheric NO2 (4), where the following equation is used.