Quantifying foliar uptake of gaseous nitrogen dioxide using enriched foliar delta N-15 values

The magnitude and impact of gaseous nitrogen dioxide (NO2) directly entering the leaves were investigated using foliar nitrogen isotopic composition (delta N-15) values in tomato (Lycopersicon esculentum) and tobacco (Nicotiana tabacum). Using a hydroponics-fumigation system, (NO2)-N-15 (20 and 40 ppb) was supplied to shoot systems and NO3-(50 and 500 mu M) was supplied to root systems. Morphological, stable isotope and nitrate reductase activity (NRA) analyses were used to quantify foliar NO2 uptake and to examine whether realistic concentrations of NO2 influenced plant metabolism. Nicotiana tabacum and L. esculentum incorporated 15 and 11%, respectively, of (NO2)-N-15-N into total biomass via foliar uptake under low NO3- availability. There were no strong effects on biomass accumulation or allocation, leaf delta C-13 values, or leaf or root NRA in response to NO2 exposure. Foliar NO2 uptake may contribute a significant proportion of N to plant metabolism under N-limited conditions, does not strongly influence growth at 40 ppb, and may be traced using foliar delta N-15 values.