Impact of atmospheric NH3 deposition on plant growth and functioning — a case study with Brassica oleracea L.

Brassica oleracea L. (curly kale) was exposed to 0, 2, 4, 6 and 8 µl l−1 NH3 during one week and the impact on growth and N compounds was determined. Exposure to NH3 increased shoot biomass production at 2 and 4 µl l−1, but resulted in an inhibition of shoot and root growth at 6 and 8 µl l−1. Shoot to root ratio was not affected up to 4 µl l−1, but decreased at higher levels. Shoot total N content was increased at all levels, mainly due to the increase in free amino acids. Even at atmospheric NH3 levels, at which the foliarly absorbed NH3 would cover a limited proportion of N requirement there was already an enhancement of the nitrogen content of the shoots and roots. Apparently there was no direct regulatory control of and/or interaction between atmospheric and pedospheric nitrogen utilization in B. oleracea. It needs to be evaluated to what extent foliarly absorbed NH3 is used as nitrogen source for growth.