THE IMPACT OF ATMOSPHERIC AMMONIA AND TEMPERATURE ON GROWTH AND NITROGEN-METABOLISM OF WINTER-WHEAT

The effect of atmospheric ammonia in combination with low and moderate growth temperature on growth and nitrogen metabolism of winter wheat plants (Triticum aestivum L. cv. Urban) was investigated. Plants were exposed to 0, 1000 and 2000 nl l(-1) NH3 for 1 week at moderate day/ni ght temperatures (18.5/15 degrees C) and subsequently for I week at lo w temperatures (4/3 degrees C). At moderate temperatures, NH3 exposure at 1000 nl l(-1) lead to an increase in protein content, but free amm onium, amino acid and total nitrogen content were not affected. Exposu re to 2000 nl l(-1) NH3 resulted in a significantly higher amino acid, protein content and total nitrogen content, while free ammonium conte nt was not increased. Net nitrate uptake rate by the roots was decreas ed by 21% and 34% upon exposure to 1000 and 2000 nl l(-1) NH3 respecti vely. Atmospheric ammonia did not affect biomass, carbohydrates or nit rate content significantly. Lowering the temperature to 4/3 degrees C resulted in an inhibition of growth. Ammonium, amino acids, and total nitrogen accumulated in plants exposed to 1000 and 2000 nl l(-1) NH3, while protein content was not increased at this temperature. At modera te temperatures winter wheat metabolized the atmospheric ammonia and c ounteracted the extra N input via the leaves by a reduction of the nit rate uptake by the roots. At low temperatures, the complete incorporat ion of ammonia was reduced, resulting in an increased ammonium and ami no acid content. However, this disturbance of the nitrogen metabolism did not lead to any direct toxic effects. It was concluded that winter wheat is tolerant to high atmospheric ammonia concentrations, even un der unfavourable growth conditions.