Short‐term exposure to atmospheric ammonia does not affect low‐temperature hardening of winter wheat

The effect of atmospheric NH3 on low-temperature hardening of winter wheat (Triticum aestivum L. cv. Urban) was investigated. Growth and photosynthesis were stimulated by ammonia exposure. After a 14 d exposure at moderate temperatures (day/night 18.5/16 degrees C) total nitrogen content was enhanced by 45% compared with the controls. During that period, water-soluble sugar content was not affected by NH3. After lowering the temperature to 4/3 degrees C, sugar content of the control plants doubled within 2 d, whereas in the plants exposed to NH3 it increased to a much lesser extent. Total nitrogen content further increased, leading to an 85% higher level in the NH3-exposed plants. Frost hardiness was not affected by atmospheric ammonia. It is concluded that winter wheat is tolerant to high ammonia concentrations, even under unfavourable growth conditions.