Acceleration of frost hardening in Vaccinium vitis-idaea by nitrogen fertilization

Vaccinium vitis-idaea L. plants were grown in open-top chambers in northern Finland under CO2 enrichment (600-700 ppm) with or without elevated (doubl e ambient) O-3. Half of the plants received ammonium ;nitrate fertilizer eq uivalent to 200 kg N ha(-1) year(-1). Frost hardiness during the period of frost hardening was determined three times after the end of the experiment, at the beginning of August, September and October. The results indicate th at frost hardening of the Vaccinium vitis-idaea is accelerated by N fertili zation. However, CO2 and O-3 enrichment had no measurable effect on frost h ardiness.