Stress responses of Calluna vulgaris to reduced and oxidised N applied under real world conditions

Effects and implications of reduced and oxidised N, applied under ‘real world’ conditions, since May 2002, are reported for Calluna growing on an ombrotrophic bog. Ammonia has been released from a 10 m line source generating monthly concentrations of 180e6 mg m_3, while ammonium chloride and sodium nitrate are applied in rainwater at nitrate and ammonium concentrations below 4 mM and providing up to 56 kg N ha_1 year_1 above a background deposition of 10 kg N ha_1 year_1. Ammonia concentrations, >8 mg m_3 have significantly enhanced foliar N concentrations, increased sensitivity to drought, frost and winter desiccation, spring frost damage and increased the incidence of pathogen outbreaks. The mature Calluna bushes nearest the NH3 source have turned bleached and moribund. By comparison the Calluna receiving reduced and oxidised N in rain has shown no significant visible or stress related effects with no significant increase in N status.