This study examined the degree to which enhanced nitrogen inputs in a Calluna-dominated ecosystem can alter plant physiological responses, affect the response of soil respiration to environmental parameters by disturbing acclimatised soil microbial populations, influence the relationship between soil carbon fluxes and soil microbial populations, and change soil mineral nitrogen availability to the plants. A pilot study investigated the response of nitrogen deposition on Calluna vulgaris plants maintained in open-top chambers. Heathland monoliths were exposed to acid mist treatments of ammonium nitrate spanning across extreme values. Growth response to increasing fertiliser additions was detectable and high nitrogen fertiliser inputs significantly stimulated shoot growth. Fertiliser inputs were reflected in soil and tissue nitrogen concentrations with an increase in total nitrogen content within actively growing tissues while shoot phenolic concentration decreased in response to nitrogen additions in agreement with the carbon-nutrient hypothesis. A field study was conducted in experimental plots set up in a dense stand of mature heather at Castlelaw Hill, near to Edinburgh. A new, simple methodology is developed and operated to accurately measure soil respiration under controlled laboratory conditions using small soil microcosm with a gas analysis unit. Annual seasonal pattern of soil carbon dioxide effluxes and environmental parameters of soil temperature, moisture, pH, organic matter, microbial biomass and plant growth were measured. Soil temperature, pH, organic matter and microbial biomass were found to be important determinants of carbon dioxide fluxes from soil. In all the soil horizons, carbon dioxide efflux in response to temperature followed the expotential first order equation with an increase with increasing temperature but soil carbon dioxide fluxes decreased with depth. Nitrogen inputs significantly increased soil respiration and the results suggest that long-term effects of atmospheric N deposition, with accelerated mineralisation at higher temperatures, could disrupt the carbon balance of nutrient-poor ecosystems, as noted for heathlands.