The interactive effect of irradiance and source of nitrogen on growth and root respiration of Calamagrostis epigejos

Growth and respiratory processes of Calamagrostis epigejos (L.) Roth were studied as part of a comprehensive ecological project aimed at explaining the acclimation potential of some perennial grasses upon changes in climatic and edaphic factors after logging activity in forests. We investigated the relative growth rate (RGR), the respiration rate and the contribution of the different respiratory pathways in roots of Calamagrostis epigejos grown at two levels of irradiance and with nitrate or ammonium as N-source. The respiration rate as well as the RGR decreased significantly but the leaf area ratio (LAR) increased upon transfer to shade. The LAR increase was caused by both a greater specific leaf area (SLA) and a greater leaf weight ratio (LWR). The relative contribution of the alternative (AP) and the cytochrome pathways to total respiration rate was the same in both radiation regimes. The ammonium form of N-nutrition had a significant stimulative effect on AP activity in shaded plants. The AP capacity was significantly higher in ammonium-fed plants grown at both irradiance levels. A possible role of the AP in plants with low energy input and with ammonium ions as N-source is discussed.