Responses of Calamagrostis epigejos (L.) Roth to different levels of growth irradiance and nitrogen supply

Seedlings of Calamagrostis epigejos were grown hydroponically for six weeks to study the effects of light regime (60, 120 and 700 mu mol*m(.2)*s(-1) PAR) and nitrogen supply (0.5, 2.0 and 6.0 mM N) on growth and light dependency of CO2-gas exchange characteristics. Dry matter yields increased markedly with growth irradiance at ail N levels, whereas N-supply affected growth only at the highest light level. Light dependence curves of net photosynthesis for plants grown at 700 pmol*m(.2)*s(-1) and with high N-supply showed surprisingly high values for light saturation (1360 mu mol*m(.2)*s(-1)) and light-saturated CO2 assimilation rates (24 mu mol CO2*m(.2)*s(-1)). The light-saturated CO2 assimilation rates were strongly correlated to N-supply and leaf nitrogen content per unit leaf area. Light saturated photosynthetic rates as well as dark respiration rates declined with decreasing growth irradiance, but light saturation was at least twice as high as in typical shade plants. These findings are discussed in relation to current hypotheses concerning the invasion of Calamagrostis epigejos into pine forests.