Photosynthesis and growth response of Calamagrostis arundinacea and C. villosa to enhanced UV-B radiation

Calamagrostis arundinacea L. (Roth.) and C. villosa (Chaix.) J.F. Gmel are two grass species substituting forest communities on deforested areas in Central Europe. They were exposed to enhanced ultraviolet-B (UV-B, λ = 290–320 nm) radiation during 22 weeks. A system of modulated lamps operating under field conditions was used to simulate a 25 % increase of incident UV-B radiation. CO₂ assimilation seemed to be limited by a decrease of stomatal conductance (g _s) in C. arundinacea, whereas carboxylation activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) was not affected. On the contrary, g _s and RuBPCO activity decreased in C. villosa. These physiological adjustments resulted in growth changes; above-ground biomass decreased in C. villosa (prevailing negative effect) and significantly increased in C. arundinacea (prevailing positive effect) in response to enhanced UV-B radiation.