EFFECTS OF UV-B RADIATION ON TERRESTRIAL PLANTS AND ECOSYSTEMS - INTERACTION WITH CO2 ENRICHMENT

UV-B radiation is just one of the environmental factors, that affect p lant growth. It is now widely accepted that realistic assessment of pl ant responses to enhanced UV-B should be performed at sufficiently hig h Photosynthetically Active Radiation (PAR), preferably under field co nditions. This will often imply, that responses of plants to enhanced UV-B in the field will be assessed under simultaneous water shortage, nutrient deficiency and variation of temperature. Since atmospheric CO 2 enrichment, global warming and increasing UV-B radiation represent c omponents of global climatic change, interactions of UV-B with CO2 enr ichment and temperature are particularly relevant. Only few relevant U V-B x CO2 interaction studies have been published. Most of these studi es refer to greenhouse experiments. We report a significant CO2 x UV-B interaction for the total plant dry weight and root dry weight of the C-3-grass Elymus athericus. At elevated CO2 (720 mu mol mol(-1)), pla nt growth was much less reduced by enhanced UV-B than at ambient atmos pheric CO2 although there were significant (positive) CO2 effects and (negative) UV-B effects on plant growth. Most other CO2 x UV-B studies do not report significant interactions on total plant biomass. This l ack of CO2 x UV-B interactions may result from the fact that primary m etabolic targets for CO2 and UVB are different. UV-B and CO2 may diffe rentially affect plant morphogenetic parameters: biomass allocation, b ranching, flowering, leaf thickness, emergence and senescence. Such mo re subtle interactions between CO2 and UV-B need careful and long term experimentation to be detected. In the case of no significant CO2 x U V-B interactions, combined CO2 and UV-B effects will be additive. Plan ts differ in their response to CO2 and UV-B, they respond in general p ositively to elevated CO2 and negatively to enhanced UV-B. Moreover, p lant species differ in their responsiveness to CO2 and UV-B. Therefore , even in case of additive CO2 and UV-B effects, plant competitive rel ationships may change markedly under current climatic change with simu ltaneous enhanced atmospheric CO2 and solar UV-B radiation.