Increased solar UV-B radiation may reduce infection by arbuscular mycorrhizal fungi (AMF) in dune grassland plants: evidence from five years of fieldexposure

An area of coastal dune grassland, dominated by the gramineous species Cala magrostis epigeios and Carex arenaria, was exposed to enhanced levels of UV -B radiation during a five year period. These species showed reduced AM-fun gal infection percentages in their roots. In C. epigeios AM infection was r educed by 18%, C. arenaria showed a reduction by 20%. The major effect of e nhanced UV-B on AM associations was a reduction of the number of arbuscules . This indicates a reduction in the exchange of nutrients between the symbi onts. Since the effect of UV-B on AM associations may result from altered f lavonoid levels in the root exudates of the host plants, flavonoid levels i n the roots were investigated. No detectable flavonoid concentrations were found in the roots of C. epigeios and C. arenaria. Less effective AM associ ations can have pronounced negative effects on biodiversity and nutrient dy namics of the dune grassland ecosystem. The possible mechanisms causing the se indirect effects of elevated UV-B on below ground AM associations are di scussed. We conclude that UV-B induced changes in plant hormone levels are more likely to be the mechanism reducing AMF infection than UV-B induced al terations in flavonoid concentrations in the root exudates of the host plan t.