title: Application of heat stress in situ demonstrates a protective role of irradiation on photosynthetic performance in alpine plants.
abstract: The impact of sublethal heat on photosynthetic performance, photosynthetic pigments and free radical scavenging activity was examined in three high mountain species, Rhododendron ferrugineum, Senecio incanus and Ranunculus glacialis using controlled in situ applications of heat stress, both in darkness and under natural solar irradiation. Heat treatments applied in the dark reversibly reduced photosynthetic performance and the maximum quantum efficiency of photosystem II (Fv /Fm), which remained impeded for several days when plants were exposed to natural light conditions subsequently to the heat treatment. In contrast, plants exposed to heat stress under natural irradiation were able to tolerate and recover from heat stress more readily. The critical temperature threshold for chlorophyll fluorescence was higher under illumination (Tc (')) than in the dark (Tc). Heat stress caused a significant de-epoxidation of the xanthophyll cycle pigments both in the light and in the dark conditions. Total free radical scavenging activity was highest when heat stress was applied in the dark. This study demonstrates that, in the European Alps, heat waves can temporarily have a negative impact on photosynthesis and, importantly, that results obtained from experiments performed in darkness and/or on detached plant material may not reliably predict the impact of heat stress under field conditions.
authors.affiliation: Institute of Botany, University of Innsbruck, 6020, Innsbruck, Austria.
authors.forename: Othmar
authors.initials: O
authors.lastname: Buchner
authors.forename: Magdalena
authors.initials: M
authors.lastname: Stoll
authors.forename: Matthias
authors.initials: M
authors.lastname: Karadar
authors.forename: Ilse
authors.initials: I
authors.lastname: Kranner
authors.forename: Gilbert
authors.initials: G
authors.lastname: Neuner
mesh_terms: D003624:Darkness; D006358:Hot Temperature; D008027:Light; D010788:Photosynthesis / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018526:Plant Transpiration / Q000528:radiation effects*; D031947:Ranunculus / Q000502:physiology / Q000528:radiation effects*; D029793:Rhododendron / Q000502:physiology / Q000528:radiation effects*; D012674:Senecio / Q000502:physiology / Q000528:radiation effects*; D024341:Xanthophylls / Q000378:metabolism
chemical_list: D045332:Photosystem II Protein Complex; D024341:Xanthophylls
keywords: CO2-gas exchange; Ranunculus; Rhododendron; Senecio; chlorophyll fluorescence; xanthophyll cycle