title: Ecological trends in lichen photosynthesis.
abstract: Drawing on data for 42 fruticose and foliose lichen species, four aspects of photosynthetic response have been ex&mined in relation to latitude and climatic variables: 1) the maximal rate of net photosynthesis (Pmax), 2) the tissue temperature at which Pmaxoccurs (Topt), 3) the photon flux density at which Pmaxoccurs (PhARsat), and 4) the tissue water status at which Pmaxoccurs. Tissue water status was measured as either relative water content (RWCopt) or percentage dry weight (DWopt). The Toptdecreased significantly with increasing latitude; Toptalso increased significantly with increasing July solar radiation, July air temperature, daily hours of bright sunshine, daily solar radiation, annual precipitation, and annual evaporation. Both RWCoptand DWoptincreased significantly with annual precipitation. The Toptand RWCoptfor a lichen could both be more accurately predicted from multiple regressions on macroclimatic variables describing the lichen's habitat. Both the PhARsatand the Pmax, despite their lack of simple univariate relationships to either latitude or climatic variables, could also be predicted by multiple regression. The limitations on the generality and precision of these ecological trends in lichen photosynthesis are discussed in relation to microclimatic considerations, morphological adaptations, and poikilohydric metabolism.
authors.affiliation: Department of Biology, McGill University, 1205 Avenue Docteur Penfield, H3A 1B1, Montreal, Quebec, Canada.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Lechowicz