title: Altitudinal changes in the incidence of crassulacean acid metabolism in vascular epiphytes and related life forms in Papua New Guinea.
abstract: The occurrence of Crassulacean acid metabolism (CAM), as judged from δ13C values, was investigated in epiphytes and some related plant species at a series of sites covering the approximate altitudinal range of epiphytes in Papua New Guinea. Comprehensive collections were made at each site and the occurrence of water storage tissue and blade thickness was also determined. Some 26% of epiphytic orchids from a lowland rainforest (2-300 m.a.s.l) showed δ13C values typical of obligate CAM and possessed leaves thicker than 1 mm. A second group of orchids, mostly with succulent leaves, possessed intermediate δ13C values between -23 and -26% and accounted for 25% of the total species number. Some species of this group may exhibit weak CAM or be facultative CAM plants. The remainder of the lowland rainforest species appeared to be C3plants with δ13C values between -28 and -35%. and generally possessed thin leaves. Obligate CAM species of orchids from a lower montane rainforest (1175 m.a.s.l) comprised 26% of the species total and mostly possessed thick leaves. The remainder of the species were generally thin-leaved with δ13C values between -26 and -35%. largely indicative of C3photosynthesis. Orchids with intermediate δ13C values were not found in the lower montane rainforest. Obligate CAM appeared to be lacking in highland epiphytes from an upper montane rainforest and subalpine rainforest (2600-3600 m.a.s.l). However the fern, Microsorium cromwellii had a δ13C value of -21.28%. suggesting some measure of CAM activity. Other highland ferns and orchids showed more negative °13C values, up to-33%., typical of C3photosynthesis. The highland epiphytic orchids possessed a greater mean leaf thickness than their lowland C3counterparts due to the frequent occurrence of water storage tissue located on the adaxial side of the leaf. It is suggested that low daytime temperatures in the highland microhabitats is a major factor in explaining the absence of CAM. The increased frequency of water storage tissue in highland epiphytes may be an adaptation to periodic water stress events in the dry season and/or an adaptation to increased levels of UV light in the tropicalpine environment.
authors.affiliation: Department of Cell and Structural Biology, University of Manchester, Williamson Building, M13 9PL, Manchester, UK.
authors.forename: M J
authors.initials: MJ
authors.lastname: Earnshaw
authors.affiliation: Lehrstuhl für Botanik II, Universität Würzburg, Mittlerer Dallenbergweg 64, D-8700, Würzburg, Federal Republic of Germany.
authors.forename: K
authors.initials: K
authors.lastname: Winter
authors.affiliation: Lehrstuhl für Botanik, Institut für Botanik und Mikrobiologie, Technische Universität München, Arcisstrasse 21, D-8000, München 2, Federal Republic of Germany.
authors.forename: H
authors.initials: H
authors.lastname: Ziegler
authors.affiliation: Lehrstuhl für Botanik, Institut für Botanik und Mikrobiologie, Technische Universität München, Arcisstrasse 21, D-8000, München 2, Federal Republic of Germany.
authors.forename: W
authors.initials: W
authors.lastname: Stichler
authors.affiliation: Eastern Highlands Provincial Government, P.O. Box 348, Goroka, Papua New Guinea.
authors.forename: N E G
authors.initials: NE
authors.lastname: Cruttwell
authors.affiliation: Office of Forests, Division of Botany, Department of Primary Industry, P.O. Box 314, Lae, Papua New Guinea.
authors.forename: K
authors.initials: K
authors.lastname: Kerenga
authors.affiliation: Royal Botanic Gardens, Kew, TW9 3AB, Richmond, Surrey, UK.
authors.forename: P J
authors.initials: PJ
authors.lastname: Cribb
authors.affiliation: Royal Botanic Gardens, Kew, TW9 3AB, Richmond, Surrey, UK.
authors.forename: J
authors.initials: J
authors.lastname: Wood
authors.affiliation: Office of Forests, Division of Botany, Department of Primary Industry, P.O. Box 314, Lae, Papua New Guinea.
authors.forename: J R
authors.initials: JR
authors.lastname: Croft
authors.affiliation: Department of Cell and Structural Biology, University of Manchester, Williamson Building, M13 9PL, Manchester, UK.
authors.forename: K A
authors.initials: KA
authors.lastname: Carver
authors.affiliation: Biology Department, Oakham School, Oakham, LE15 6DT, Rutland, Leicestershire, UK.
authors.forename: T C
authors.initials: TC
authors.lastname: Gunn
keywords: Altitude; CAM; Epiphytes; Tropical habitat; δ13C