title: Photosynthetic pathway, chilling tolerance and cell sap osmotic potential values of grasses along an altitudinal gradient in Papua New Guinea.
abstract: A total of 22 grass species were examined from 5 sites spanning the altitudinal range 1550-4350 m.a.s.l. The presence of the C3or C4photosynthetic pathway was determined from δ13C values and chilling tolerance was assessed on the basis of electrolyte leakage from leaf slices incubated on melting ice. Most of the grasses studied at the lower altitude sites of 1550 m.a.s.l. (annual mean of daily minimum temperature, 14.6° C) and 2600 m.a.s.l. (9.4° C) possessed C4photosynthesis and were chill-sensitive. The single except ion was Agrostis avenacea, a montane chill-resistant C3species which occurred at 2600 m.a.s.l. The three species apparently most sensitive to chilling were Ischaemum polystachyum, Paspalum conjugatum and Saccharum robustum, all occurring at 1550 m.a.s.l. At the higher altitude sites of 3280 (5.6° C), 3580 (4.0° C) and 4350 (-0.7°C) m.a.s.l., most of the grasses exhibited C3photosynthesis and were chill-resistant. However, an Upland population of the C4species, Miscanthus floridulus was found at 3280 m.a.s.l. which had acquired chill-resistance as confirmed by additional in vivo variable chlorophyll fluorescence measurements. Cell sap osmotic potential values of the upland grasses at altitudes of 3280-4350 m.a.s.l. were lower (-8.1 to -19.8 bars) than values in grasses from 1550 and 2600 m.a.s.l. (-3.9 to -7.5 bars) due mainly to the presence of non-electrolyte osmoticants, which may be involved in frost avoidance mechanism(s).
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: 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
authors.affiliation: Division of Botany, Department of Primary Industry, Office of Forests, P.O. Box 314, Lae, Papua New Guinea.
authors.forename: K
authors.initials: K
authors.lastname: Kerenga
authors.affiliation: Biology Department, Oakham School, Oakham, LE15 6DT, Rutland, Leicestershire, UK.
authors.forename: V
authors.initials: V
authors.lastname: Harvey
authors.affiliation: Department of Biology, The University, NE1 7RU, Newcastle upon Tyne, UK.
authors.forename: H
authors.initials: H
authors.lastname: Griffiths
authors.affiliation: Department of Biology, The University, NE1 7RU, Newcastle upon Tyne, UK.
authors.forename: M S J
authors.initials: MS
authors.lastname: Broadmeadow
keywords: Altitude; C3/C4 photosynthesis; Chilling tolerance; Frost hardiness; Tropical habitat