Photosynthetic pathway, chilling tolerance and cell sap osmotic potential values of grasses along an altitudinal gradient in Papua New Guinea

• Published in: Oecologia 1990-09, Vol.84 (2), p.280-288
• Main Authors: Earnshaw, M.J, Carver, K.A, Gunn, T.C, Kerenga, K, Harvey, V, Griffiths, H, Broadmeadow, M.S.J
• Format: Article
• Language: English
• Subjects: Altitude; Animal and plant ecology; Animal, plant and microbial ecology; Autoecology; Biological and medical sciences; Chlorophylls; cold tolerance; Cooling; Electrolytes; Freezing; frost resistance; Fundamental and applied biological sciences. Psychology; Grasses; Highlands; Low temperature; Lowlands; photosynthesis; Plants; Plants and fungi; Poaceae
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/BF00318285

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 C₃ or C₄ photosynthetic 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 C₄ photosynthesis and were chill-sensitive. The single except ion was Agrostis avenacea, a montane chill-resistant C₃ species 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 C₃ photosynthesis and were chill-resistant. However, an Upland population of the C₄ species, 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).