Foliar Frost-Resistance of Some Evergreen Tropical and Extratropical Australasian Nothofagus Species

Abstract

Foliar frost resistance was compared in the evergreen Australian Nothofagus species, N. cunninghamii (Hook.) Oerst. and N. moorei (F. Muell.) Krasser, and the New Guinea species, N. carrii Steenis, N. cf. carrii Steenis, N. cf. crenata var. sapeii Steenis, N. grandis Steenis, N. perryi Steenis, N. Pseudoresinosa Steenis and N. pullei Steenis. The order of frost resistance after hardening treatments was N. cunninghamii > N. moorei > New Guinea species, with T₅₀ values (temperature at which 50% tissue damage occurs) ranging from 11.4ºC in N. cunninghamii to -5.7º C in N. grandis and N. cf. crenata var. sapeii. Northern species showed a lower frost resistance than southern species, including N. moorei plants collected from a site with an apparently cooler climate than one population of N. Cunninghamii. The southern species increased in frost resistance by 2.1-3.6º C. N. pullei, N. Pseudoresinosa and N. perryi increased in frost resistance after the hardening regimes by 1.1 -1.5º C, but the other New Guinea species showed no appreciable increase in frost resistance after the artificial hardening regime of 2°C nights and little increase after natural hardening. The results are discussed in relation to the geographic and climatic range of these species.