Contrasting responses to water deficits of Nothofagus species from tropical New Guinea and highlatitude temperate forests: can rainfall regimes constrain latitudinal range?

Results Differences in responses to water deficits between tropical and temperate species appear to reflect differences in climate regimes. In particular, species native to ever-wet rainfall regimes in New Guinea, where water deficits are generally likely to be short-lived, were effective at conserving water by reduced stomatal conductance. In contrast, high-latitude evergreen species on average showed greater development of traits that should enhance water uptake. This was particularly evident in Nothofagus cunninghamii from southern Australia, which developed low water potentials at moderate levels of tissue water deficit and higher root:leaf biomass than tropical species, potentially allowing carbon assimilation to be maximized during warmer, but drier, summer months. However, water relations varied among high-latitude species. In particular, deciduous species on average showed higher rates of conductance, even during moderate levels of tissue water deficit, than evergreen species.