Foliar mineral content of Nothofagus species on ultramafic soils in New Caledonia and non-ultramafic soils in Papua New Guinea

Abstract

Nothofagus species dominate the upper canopy of some New Caledonian rainforests on ultramafic soils. The characteristics of Nothofagus that facilitate its dominance of these forests are uncertain, but may include a superior capacity to resist the severe soil conditions. In this study, we compared foliar concentrations of macronutrients and heavy metals of Nothofagus species from ultramafic soils in New Caledonia with those from non-ultramafic soils in New Guinea. The concentrations of N and P were significantly lower (4–5-fold difference) and Fe, Cr and Ni significantly higher (140–600-fold difference) in the New Caledonian soils than in the New Guinean soils. The magnitude of difference between the two regions in mean foliar mineral concentrations was considerably less. Analysis of the full leaf data set indicated significant differences between the five New Caledonian and five New Guinea species only in P (c. 2.5-fold higher in New Guinean species) and Cr (c. 6-fold higher in New Caledonian species). The absence of significant differences between regions for most foliar elements is associated with leaf : soil ratios (foliar concentration : soil concentration) that show negative correlations with soil mineral-element concentrations. The highest leaf : soil ratios were recorded in New Caledonian species in K and Ca : Mg. The lowest ratios were recorded in the New Caledonian species in Cr, Ni and Fe. There is no evidence of accumulation of heavy metals in the New Caledonian species, with foliar concentrations similar to those of other New Caledonian species growing on non-ultramafic soils. Instead, the limited evidence suggests they are 'excluders'. In general, the New Caledonian Nothofagus species appear to have relatively low foliar concentrations of macronutrients compared with other New Caledonian rainforest species, suggesting that canopy dominance may be in part due to high nutrient efficiency in terms of growth rate per unit nutrient uptake.