Leaf elemental composition of species growing on contrasting soils in two adjacent rainforests: Serpentinized ultramafic versus volcano-sedimentary rock

Abstract

The flora of New Caledonia is renowned as one of the world's most significant biodiversity hotpots. The contrasting soil conditions that characterize this small archipelago profoundly influence species local diversity and distribution. Because the difference between soil chemistry is likely to cause variation in leaf elemental composition, we wanted to test how different soil properties affect plant community and leaf elemental concentration. We focused on two adjacent forests, of similar physiognomy, growing on serpentinite (ultramafic rock), and on volcano-sedimentary rock. Both soils strongly differed in their pH, cation exchange capacity, and element concentration (Al, Mn, and Ni). The two adjacent forests have a diverse endemic flora and share a relatively high proportion of species (35%–42%). The tree composition differs more than the total vascular flora. Leaf element concentrations of 30 tree species that grow on both soil types, as well as the corresponding soil–plant-available nutrients, were analyzed. Leaf element concentrations indicated N, P, K, and Ca deficiency. Despite higher plant-available Mn concentration in ultramafic soil than volcano-sedimentary soil, leaf Mn concentrations were significantly higher for plants growing on volcano-sedimentary soil. Leaf Ni concentrations were higher on ultramafic soil and Al concentration was higher on volcano-sedimentary soil. Major differences in leaf elemental concentration were for micronutrients (metals) while macronutrients varied in much lower proportion between the two soil types, suggesting a tight regulation of macronutrients compared to micronutrients.