Silicon cycled by tropical forest trees: effects of species, elevation and parent material on Mount Kinabalu, Malaysia

Abstract

We aimed to compare uptake and litter flux of silicon (Si) across tropical tree species and sites on Mt. Kinabalu, Borneo. Si flux components were measured at eight plots in tropical forests at four altitudes (700–3,100 m above sea level) on two types of parent materials (acidic sedimentary/granite rock and ultramafic igneous rock, paired at each elevation). Leaf Si concentration differed substantially among tree species (0.24–13.6 mg g−1). Species with high leaf Si concentrations occurred mostly in the lowest elevation plots on both parent materials. The abundance-weighted community means of live-leaf Si concentrations, as well as Si concentration in leaf litter, declined with increasing elevation. Annual leaf-litter Si flux and water extractable Si per unit air-dried soil also decreased with increasing elevation, whereas parent material type had little influence despite consistently higher pH by 0.5–1.0 unit in ultramafic soil. Si uptake and litter Si flux were greater in lower elevation forests regardless of parent material types, most likely because Si accumulating species are more abundant in lowland tropical forests. These results suggest a stronger role of biota than the geochemistry of parent material and rock weathering in Si cycling in the forests on Mt. Kinabalu.