Plant species differ greatly in their silicon (Si) uptake and accumulation, but little is known about the ecosystem Si cycling in species-rich tropical forest ecosystems. Tropical forest ecosystem processes vary with elevation (climate) and rocks (parent materials), which may interact with each other. Here, we asked how patterns of ecosystem Si cycling differ with elevation and rock type on Mount Kinabalu, the highest peak (4095 m) in Malaysia. At eight permanent plots (0.06 - 1.0 ha) at four altitudes (700, 1700, 2700 and 3100 m a.s.l.) on two geological substrates (Si-rich acidic sedimentary and Si-poor ultrabasic igneous rock) for long-term study of community composition and ecosystem processes, we compared Si concentrations in live leaves of dominant trees (total relative basal area > 60%) and leaf litter (collected from 10 or 20 traps per plot), as well as Si availability from top 10-cm mineral soils (A-horizons) where tree fine roots are most concentrated. Leaf and litter samples were analyzed after alkaline digestion (1% NaCO3) at 85°C overnight, and soil Si availability was determined after shaking in water at room temperature for 20 hours.
Tree species that accumulated Si in leaves were more common at lower elevation sites on both sedimentary and ultrabasic rocks. As a result, the weighted community-wide estimate of Si concentration in live leaves was higher at lower elevation under warmer climate regime (p < 0.001), but did not differ with rock type. Si concentration in leaf litter followed the community-level trend in live leaves, decreasing with increasing in elevation. Si availability in soils (A-horizon) was higher at lower elevation sites on both rocks on Mount Kinabalu. In conclusion, these results strongly suggest that ecosystem Si cycling is more active in lowland forests on both rocks, and that plants significantly modulate ecosystem Si cycling. We quantified Si availability only for A-horizon soil, but because plants may take up Si from deeper soils future study needs to assess Si availability at different soil depth, distinguishing biogenic vs. rock-derived Si.