Spatial variations of soil silicon availability and biogenic silicon flux in a lowland tropical forest in Malaysia

Tropical tree species differ widely in their silicon (Si) accumulation patterns, but the implications of such species differences for ecosystem Si flux remain unexplored. We analyzed how biogenic Si flux via leaf litter and soil Si availability in the upper soil vary spatially within a 2 ha area in a lowland Dipterocarp forest in Peninsular Malaysia. Silicon concentration per unit leaf dry mass of 86 dominant tree species in this plot ranged from 0.4 to 126 mg/g. Soil Si availability at 100 sampling points and Si flux via leaf litter at 66 litter traps showed large variations up to 3.3- and 17.9-folds, respectively. However, they correlated neither with each other nor with the expected Si flux from tree species composition in the neighborhood. When we classified tree species to four groups by their leaf Si concentrations (negligible, low, moderate and high), tree species with moderate leaf Si concentrations were significantly more abundant on Si-rich soils. In contrast, the other three groups did not show any significant spatial relationships with soil Si availability. These results indicate that soil Si availability, Si accumulation by vegetation and Si flux via leaf litter show wide spatial variations in a lowland tropical forest, without a simple relationship with each other.