Transformation of Lowland Rainforest into Oil-palm Plantations and use of Fire alter Topsoil and Litter Silicon Pools and Fluxes

The effects of land use and fire on ecosystem silicon (Si) cycling has been largely disregarded so far. We investigated the impacts of land use and fire on Si release from topsoils and litter of lowland rainforest and oil-palm plantations in Jambi Province, Indonesia. Lower concentrations of Si in amorphous silica (ASi) were found in oil-palm plantation topsoils (2.8 +/- 0.7 mg g(- 1)) compared to rainforest (3.5 +/- 0.8 mg g(- 1)). Higher total Si concentrations were detected in litter from oil-palm frond piles (22.8 +/- 4.6 mg g(- 1)) compared to rainforest litter (12.7 +/- 2.2 mg g(- 1)). To test the impact of fire, materials were burned at 300 degrees C and 500 degrees C and were shaken with untreated samples in simulated rainwater for 28 h. Untreated oil-palm topsoils showed a significantly lower Si release (p <= 0.05) compared to rainforest. The fire treatments resulted in an increased Si release into simulated rainwater. Si release from oil-palm topsoils and litter increased by a factor of 6 and 9 (500 degrees C), respectively, and Si release from rainforest topsoils and litter by a factor of 3 and 9 (500 degrees C). Differences between land use were related to initial ASi and litter Si concentrations, and to losses of soil organic matter during burning. We conclude that transformation of rainforest into oil palm plantations could be an important and immediate Si source after a fire event but may indirectly lead to a decrease in the long-term Si availability to plants.