Oil-palm and Rainforest Phytoliths Dissolve at Different Rates - with Implications for Silicon Cycling After Transformation of Rainforest Into Oil-palm Plantation

Phytoliths make up the predominant fraction of biogenic silica in plant litter and soils. Thus, they represent a major source of dissolved silicon (Si) in soil-plant systems. Dissolution of phytoliths from Si-accumulating crops such as rice has been well studied in recent years. However, phytolith dissolution in oil-palm plantations remains largely understudied. In this study, we compared dissolution rates of phytoliths isolated from oil-palm fronds, oil-palm litter, and rainforest litter. Our results showed that phytoliths from oil-palm fronds represent an important reservoir of easily dissolvable Si with high dissolution rates (0.44 - 0.69 mg g(-1) d(-1)). Compared to fresh phytoliths from oil-palm fronds, phytoliths isolated from litter showed up to 18 times lower dissolution rates, reflecting silica aging over time. The dissolution rate of phytoliths isolated from rainforest litter (0.067 mg g(-1) d(-1)) was significantly higher than that of phytoliths from oil-palm litter (0.038 mg g(-1) d(-1)). These results demonstrate that transformation of rainforest into oil-palm plantation involves a major change in phytolith production and Si release from litter, considerably altering Si cycling in the soil-plant system. We identified cut-off palm fronds that are usually piled up between the palm rows as most important Si sources maintaining biogeochemical Si cycling in oil-palm plantations.