Occluded C in rice phytoliths: implications to biogeochemical carbon sequestration

Aims Caibon (C) bio-sequestration within the phytoliths of plants, a mechanism of long-term biogeochemical C sequestration, may play a major role in the global C cycle and climate change. In this study, we explored the potential of C bio-sequestration within phytoliths produced in cultivated rice (Oryza sativa), a well known silicon accumulator. Methods The rice phytolith extraction was undertaken with microwave digestion procedures and the determination of occluded C in phytoliths was based on dissolution methods of phytolith-Si. Results Chemical analysis indicates that the phytolithoccluded C (PhytOC) contents of the different organs (leaf, stem, sheath and grains) on a dry weight basis in 5 rice cultivars range from 0.4 mgg⁻¹ to 2.8 mgg⁻¹, and the C content of phytoliths from grains is much lower than that of leaf, stem and sheath. The data also show that the PhytOC content of rice depends on both the content of phytoliths and the efficiency of C occlusion within phytoliths during rice growth. The biogeochemical C sequestration flux of phytoliths in 5 rice cultivars is approximately 0.03-0.13 Mg of carbon dioxide (CO₂) equivalents (Mg-e-CO₂) ha⁻¹ year⁻¹. From 1950 to 2010, about 2.37X 10⁸ Mg of CO₂ quivalents might have been sequestrated within the rice phytoliths in China. Assuming a maximum phytoliths C bio-sequestration flux of 0.13 Mg-e-CO₂ ha⁻¹ year⁻¹, the global annual potential rate of CO₂ sequestrated in rice phytoliths would approximately be 1.94×l0⁷ Mg. Conclusions Therefore rice crops may play a significant role in long-term C sequestration through the formation of PhytOC.