Occluded C in rice phytoliths: implications to biogeochemical carbon sequestration

Carbon (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. 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. Chemical analysis indicates that the phytolith-occluded 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 mg g(-1) to 2.8 mg g(-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 2.37 x 10(8) Mg of CO2 equivalents 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 x 10(7) Mg. Therefore rice crops may play a significant role in long-term C sequestration through the formation of PhytOC.