Sequestration potential of phytolith occluded carbon in China's paddy rice (Oryza sativa L.) systems

Phytolith-occluded carbon (PhytOC) is resistant to decomposition and, if crop residue biomass is incorporated into soil, has a significant potential for long-term soil carbon sequestration. However, the magnitude and spatial distribution of rice straw PhytOC sequestration remain unclear. Here, we used 279 samplings from nine provinces across China to establish the relationship between soil nutrients availability and rice straw phytoliths concentration, thereby predicting annual PhytOC sequestration of Chinese rice systems. The results suggest that rice straw phytoliths sequester about 0.26 Tg CO2 per yr (8.7 kg CO2 ha−1 yr−1) in China. Great variability of PhytOC exists across the region depending on rice variety. If rice varieties that occluded little PhytOC were replaced by ones with the highest PhytOC concentration, the sequestration rate might be increased to 0.83 Tg CO2 yr−1 (27.7 kg CO2 ha−1 yr−1). The distribution pattern shows that 51% of rice straw PhytOC sequestration can be attributed to the Middle-Lower Yangtze Plain due to its vast rice production. PhytOC sequestration is a crucial mechanism of global biogeochemical carbon sink, and practices such as appropriate fertilization application and selection of rice varieties with higher PhytOC concentration may alleviate climate warming.