Distribution of soil phytolith-occluded carbon in the Chinese Loess Plateau and its implications for silica–carbon cycles

Background and aims

Plants absorb and carry soluble silica from soils and then deposit SiO₂?·?nH₂O within themselves producing amorphous silica particles known as phytoliths. Trace amount of organic carbon is occluded during phytolith formation referred to as phytolith-occluded carbon (PhytOC). This carbon fraction has been recognized as an important way of carbon biosequestration. Previous studies have investigated the PhytOC contents of many crop plants and their contribution to global carbon sink. However, the PhytOC in soil is less focused. In this study, we investigated the distribution of soil PhytOC in the Chinese Loess Plateau (CLP).

Methods

Twenty-six soil profiles were collected in the Chinese Loess Plateau. A wet oxidation method was used for phytolith extraction. Occluded carbon was determined by element analyzer.

Results

Our results showed that the soil PhytOC density (SPCD) ranged from 0.757 to 23.110 g/m² among different soil profiles. The SPCD of profiles in the Southern CLP was generally higher than that in the Northern CLP. It was estimated that 5.35 Mt of PhytOC was stored in the upper soil of the CLP. We also estimated the annual phytolith flux into the Yellow River from the CLP by soil erosion and about 2.5 Mt of phytoliths eroded and transported into rivers per year.

Conclusions

Our study indicated that PhytOC was one of the potential biosequestration way and phytoliths had an important influence on biogeochemical cycle of silica. Our results suggested that the soil PhytOC was mainly influenced by different plant communities.