Impact of grassland degradation on soil phytolith carbon sequestration in Inner Mongolian steppe of China

Grasslands play an important role in the terrestrial biogeochemical carbon (C) cycle and partly mitigate climate change through C occlusion within phytoliths. Grassland degradation has a significant influence on the coupled biogeochemical cycles of C and silicon in the Inner Mongolian steppe of China, but there are few reports about the impact of grassland degradation on phytolith C sequestration in the steppe, the main grassland in northern China. Twelve sampling sites were chosen in the Xilingol League. Soil samples (0–50 cm) were collected from grasslands of four different degradation degrees to investigate the impact of grassland degradation on the soil phytolith and phytolith-occluded C (PhytOC) accumulation using a mass-balance approach. Soil phytolith storages were 12.97 ± 2.15, 15.90 ± 0.65, 14.35 ± 0.79 and 13.22 ± 1.07 t ha− 1 in non-degraded, lightly degraded, moderately degraded and seriously degraded grasslands, respectively. The corresponding storages of soil PhytOC were 0.11 ± 0.02, 0.16 ± 0.02, 0.12 ± 0.01 and 0.07 ± 0.01 t ha− 1, respectively. The observed significant differences in soil phytoliths and PhytOC among grasslands of different degradation degrees indicate that grassland degradation influenced the phytolith and PhytOC accumulation in grassland soils. Grazing and harvesting are likely the major factors affecting soil phytolith and PhytOC storages through reducing the litterfall returning fluxes. Our preliminary findings imply that grassland restoration could be a promising way to increase long-term phytolith C sequestration through maximizing plant PhytOC production fluxes and soil PhytOC accumulation in degraded grasslands.