Nitrogen application increases phytolith carbon sequestration in degraded grasslands of North China

Phytolith‐occluded carbon (PhytOC) has significant potential for long‐term biogeochemical carbon (C) sequestration because of its high resistance against decomposition. It may also play a crucial role in slowing the increase in global CO 2 concentrations and mitigating climate warming. As phytolith C sequestration flux is usually correlated with phytolith content, C content of phytoliths and above‐ground net primary productivity in plants, we hypothesize that application of fertilizers may increase phytolith C sequestration in some degraded grasslands. In this study, we conducted a field experiment to investigate the effects of external application of nitrogen (N) at six levels (0, 10, 20, 30, 40, and 50 g N m −2 year −1 ) from 2011 to 2013 on the potential for phytolith C sequestration in degraded grasslands. Analysis showed that N application increased the PhytOC production flux in the extremely degraded grassland from 0.003 to 0.021 t CO 2 ha −1 year −1 and the flux increased with the level of N fertilization peaking in the 20 g N m −2 year −1 treatment at 700 % of the control flux, but decreased at higher N doses. Assuming half of China's grasslands are fertilized with N to recover from degradation and the phytolith C sequestration flux of degraded grasslands amended with N is half of the 700 % increase, the potential of phytolith C sequestration in China's grasslands could be increased at least 60 %. This study demonstrates that optimization of nutritional supply is a promising approach to increase long‐term phytolith C sequestration in degraded grasslands.