Transpiration flow controls Zn transport in Brassica napus and Lolium multiflorum under toxic levels as evidenced from isotopic fractionation

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 CO2 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 m2 year1) 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 CO2 ha1 year1 and the flux increased with the level of N fertilization peaking in the 20 g N m2 year1 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.