A framework linking silicon fertilisation, plant silicification and soil carbon cycling

Societal Impact Statement: Soil organic carbon (SOC) is vital for soil health, food security and climate change mitigation. We reviewed how silicon (Si) fertilisers, commonly used to improve plant health, may also influence SOC dynamics. We developed a framework linking Si and SOC and discussed the possibility of Si-mediated plant changes contributing to SOC sequestration. We highlight that Si fertilisation is a potential strategy to reconcile the contradiction between intensive agriculture and the need to sequester carbon, supporting both productivity and decarbonisation goals. Summary: The quantity and quality of plant C inputs to soil significantly influence decomposition and stabilisation processes which primarily affect the dynamics of soil organic carbon (SOC). Si has emerged as an important element for improving plant performance, which in turn affects the quantity and quality of such plant C inputs. Research on the interaction between Si and plant biochemical processes highlights a trade-off between Si and C. Additionally, Si alters plant stoichiometry and belowground C allocation by promoting nitrogen (N) and phosphorus (P) use efficiency, potentially impacting C cycling in rhizosphere processes. However, these processes have not been thoroughly understood to date, limiting our understanding of the role of Si in soil C cycling. This review synthesises existing literature to advance the understanding of plant silicification in soil C cycling. For the first time, we propose a framework linking plant silicification and soil C cycling, via two pathways. First, Si affects C cycling during plant litter decomposition by altering plant chemical composition. We hypothesise that Si-mediated changes in stoichiometry and C quality reduce litter stability and accelerate processing by the soil community, ultimately promoting SOC stabilisation. Second, Si-enhanced plant nutritional status may alter belowground C allocation, impacting rhizosphere C cycling. We expect that plant silicification would reduce native rhizosphere SOC loss by the rhizosphere priming effect, as improved plant nutritional status results in less belowground C allocation for resource acquisition. We consider that Si fertilisation could contribute to maintaining soil health, particularly in agricultural systems.