Genotypic Differences in Soil Carbon Stocks Under Miscanthus: Implications for Carbon Sequestration and Plant Breeding

Biomass crops provide renewable material for bioproducts and energy generation with the potential for negative greenhouse gas emissions through bioenergy with carbon capture and storage. Miscanthus spp. is a perennial crop with rapid biomass production and low inputs. However, uncertainty exists over impacts on soil organic carbon (SOC) stocks in conversion from agricultural grasslands, and the interaction between divergent Miscanthus species and SOC sequestration. As a C₄ plant (in contrast to C₃ temperate grassland species) the fate of Miscanthus derived carbon can be traced in the soil through its isotopic signature. Taking advantage of this, we use soil cores (pre and post conversion) to investigate species groupings and genotypic effect on SOC stocks in a rare long-term field trial located in the UK. Results show that 10 years after conversion from a managed grass pasture to Miscanthus, expected SOC losses due to cultivation were recovered (Miscanthus spp. mean of 82 Mg C ha⁻¹ compared to pre-conversion stocks of 79 Mg C ha⁻¹, 0–30 cm soil depth) but significant variation in SOC between genotypes was observed (a difference of 32 Mg C ha⁻¹ between the highest and lowest). Of the plant traits investigated, a large rhizome mass was correlated with C₄ carbon, and leaf litter was associated with increased SOC. As well as providing empirical data for the impact on SOC in a likely land use conversion, our findings show a genotypic influence on SOC sequestration processes, revealing the potential of Miscanthus selection to maximise climate mitigation benefits. With only 2 of the 13 genotypes identified as sequestering lower SOC compared to the others, there remains a wide genotypic base to select from. Yield is a primary breeding target (commercially and for increased CO₂ uptake); we demonstrate that high yield need not be at the expense of low soil carbon.