Miscanthus Leaf Drop Timing Impacts Autumn and Winter Soil Decomposition Rates

ABSTRACT

Dedicated biomass crops are widely accepted as an important part of decarbonising economies by producing scalable sources of biomass for energy and renewable bioproducts. Miscanthus is a leading dedicated biomass crop embodying many co‐benefits including soil carbon sequestration. Contributions to carbon balances generally include both high yield (fixed carbon) and ways to limit carbon loss from soils or sequester carbon to soils. Miscanthus inputs carbon to soils via roots, rhizome and leaf litter and one benefit of perenniality is that soil carbon is not disturbed by regular tillage and will potentially accumulate for many years. Variation in over‐winter leaf senescence is highly heritable and leaf litter is relatively easy to assess compared to other tissues contributing to soil carbon that are belowground, making leaf drop an attractive target for breeding. We used data on the genotypic variation in leaf drop in Miscanthus genotypes to simulate different leaf drop profiles. We then used a technique known as the tea bag index to estimate the impacts the identified variation in leaf drop dynamics had on soil decomposition with and without additional nitrogen. The timing of leaf litter treatment had a significant effect on the teabag decomposition rate in the absence of additional nitrogen with treatments in which leaf drop occurred largely over shorter periods resulting in lower decomposition rates. A higher rate often signifies undesirable consequences in that higher CO ₂ emissions occur from the soil. A standard M × giganteus leaf drop profile, a consistent input treatment where the same amount of leaf is applied throughout and control (no litter) all gave worse outcomes. We therefore suggest that leaf drop as a target for breeding can be beneficial for soil carbon sequestration and that under the wet temperate conditions experienced over two years, concentrated leaf drop during winter is the preferable ideotype.