Bioenergy crop Miscanthus x giganteus acts as an ecosystem engineer to increase bacterial diversity and soil organic matter on marginal land

Cultivation of the bioenergy and bioproduct crop Miscanthus x giganteus (Miscanthus) on marginal lands (including those that are anthropogenically damaged) is attractive due to the robust growth of Miscanthus, leading to high yields even under stressful environmental conditions. Miscanthus growth and production may also build soil carbon, which is favorable for land restoration and climate change mitigation. Gaps in our understanding of the mechanisms facilitating soil carbon accumulation under Miscanthus persist, particularly regarding the role of the soil microbiome in facilitating these processes, and how land use histories (e.g. past disturbances) and management strategies (e.g., fertilizer additions) affect these mechanisms. To address these knowledge gaps, we measured plant performance, soil properties, and microbial parameters over the first three years of Miscanthus establishment across a gradient of disturbance intensity and different fertilization strategies (none, organic, conventional). We determined that plant performance (e.g., aboveground biomass yield) and microbial carbon use efficiency (CUE) increased over time during establishment under all disturbance intensities but remained lower overall at the most intensely disturbed site. Across all sites, bacterial diversity and microbial carbon use efficiency increased over time and were positively correlated with soil organic matter. We also observed increases in the relative abundance of key plant growth promoting microbes (e.g., mycorrhizal fungi and bacterial N-fixers). There was no effect of nutrient addition on plant yield, soil carbon concentrations, or microbial carbon cycling. All told, our results suggest that Miscanthus consistently increases microbial diversity and carbon use efficiency, facilitating soil organic matter accumulation across sites despite varying land use histories and soil properties. In this way Miscanthus acts as an ecosystem engineer, improving soil biological and chemical properties such that highly disturbed soils come to resemble less disturbed systems over time.