Biofuel Feedstock Harvest Weakens the Warming-induced Soil Carbon Loss in Grassland Soils

Biofuel feedstock harvest has been proposed as an effective mitigation approach to increase atmospheric CO2 sequestration. The mitigation effect of biofuel remains controversial with little consideration of warming in previous field experiments and modeling studies. Additionally, recent incorporation of microbial communities into ecosystem models has addressed new challenges on metagenomics-informed model parameterization and projection of long-term soil organic carbon (SOC) changes. Here, we conducted a 20-year warming experiment with annual harvest as second factor and evaluated the warming-induced carbon loss as well as the mitigation effect of biofuel feedstock harvest. Our results showed that warming significantly enhanced the heterotrophic respiration by 22% and 16% in unclipped and clipped plots, respectively. Warming also increased gross primary production (GPP) by 3% and 6% without and with clipping. The response of GPP to warming was significantly higher for clipped plots during growing season. The microbial functional genes related to carbon and nitrogen cycles were significantly increased by warming in unclipped plots while no significant changes were observed in clipped sites. The multilevel responses from fluxes to genes were then incorporated into the Microbial-ENzyme Decomposition (MEND) model, showing its high capability to capture the observed patterns in a variety of C-N pool sizes and fluxes. Long-term model projection indicates that warming would cause a SOC loss by 12 ± 4% for unclipped sites and 2± 2% for clipped sites. Further analysis shows that the changed microbial parameters (e.g., enzyme turnover and production rate, microbial maximum growth rate) other than stimulated GPP by clipping is responsible for the weakened warming effect on SOC loss in clipped plots. Our results imply that biofuel feedstock harvest can potentially mitigate greenhouse gas emissions by weakening the warming-induced soil carbon loss in a warming world.