Biogeochemical Fluxes for Three Bioenergy Crops

Perennial crops have been the focus of bioenergy research and development for their sustainability benefits associated with high soil carbon (C) and reduced nitrogen (N) requirements. However, perennial crops mature over several years and their sustainability benefits can be negated through land reversion. A photoperiod‐sensitive energy sorghum (Sorghum bicolor) may provide an annual crop alternative more ecologically sustainable than maize (Zea mays) that can more easily integrate into crop rotations than perennials, such as miscanthus (Miscanthus × giganteus). This study presents an ecosystem‐scale comparison of C, N, water and energy fluxes from energy sorghum, maize and miscanthus during a typical growing season in the Midwest United States. Gross primary productivity (GPP) was highest for maize during the peak growing season at 21.83 g C m−2 day−1, followed by energy sorghum (17.04 g C m−2 day−1) and miscanthus (15.57 g C m−2 day−1). Maize also had the highest peak growing season evapotranspiration at 5.39 mm day−1, with energy sorghum and miscanthus at 3.81 and 3.61 mm day−1, respectively. Energy sorghum was the most efficient water user (WUE), while maize and miscanthus were comparatively similar (3.04, 1.75 and 1.89 g C mm−1 H2O, respectively). Maize albedo was lower than energy sorghum and miscanthus (0.19, 0.26 and 0.24, respectively), but energy sorghum had a Bowen ratio closer to maize than miscanthus (0.12, 0.13 and 0.21, respectively). Nitrous oxide (N2O) flux was higher from maize and energy sorghum (8.86 and 12.04 kg N ha−1, respectively) compared with miscanthus (0.51 kg N ha−1), indicative of their different agronomic management. These results are an important first look at how energy sorghum compares to maize and miscanthus grown in the Midwest United States. This quantitative assessment is a critical component for calibrating biogeochemical and ecological models used to forecast bioenergy crop growth, productivity and sustainability.

多年生作物凭借较高的土壤碳（soil carbon, C）含量与较低的氮（nitrogen, N）需求所带来的可持续性优势，长期以来都是生物能源研发的核心关注对象。然而，多年生作物需历经多年方可成熟，且其可持续性优势可能因土地复垦而被抵消。光周期敏感型能源高粱（Sorghum bicolor）可作为一年生作物替代方案，其生态可持续性优于玉米（Zea mays），且与芒草（Miscanthus × giganteus）等多年生作物相比，更易融入作物轮作体系。

本研究针对美国中西部典型生长季内，能源高粱、玉米与芒草的碳（C）、氮（N）、水及能量通量开展了生态系统尺度的对比分析。总初级生产力（Gross Primary Productivity, GPP）在生长旺季以玉米最高，达21.83 g C m⁻² d⁻¹，其次为能源高粱（17.04 g C m⁻² d⁻¹）与芒草（15.57 g C m⁻² d⁻¹）。玉米的生长旺季蒸散量亦为最高，达5.39 mm d⁻¹，能源高粱与芒草分别为3.81 mm d⁻¹与3.61 mm d⁻¹。能源高粱的水分利用效率（Water Use Efficiency, WUE）最高，玉米与芒草的水分利用效率较为接近，分别为3.04、1.75与1.89 g C mm⁻¹ H₂O。玉米的反照率低于能源高粱与芒草（分别为0.19、0.26与0.24），而能源高粱的鲍恩比相较于芒草，更接近玉米（分别为0.12、0.13与0.21）。一氧化二氮（Nitrous Oxide, N₂O）通量方面，玉米与能源高粱分别为8.86 kg N ha⁻¹与12.04 kg N ha⁻¹，显著高于芒草的0.51 kg N ha⁻¹，这一差异反映了三者不同的农艺管理措施。

本研究结果首次系统性对比了美国中西部地区种植的能源高粱、玉米与芒草的各项表现，具有重要的参考价值。此项定量评估可为用于预测生物能源作物生长、产量与可持续性的生物地球化学与生态模型的校准工作提供关键支撑。