Perennial crops can improve the ecological and economic sustainability of agroecosystems because of their potential to provide diverse ecosystem services including carbon storage. Intermediate wheatgrass (IWG; Thinopyrum intermedium) is a stress-tolerant grain and forage species that can be grown in bicultures with legumes for symbiotic nitrogen fixation that provide additional ecosystem services but also compete with IWG for resources and may diminish field-scale carbon uptake. An eddy covariance (EC) tower was installed in December 2018 in an IWG field in Wisconsin – in which half of the field was frost seeded with red clover (Trifolium pratense L.) – to investigate how perennial grain bicultures and monocultures differ in carbon accumulation compared to monocultures. Using a combination of spatially-partitioned carbon and energy fluxes, collected biomass samples, and harvest and manure estimates, we found that IWG monocultures were larger carbon sinks (–538 to –580 g C m⁻² yr⁻¹) compared to bicultures (–458 to –520 g C m⁻² yr⁻¹), due to greater photosynthetic activity during the growing season and following harvests in August each year. In contrast, evapotranspiration rates were greater in bicultures compared to monocultures (by 0.3–1.4 kg H₂O m⁻² day⁻¹), specifically during summer. Grain and forage harvest resulted in carbon loss which was not recovered until 30 days post-harvest. Carbon loss was greater for bicultures (by 20 g C m⁻² month⁻¹). Net ecosystem carbon balance (NECB) estimates suggested that the IWG monoculture accumulated more carbon (306 ± 88 C m⁻²), whereas the biculture was on average carbon neutral (7 g ± 131 C m⁻²), when biomass removal and manure additions were accounted for. Our study demonstrates the complexities of quantifying carbon budgets in dynamic agricultural systems over short time scales, and the importance of assessing crop multifunctionality within a site's ecological and economic context.

多年生作物可以提高农业生态系统的生态和经济可持续性，因为它们具有提供包括碳储存在内的多种生态系统服务的潜力。中间小麦草（IWG；Thinopyrum intermedium）是一种耐胁迫的谷物和牧草物种，可以与豆科植物进行共生固氮，提供额外的生态系统服务，但也与 IWG 竞争资源，并可能减少田间规模的碳吸收。2018 年 12 月，在威斯康星州的一个 IWG 油田安装了涡流协方差 (EC) 塔，其中一半的田地种有红三叶草（Trifolium pratenseL.) – 研究与单一栽培相比，多年生谷物双栽培和单一栽培在碳积累方面有何不同。结合空间划分的碳和能量通量、收集的生物量样本以及收获和粪便估计，我们发现与双栽培相比，IWG 单一栽培具有更大的碳汇（–538 至 –580 g C m ^-2 yr ^-1）（ –458 至 –520 g C m ^-2 yr ^-1 )，这是由于在生长季节和每年 8 月收获后的光合作用活动更大。相比之下，与单一栽培相比，双栽培的蒸散率更高（0.3-1.4 kg H ₂ O m ^-2天^-1)，特别是在夏天。谷物和草料收获导致碳损失，直到收获后 30 天才恢复。双养殖的碳损失更大（20 g C m ^-2月^-1）。净生态系统碳平衡 (NECB) 估计表明，IWG 单一栽培积累了更多的碳 (306 ± 88 C m ^-2 )，而当生物量去除和粪便处理时，双栽培平均碳中性 (7 g ± 131 C m ^-2 )增加了。我们的研究证明了在短时间内量化动态农业系统中碳预算的复杂性，以及在场地的生态和经济背景下评估作物多功能性的重要性。