Uncertainty in soil carbon (C) fluxes across different land‐use transitions is an issue that needs to be addressed for the further deployment of perennial bioenergy crops. A large‐scale short‐rotation coppice (SRC) site with poplar (Populus) and willow (Salix) was established to examine the land‐use transitions of arable and pasture to bioenergy. Soil C pools, output fluxes of soil CO₂, CH₄, dissolved organic carbon (DOC) and volatile organic compounds, as well as input fluxes from litter fall and from roots, were measured over a 4‐year period, along with environmental parameters. Three approaches were used to estimate changes in the soil C. The largest C pool in the soil was the soil organic carbon (SOC) pool and increased after four years of SRC from 10.9 to 13.9 kg C m⁻². The belowground woody biomass (coarse roots) represented the second largest C pool, followed by the fine roots (Fr). The annual leaf fall represented the largest C input to the soil, followed by weeds and Fr. After the first harvest, we observed a very large C input into the soil from high Fr mortality. The weed inputs decreased as trees grew older and bigger. Soil respiration averaged 568.9 g C m⁻² yr⁻¹. Leaching of DOC increased over the three years from 7.9 to 14.5 g C m⁻². The pool‐based approach indicated an increase of 3360 g C m⁻² in the SOC pool over the 4‐year period, which was high when compared with the −27 g C m⁻² estimated by the flux‐based approach and the −956 g C m⁻² of the combined eddy‐covariance + biometric approach. High uncertainties were associated to the pool‐based approach. Our results suggest using the C flux approach for the assessment of the short‐/medium‐term SOC balance at our site, while SOC pool changes can only be used for long‐term C balance assessments.

中文翻译：

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短轮伐木场的土壤碳和地下碳平衡：三种不同方法的评估。

不同土地利用过渡过程中土壤碳（C）通量的不确定性是一个问题，需要进一步部署多年生生物能源作物。建立了一个由杨树（Populus）和柳树（Salix）组成的大规模短轮伐木场（SRC），以研究耕地和牧场向生物能源的土地利用转变。土壤碳库，土壤CO ₂，CH _4的输出通量，在4年的时间内测量了溶解有机碳（DOC）和挥发性有机化合物，以及凋落物和根部的输入通量以及环境参数。三种方法可用来估算土壤碳的变化。土壤中最大的碳库为土壤有机碳（SOC）库，SRC四年后从10.9 kg C m ^-2增加到13.9 kg C m ^-2。地下木质生物量（粗根）代表第二大碳库，其次是细根（Fr）。一年生叶落是土壤中最大的碳输入，其次是杂草和Fr。第一次收获后，我们观察到很高的Fr死亡率将大量的C输入土壤。随着树木的长大和长大，杂草的投入减少。平均土壤呼吸强度为568.9 g C m ^-2 yr ^-1。三年中，DOC的浸出量从7.9 g C m ^-2增加到14.5 g C m ^-2。基于池的方法表明，SOC库在4年期间增加了3360 g C m ^-2，与基于通量的方法估计的-27 g C m ^-2和- 956 g C m ^-2的涡旋-协方差+生物特征学方法的组合。高度不确定性与基于池的方法相关。我们的结果建议使用C流量法评估我们站点的中短期SOC平衡，而SOC池变化仅可用于长期C平衡评估。