ABSTRACT In order to assess the carbon (C) footprint of forest-based bioenergy systems, it is necessary to quantify soil C storage. This study addressed effects of intercropping loblolly pine (Pinus taeda L.) with switchgrass (Panicum virgatum L.) for wood and bioenergy production on soil C storage in coastal North Carolina, USA. Spaces between rows of bedded pine were intercropped with switchgrass or contained native vegetative regrowth after site preparation. Two years after switchgrass establishment, soils were collected from beds and interbeds of each treatment, and C concentration and &dgr;13C were measured in bulk soils and aggregate fractions. Soil C concentration, soil C density (Mg ha−1), and aggregate-associated C were lower in pine beds adjacent to switchgrass compared with pines adjacent to native regrowth. In the greater than 2,000-&mgr;m aggregate size class, 11% of C was derived from new pine inputs in beds of the pine-switchgrass treatment compared to the pine-native treatment. These results indicate that increased belowground C flow in pine beds adjacent to switchgrass may be driving breakdown soil C. In the pine-switchgrass intercropping treatment, a greater percentage of aggregates (by weight and C content) was found in the 2,000- to 250-&mgr;m size class of both beds and interbeds, suggesting that this aggregate size class is sensitive to management. This study provides a baseline analysis of C storage under different management scenarios in pine forests and for investigating long-term (10+ years) impacts. Although presence of switchgrass reduced soil C over the short term, bioenergy intercropping may still be pragmatic from an economical and land-use diversification view point.

中文翻译：

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年轻火炬松种植园的土壤和骨料相关碳

摘要 为了评估基于森林的生物能源系统的碳（C）足迹，有必要量化土壤碳储存。本研究探讨了火炬松（Pinus taeda L.）与柳枝稷（Panicum virgatum L.）间作木材和生物能源生产对美国北卡罗来纳州沿海土壤碳储存的影响。在整地后用柳枝稷间作或包含原生营养再生的层状松树行之间的空间。在柳枝稷建立两年后，从每个处理的床和夹层中收集土壤，并在大块土壤和团聚体部分中测量 C 浓度和 &dgr;13C。与自然再生附近的松树相比，与柳枝稷相邻的松树床中的土壤碳浓度、土壤碳密度（Mg ha-1）和与聚集体相关的碳含量较低。在大于 2 的情况下，000-&mgr;m 聚集体尺寸等级，与松树原生处理相比，11% 的 C 来自松枝柳处理床层中的新松输入。这些结果表明，与柳枝稷相邻的松树床中地下 C 流量的增加可能会导致土壤 C 分解。在松树-柳枝稷间作处理中，在 2,000 至 250- &mgr;m 大小等级的床和夹层，表明该聚集体大小等级对管理敏感。本研究提供了松林不同管理情景下碳储存的基线分析，并用于调查长期（10 年以上）影响。尽管柳枝稷的存在在短期内降低了土壤碳含量，