Agroforestry systems that integrate useful long-lived trees have been recognized for their potential in mitigating the accumulation of atmospheric fossil fuel-derived carbon (C). Black walnut (Juglans nigra) is frequently planted and cultivated in North America for its valuable lumber and edible nuts, and is highly amenable to the integration of understory crops or livestock in agroforestry systems. However, little is known about C content in black walnut trees, including the amounts of C assimilated into lignocellulosic tissues within different tree compartments. Therefore, allometric equations for above- and below-ground compartments of 10-year-old black walnut trees across diverse locations were developed. Ten grafted black walnut trees from each of four sites across the midwestern USA were destructively harvested for above- and below-ground biomass, and dry biomass weight (DWw), C (Cw) and nitrogen (N; Nw) stocks were quantified. Soils surrounding the harvested trees were sampled and analyzed for soil organic C (SOC) and total N (TN). Total DWw ranged from 27 to 54 kg tree−1, with woody tissues containing an average of 467 g kg−1 C and 3.5 g kg−1 N. Woody tissues differed in Cw and Nw across location, and above-ground sections contained more C and less N compared with most root tissues. The slopes of the allometric equations did not differ significantly among locations, while intercepts did, indicating that trees only differed in initial size across locations. SOC and TN did not vary in distance from the trees, likely because the trees were not yet old enough to have impacted the surrounding soils. Our results establish a foundation for quantifying C and N stocks in newly established black walnut alley cropping systems across diverse environments.

中文翻译：

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美国密苏里州和阿肯色州四个黑胡桃胡同种植点内的碳和氮积累

整合有用的长寿树木的农林业系统因其在减轻大气化石燃料衍生碳 (C) 积累方面的潜力而得到认可。黑胡桃（Juglans nigra）因其宝贵的木材和可食用坚果而在北美经常种植和栽培，并且非常适合将林下作物或牲畜纳入农林业系统。然而，人们对黑胡桃树中的 C 含量知之甚少，包括不同树间室内同化到木质纤维素组织中的 C 量。因此，开发了不同地点 10 年生黑胡桃树地上和地下隔间的异速生长方程。对来自美国中西部四个地点的每一个地点的十棵嫁接黑胡桃树进行破坏性收获以获取地上和地下生物量，并量化干生物量重量 (DWw)、C (Cw) 和氮 (N; Nw) 种群。对收获的树木周围的土壤进行采样并分析土壤有机碳 (SOC) 和总氮 (TN)。总 DWw 范围为 27 至 54 kg tree−1，木本组织平均含有 467 g kg−1 C 和 3.5 g kg−1 N。木本组织在不同位置的 Cw 和 Nw 不同，地上部分含有更多与大多数根组织相比，C 和更少的 N。异速生长方程的斜率在不同位置之间没有显着差异，而截距有显着差异，这表明树木仅在不同位置的初始大小上有所不同。SOC 和 TN 与树木的距离没有变化，可能是因为树木还不够老，不足以影响周围的土壤。我们的结果为量化不同环境中新建立的黑胡桃胡同种植系统中的 C 和 N 库奠定了基础。