Dissolved organic carbon (DOC) flux is an important mechanism to convey soil carbon (C) from aboveground organic debris (litter) to deeper soil horizons and can influence the formation of stable soil organic C compounds. The magnitude of this flux depends on both infiltration and DOC production rates which are functions of the climatic, soil, topographic and ecological characteristics of a region. Aboveground litter quantity and quality was manipulated for 20 years in an old-growth Douglas fir forest under six treatments to study relationships among litter inputs, DOC production and flux, and soil C dynamics. DOC concentrations were measured at two depths using tension lysimeters, and a hydrologic model was created to quantify water and DOC flux through the soil profile. DOC concentrations ranged from 3.0–8.0 and 1.5–2.5 mg C/L among treatments at 30 and 100 cm below the soil surface, respectively. Aboveground detrital inputs did not have a consistent positive effect on soil solution DOC; the addition of coarse woody debris increased soil solution DOC by 58% 30 cm belowground, while doubling the mass of aboveground leaf litter decreased DOC concentrations by 30%. We suggest that high-quality leaf litter accelerated microbial processing, resulting in a “priming” effect that led to the lower concentrations. Annual DOC flux into groundwater was small (2.7–3.7 g C/m 2 /year) and accounts for < 0.1% of estimated litter C at the site. Therefore, direct DOC loss from surface litter to groundwater is relatively negligible to the soil C budget. However, DOC flux into the soil surface was much greater (73–210 g C/m 2 /year), equivalent to 1.4–2.4% of aboveground litter C. Therefore, DOC transport is an important source of C to shallow soil horizons.

中文翻译：

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太平洋西北原始森林长期凋落物处理下溶解有机碳的产生和通量

溶解有机碳 (DOC) 通量是将土壤碳 (C) 从地上有机碎片（凋落物）输送到更深土壤层的重要机制，并且可以影响稳定土壤有机碳化合物的形成。这种通量的大小取决于渗透率和 DOC 生产率，它们是一个地区的气候、土壤、地形和生态特征的函数。在 6 种处理下对老生长的花旗松森林的地上凋落物数量和质量进行了 20 年的操纵，以研究凋落物输入、DOC 产生和通量以及土壤 C 动态之间的关系。使用张力蒸渗仪在两个深度测量 DOC 浓度，并创建水文模型以量化通过土壤剖面的水和 DOC 通量。DOC 浓度范围为 3.0-8.0 和 1.5-2。在土壤表面以下 30 和 100 厘米处的处理中分别为 5 mg C/L。地上碎屑输入对土壤溶液 DOC 没有一致的积极影响；添加粗木本碎片使地下 30 cm 处的土壤溶液 DOC 增加了 58%，而将地上落叶量增加了一倍，使 DOC 浓度降低了 30%。我们建议优质落叶加速微生物加工，导致“启动”效应导致浓度降低。进入地下水的年 DOC 通量很小（2.7-3.7 g C/m 2 /年），占该地点估计凋落物 C 的 < 0.1%。因此，从地表凋落物到地下水的直接 DOC 损失对于土壤碳收支来说相对可以忽略不计。然而，进入土壤表面的 DOC 通量要大得多（73-210 g C/m 2 /年），相当于 1.4-2。