Coniferous forest ecosystems are important pools of soil organic carbon (SOC) in the Northern temperate zone. Needle leachates and root exudates represent a significant input of C to these soils and can differently affect soil C cycling because of their differences in chemistry and stoichiometry. This is the first study to investigate the differences in the flow of dissolved organic C (DOC) in the form of needle leachates, root exudates, and their combination through a forest mineral topsoil. We conducted a 5-month microcosm experiment with ecologically relevant additions of ¹³C-labelled spruce-derived substrates. The proportion of DOC lost from or incorporated into the mineral soil as microbial biomass or soil fractions (free, occluded by or adsorbed onto mineral particles) as well as differences in the priming effect (PE) caused by the two substrates were assessed.

Needle leachates (higher in phenolics and C:N ratio) were less utilized by the microbial community than root exudates but caused a higher PE probably because they lacked sufficient N to satisfy microbial N demands. The addition of either substrates failed to change microbial community composition or SOC content in soil fractions. Most of the substrate C in soil fractions was stabilized by adsorption onto mineral particles. On average, 69% of the substrate C was lost via mineralization; only 0.23% via leaching. The most important C pool related to substrate C gain was the C stored in soil fractions (29%); only 1.7% was stored in the microbial biomass. A consideration of all C gains and losses indicates that the addition of spruce-derived substrates resulted in an average net substrate C retention of 31%.

针叶林生态系统是北温带重要的土壤有机碳 (SOC) 库。针浸出液和根系分泌物代表了这些土壤中碳的重要输入，并且由于它们在化学和化学计量方面的差异，可以不同地影响土壤碳循环。这是第一项研究以针浸出液、根系分泌物及其组合形式通过森林矿物表土的溶解有机碳 (DOC) 流量差异的研究。我们进行了为期 5 个月的微观实验，其中添加了¹³C 标记的云杉衍生底物。评估了作为微生物生物量或土壤组分（游离、被矿物颗粒吸留或吸附在矿物颗粒上）从矿物土壤中损失或并入矿物土壤中的 DOC 的比例以及由两种基质引起的引发效应 (PE) 的差异。

与根系分泌物相比，针浸液（酚类物质和 C:N 比率较高）被微生物群落利用较少，但导致较高的 PE，可能是因为它们缺乏足够的 N 来满足微生物对 N 的需求。添加任何一种底物都未能改变土壤组分中的微生物群落组成或 SOC 含量。土壤组分中的大部分底物 C 通过吸附到矿物颗粒上而稳定。平均而言，69% 的底物 C 通过矿化流失；通过浸出仅 0.23%。与底物碳增加相关的最重要的碳库是储存在土壤组分中的碳 (29%)；只有 1.7% 储存在微生物生物量中。考虑所有 C 的增加和损失表明，添加云杉衍生底物导致平均净底物 C 保留率为 31%。