In forest ecosystems, fine root respiration directly contributes to belowground carbon (C) cycling. Exudation from fine roots indirectly affects C cycling via enhanced microbial decomposition of soil organic matter. Although these root-derived C fluxes are essential components of belowground C cycling, how nitrogen (N) addition affects these fluxes and their correlations remains unclear. In this study, fine root exudation, respiration, and chemical/morphological traits were measured in a dominant canopy species, Quercus crispula, found in a cool temperate forest, the Tomakomai Experimental Forest (TOEF), Hokkaido University, which has undergone five-year N addition. Soil-dissolved organic carbon (DOC) was also measured in both bulk and rhizosphere soils to evaluate the impact of fine root exudation on soil C cycling. Compared to a control plot with no N treatment, fine roots in the N addition plot exhibited larger diameters and higher N concentrations, but lower specific root lengths (SRLs) and areas (SRAs). On a root-weight basis, respiration was not different between plots, but exudation was slightly higher under N addition. On a root-area basis, exudation was significantly higher in the N addition plot. Additionally, differences in DOC between rhizosphere and bulk soils were two times higher in the N addition plot than the control plot. Although fine root respiration was positively correlated with exudation in both the control and N addition plots, the ratio of exudation C to respiration C decreased after five-year N addition. N addition also affected absolute C allocation to fine root exudation and changed the C allocation strategy between exudation and respiration fluxes. These findings will help enhance predictions of belowground C allocation and C cycling under N-rich conditions in the future.

中文翻译：

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五年的氮添加会影响日本凉爽温带森林的优势物种栎栎（Quercus crispula）的细根分泌物及其与根呼吸的相关性。

在森林生态系统中，良好的根部呼吸作用直接导致地下碳（C）循环。细根的渗出通过增强土壤有机质的微生物分解而间接影响碳循环。尽管这些根源碳通量是地下碳循环的重要组成部分，但氮（N）的添加如何影响这些通量及其相关性仍不清楚。在这项研究中，对在凉爽的温带森林，北海道大学the小牧实验森林（TOEF）中发现的优势树种Quercus crispula进行了为期5年的测量，测定了优良的根系渗出，呼吸和化学/形态特征。 N加。还测量了块状土壤和根际土壤中的土壤溶解有机碳（DOC），以评估细根分泌物对土壤碳循环的影响。与不进行氮处理的对照地块相比，氮添加地块中的细根表现出较大的直径和较高的氮浓度，但比根部长度（SRL）和面积（SRA）较低。以根重为基础，各样地的呼吸作用没有差异，但是在添加氮的条件下，渗出量略高。以根面积为基础，氮添加区的渗出率明显更高。此外，在氮肥添加区中，根际土壤和散装土壤中DOC的差异是对照区的两倍。尽管在对照和氮添加区中，细根呼吸与渗出均呈正相关，但氮添加五年后，渗出C与呼吸C的比率下降。氮的添加还影响了细根分泌物的绝对碳分配，并改变了渗出和呼吸通量之间的碳分配策略。这些发现将有助于增强对未来氮富集条件下地下碳分配和碳循环的预测。