Plant roots can exude organic compounds into the soil that are useful for plant survival because they can degrade microorganisms around the roots and enhance allelopathy against other plant invasions. We developed a method to collect carbon (C) exudation on a small scale from tree fine roots by C-free filter traps. We quantified total C through root exudation in four conifers from different microbial symbiotic groups (ectomycorrhiza (ECM) and arbuscular mycorrhiza (AM)) in a cool-temperate forest in Japan. We determined the relationship of mass-based exudation rate from three diameter classes (<0.5, 0.5–1.0, and 1.0–2.5 mm) of the intact root system with root traits such as morphological traits including root diameter, specific root length (SRL), specific root area (SRA), root tissue density (RTD) and chemical traits including root nitrogen (N) content and C/N. Across species, the mass-based root exudation rate was found to correlate with diameter, SRA, RTD, N and C/N. When comparing mycorrhizal types, there were significant relationships between the exudation and diameter, SRL, SRA, root N and C/N in ECM species; however, these were not significant in AM species. Our results show that relationships between in situ root exudation and every measured trait of morphology and chemistry were strongly driven by ECM roots and not by AM roots. These differences might explain the fact that ECM roots in this study potentially covaried by optimizing the exudation and root morphology in forest trees, while exudation in AM roots did not change with changes in root morphology. In addition, the contrasting results may be attributable to the effect of degree and position of ECM and AM colonization in fine root system. Differences in fine root exudation relationships to root morphology for the two types of mycorrhizae will help us better understand the underlying mechanisms of belowground C allocation in forest ecosystems.

中文翻译：

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细根性状对不同菌根协会的四个针叶树原位渗出率的影响。

植物根系可以将有机化合物渗入土壤，这对于植物的生存是有用的，因为它们可以降解根系周围的微生物并增强对抗其他植物入侵的化感作用。我们开发了一种通过无碳滤池从树的细根中收集少量碳（C）渗出物的方法。我们在日本的温带森林中，通过来自不同微生物共生组（切除菌根（ECM）和丛枝菌根（AM））的四个针叶树的根系分泌物，定量了总碳。我们从完整的根系的三个直径类别（<0.5、0.5–1.0和1.0–2.5 mm）确定基于质量的渗出速率与根系特征（例如包括根系直径，比根长（SRL）的形态特征）的关系，特定根区域（SRA），根组织密度（RTD）和化学性状，包括根氮（N）含量和C / N。在整个物种中，发现基于质量的根系渗出速率与直径，SRA，RTD，N和C / N相关。比较菌根类型时，ECM物种的分泌物与直径，SRL，SRA，根N和C / N之间存在显着关系；但是，这些在AM物种中并不重要。我们的结果表明，原位根系渗出与所测形态和化学特性之间的关系受ECM根强烈驱动，而不受AM根强烈驱动。这些差异可能解释了以下事实：本研究中的ECM根系可能通过优化林木的分泌物和根系形态而发生共变，而AM根系的渗出度不会随根系形态的变化而变化。此外，对比结果可能归因于细根系统中ECM和AM定植的程度和位置的影响。两种类型的菌根在精细的根系分泌物与根系形态之间的差异将有助于我们更好地了解森林生态系统地下碳分配的潜在机制。