Faculty of Science, Shinshu University, 3-1-1 Asahi, Matsumoto, Nagano, 390-8621, Japan.
Tree Physiol. 2020 Jul 30;40(8):1071-1079. doi: 10.1093/treephys/tpaa051.
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.
植物根系可以向土壤中分泌有机化合物，这些化合物对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，并增强对其他植物入侵的化感作用。我们开发了一种从树木细根中收集小规模碳（C）分泌的方法，即用无碳滤器陷阱。我们在日本一个凉爽的温带森林中，从四个不同微生物共生群（外生菌根（ECM）和丛枝菌根（AM））的针叶树中量化了通过根系分泌的总 C。我们确定了三个直径类别的完整根系（<0.5、0.5-1.0 和 1.0-2.5mm）的质量基础分泌率与形态特征（包括根直径、比根长（SRL）、比根面积（SRA）、根组织密度（RTD）和化学特征（包括根氮（N）含量和 C/N）之间的关系。在物种间，发现质量基础根分泌率与直径、SRA、RTD、N 和 C/N 相关。在比较菌根类型时，在 ECM 物种中，分泌与直径、SRL、SRA、根 N 和 C/N 之间存在显著关系；然而，在 AM 物种中，这些关系并不显著。我们的结果表明，原位根系分泌与形态和化学特征的每一个测量特征之间的关系主要由 ECM 根系驱动，而不是由 AM 根系驱动。这些差异可能解释了这样一个事实，即在这项研究中，ECM 根系通过优化森林树木的分泌和根系形态来潜在地协同作用，而 AM 根系的分泌则不会随根系形态的变化而变化。此外，这种对比结果可能归因于 ECM 和 AM 定殖在细根系统中的程度和位置的影响。这两种菌根的细根分泌与根系形态的关系差异将帮助我们更好地理解森林生态系统中地下碳分配的潜在机制。
