EAGER: Moving Beyond the Leaf Decay Analogy: Root Trait Controls on Decomposition and Soil Carbon Dynamics

植物根的分解还不太清楚。大量的有机碳(C)被结合在根中，而根是植物与土壤相互作用的一部分，吸收养分和水分。并非所有的根都是一样的——它们有各种各样的形状和大小，具有不同的特征和化学成分。该项目将首次测试关于枯死的根如何在土壤中分解、与土壤矿物质相互作用以及促进森林C循环的新想法。将使用一个实验系统来估计地下发生的情况，以便更好地了解根系分解的机制和速率。该项目将为肯特州立大学的本科生和研究生提供培训机会，并通过俄亥俄州科特兰的霍尔顿植物园为小学生提供拓展活动。研究人员还将与肯特州立大学的现有项目（科学学习社区、向上发展和俄亥俄科学与工程联盟）进行协调，以吸引来自大克利夫兰地区的学生，包括那些代表性不足的群体和第一代大学生，他们占肯特州立大学学生总数的46%。了解根系性状如何影响土壤碳动态是在局部和全球尺度上精确的碳建模的关键，因为根系提供了土壤中稳定的大部分碳。然而，尽管根和叶在形态、化学成分和周围环境方面存在明显差异，但目前对根分解的概念化和建模几乎完全基于对叶分解的了解。细根分解发生在与叶片分解根本不同的空间尺度上，导致植物组织、分解者生物以及参与土壤C稳定的矿物和分子机制之间更密切的相互作用。这一建议认为，根系形态是控制分解速率的关键因素，也是植物物种对土壤有机质库有不同影响的原因。分解速率预计会受到根系形态和根系化学性状的影响，因为形态性状控制着微生物定植的表面积和表皮断裂。此外，根系形态可能对根系分解过程中沉积在土壤中的有机质的形式有另一个甚至更大的影响。预测具有细而脆的一级根系的植物物种更容易破碎，直接作为颗粒有机质沉积，可以进一步稳定在土壤团聚体中。相比之下，在分解过程中抗碎裂的粗根预计能维持更大的微生物活性，同时产生溶解有机碳（DOC），并将植物碳转运到周围的土壤中。通过测量代表性状组合梯度的根系质量损失速率，并利用C3和C4植物之间13C特征的差异来追踪根系凋落物衍生的C进入不同的土壤C库，这些假设将通过田间和受控的实验室微观实验进行验证。这项研究将测试一个将根系性状与森林土壤碳动态联系起来的新框架。该框架弥补了土壤中碳稳定的物理矿物学机制和根系特征的分布及其与叶片特征的独立性之间的重要空白。木本丛枝菌根植物是热带和许多温带落叶森林的主要植物类型。如果开发出一个更广泛地包含根系特征的土壤C动力学框架，根系特征的生物地理和系统发育模式将有助于它们在未来建模工作中的应用。

The decomposition of plant roots is not well understood. A significant amount of organic carbon (C) is bound up in roots, and the roots are the part of the plant that interacts with the soil, taking up nutrients and water. Not all roots are the same - they come in a great variety of shapes and sizes, with different characteristics and chemistries. This project will, for the first time, test new ideas about how dying roots are decomposed in soil, interact with soil minerals, and contribute to forest C cycling. An experimental system will be used to approximate what is taking place underground so that the mechanisms and rates of root decomposition can be better understood. The project will involve training opportunities for undergraduate and graduate students at Kent State University, as well as outreach activities for grade school students through Holden Arboretum in Kirtland, OH. Researchers will also coordinate with established programs at Kent State University (Science Learning Community, Upward Bound, and Ohio Science & Engineering Alliance) to attract students from the greater Cleveland area, including those from under represented groups and first-generation college attendees, which make up 46% of the student body at Kent State.Understanding how root traits affect soil C dynamics is key to accurate C modeling at local and global scales because roots provide the majority of C that is stabilized in soil. However, despite obvious differences in morphology, chemical composition and surrounding environment between roots and leaves, root decomposition is currently conceptualized and modeled almost entirely based on what is known about leaf decomposition. Fine root decomposition occurs at a fundamentally different spatial scale than leaf decomposition, resulting in closer interactions between the plant tissue, decomposer organisms, and mineral and molecular mechanisms involved in soil C stabilization. This proposal posits that root morphology is a key control over decomposition rates, and is the reason why plant species have different effects on soil organic matter pools. Decomposition rate is expected to be affected by root morphology, as well as root chemical traits, because morphological traits control surface area as well as breaks in the epidermis available for microbial colonization. Moreover, root morphology likely has another, perhaps even larger, impact on the form of organic matter deposited in soil during root decomposition. It is predicted that plant species with thin and brittle first order roots are more likely to fragment, being deposited directly as particulate organic matter that can become further stabilized inside soil aggregates. By contrast, thick roots that are resistant to fragmentation during decomposition are predicted to sustain greater microbial activity, accompanied by production of dissolved organic C (DOC) and translocation of plant C to the surrounding soil. These hypotheses will be tested using field and controlled laboratory microcosm experiments, by measuring mass loss rates of root systems representing a gradient of trait combinations and by taking advantage of differences in 13C signature between C3 and C4 plants to track root litter-derived C into different soil C pools. This study will test a new framework linking root traits to soil C dynamics in forests. The framework bridges an important gap between emerging information on 1) physical-mineralogical mechanisms by which C is stabilized in soil and 2) the distribution of tree root traits and their independence from leaf traits. Traits are particularly variable for woody arbuscular mycorrhizal plants, a dominant plant type in the tropics and many deciduous temperate forests. Biogeographical and phylogenetic patterns in root traits will facilitate their use in future modeling efforts, if a framework for soil C dynamics is developed that more broadly incorporates root traits.