| 英文摘要: | 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. |