SGER: An Experimental System to Study Belowground C Fluxes in Soils

陆地生态系统地下碳库和碳通量在全球变化研究中受到广泛关注。在全球范围内，土壤是一个重要的碳库，其含碳量超过了大气。这一建议侧重于两个涉及地下碳的关键过程，即土壤呼吸和无机碳转化，这两个过程仍然相对知之甚少。这些过程的不确定性在很大程度上源于无法将生物过程（根和微生物呼吸）与非生物过程（气体输送和CaCO3转化）分开，以及难以就地测量根呼吸速率。这些不确定性将通过建立模拟地下呼吸的人工根系来解决。在拟议的项目中，将测试两个假设：1)降水事件后土壤呼吸的短期增加主要受地表微生物过程的调节，因为土壤扩散率、气体位移和根呼吸速率的变化太慢，无法解释现场观察到的快速反应；2)CaCO3的降水和溶解直接依赖于地下生物活动，因此将主要发生在根表面周围。该方案的核心是一种新型的人工根系，它将使用连接到二氧化碳供应的穿孔管来构建。通过调整二氧化碳的流速，根呼吸速率将是固定的和已知的，该SGER奖的更广泛影响包括发展一种新的方法，以获得对地下过程的更好的机制理解，可以应用于与陆地生态学相关的广泛问题。这项研究补充了沙漠研究所正在进行的研究，并将提高其研究能力。该实验系统可以作为教授学生异质环境下气体输运基础知识的重要工具，帮助学生了解生物和物理过程之间的相互作用。将支持一名研究生参与这个项目。

Belowground carbon pools and fluxes in terrestrial ecosystems have received much attention in global change research. Globally, soils are a significant carbon pool containing more carbon than the atmosphere. This proposal focuses on two key processes involving belowground carbon that are still relatively poorly understood, viz. soil respiration and inorganic carbon transformations. Uncertainties with regard to these processes originate, in large measure, from the inability to separate biotic processes (root and microbial respiration) from abiotic processes (gas transport and CaCO3 transformations) and difficulties in measuring root respiration rates in situ. These uncertainties will be addressed by building an artificial root system simulating belowground respiration. In the proposed project two hypotheses will be tested: 1) short-term increases in soil respiration after precipitation events are predominantly regulated by surface microbial processes because changes in soil diffusivity, gas displacement and root respiration rates are too slow to account for rapid responses as observed in the field, and 2) CaCO3 precipitation and dissolution are directly dependent on belowground biological activity and will therefore predominantly occur around root surfaces. The heart of this proposal is a novel artificial root system, which will be constructed using perforated tubing connected to a CO2 supply. By adjusting the flow rate of CO2, the root respiration rates will be fixed and known Broader impacts of this SGER award include the development of a novel approach to obtain a better mechanistic understanding of belowground processes that can be applied to a wide range of questions relevant to terrestrial ecology. The study complements ongoing research at the Desert Research Institute and will enhance its research capabilities. The experimental system can act as an important tool for teaching students fundamentals of gas transport in heterogeneous environments and help students understand the interaction between biological and physical processes. One graduate student will be supported to work on this project.