EAR-PF Cracking the Critical Zone: Tree roots in fractures and a proposed mechanistic soil production function

吉尔·马歇尔博士获得了NSF EAR博士后奖学金，将在加州大学伯克利分校与科罗拉多大学博尔德分校合作开展一项研究和教育计划。她将开发数字模型来描述树根对土壤生产的影响。这项研究在临界区科学中的一系列问题上都很重要，从了解景观演变到量化土壤可持续性。调查将使用在三个临界区观测站(鳗鱼河、博尔德溪和南塞拉利昂CZO)收集的数据，这些观测站有成片的地形，土壤薄到没有土壤和基岩裸露。这使得在不同岩性和裂缝模式下的不同地点的裂缝中生长的树根得以定量观察。生物力学土壤生产模型的开发将使人们能够更好地了解植被在土壤可持续性和恢复力中的作用。该教育计划设在加利福尼亚州朗谷(环谷印第安人部落土地所在的鳗鱼分水岭的农村地区)，由两部分组成：针对学区学生的多年龄段实地科学活动和部落自然资源部的激光雷达讲习班。教育计划是在社区的广泛投入下制定的，这些协同活动满足了社区扩大获得科学活动的机会的需求，并为未来的努力提供了工具。本项目的研究将检验以下假设：取决于深度的土壤生产是根压力、根密度随深度的变化以及树木摇摆受岩石性质调制的函数。为了开发描述土壤生产率如何以及为什么随深度变化的地貌运移规律，该项目将结合离散元方法模拟，结合结合颗粒、岩石特性和从三个临界区观测站收集的数据得出的基岩界面上的根压力的现场导出值。将用力传感器监测一套被基岩阻挡的树根，以测量生长产生的外部根压力、树木水分通量产生的日波动，以及风和雪事件产生的围绕树基的扭矩。水文路线、净初级生产力、土壤中的碳储量以及地球化学反应堆的矿物质供应都与土壤生产率有关。通过将树木驱动的过程纳入土壤生产的地貌过程法则，该项目将能够进行数值实验，探索植被的存在和不存在如何控制地表和近地表过程和景观形态。

Dr. Jill Marshall has been granted an NSF EAR Postdoctoral Fellowship to carry out a research and education plan at the University of California, Berkeley, in collaboration with the University of Colorado, Boulder. She will develop numerical models to describe the effect tree roots have on soil production. The investigation is important across a broad range of problems in critical zone science, from understanding landscape evolution to quantifying soils sustainability. The investigation will use data collected at three Critical Zone Observatories (Eel River, Boulder Creek, and Southern Sierra CZOs) that have patches of terrain with thin to no soils and bedrock exposures. This enables quantitative observations of tree roots growing in fractures across sites underlain by different lithologies and fracture patterns. The development of a biomechanical soil production model will allow for improved insight into the role of vegetation in soil sustainability and resilience. The education plan, based in Round Valley, CA (a rural region in the Eel watershed encompassing the Round Valley Indian Tribal Lands) has two components: multi-age field-based science activities directed at the school district's students and a LiDAR workshop for the Tribes' Natural Resource Department. The educational plans were developed with extensive community input and these synergistic activities meet the community's needs of expanding access to science activities and providing tools for future endeavors.Research in this project will test the hypothesis that depth-dependent soil production is a function of root pressures, variations in root density with depth, and tree sway modulated by rock properties. To develop a geomorphic transport law that describes how and why soil production rates vary with depth, this project will combine Discrete Element Method simulations incorporating bonded grains, rock properties, and field-derived values for root pressures at the bedrock interface from data collected at the three Critical Zone Observatories. A suite of bedrock-impeded tree roots will be monitored with force sensors to measure external root pressures generated from growth, diurnal fluctuations due to tree water fluxes, and torque about the tree base from wind and snow events. Hydrologic routing, net primary productivity, carbon storage in soils, and mineral supplies for the geochemical reactor are all linked to rates of soil production. By including tree-driven processes in a geomorphic process law for soil production, this project will enable numerical experiments that explore how the presence and absence of vegetation control surface and near-surface processes and landscape form.