Dissertation Research: Does Hydraulic Redistribution Increase Microbial Activity in the Rhizosphere?

论文研究：土壤水分再分配对土壤微生物活性的影响[j]卡登和P.M.。单株植物的根系可以跨越一定深度的土壤，表现出很强的水分有效性梯度。通常，在干旱地区，表层土壤干燥，深层土壤湿润。这种水可用性的梯度为水通过根系从较深的土壤被动重新分配到营养丰富的浅层土壤提供了动力，这种情况通常发生在夜间。这种“水力再分配”现已在全世界近60个物种中得到认可，并已被证明可以提高蒸腾速率，促进邻近植物的生长，并改变整个地区的水文。一些假设已经出现，集中在水的水力再分配到浅层的潜在重要性，营养丰富的土层，以维持土壤微生物活动，从而潜在地提高植物根系周围的养分有效性。该项目探讨了水力再分配和由此产生的水可用性模式是否会影响根际微生物生物量、生长速率和活动。我们将测试温室和田间的水力再分配是否能增强植物根系周围的养分循环和植物的养分有效性。在美国西部半干旱景观中，深根灌丛蒿属植物（Artemisia tridentata）是一种优势群落。在野外工作中，我们将探讨水力再分配与蒿属植物生殖适宜度之间的关系；在温室中，我们将使用经过基因工程改造的土壤细菌来报告土壤水势，从而首次了解根部周围微毫米尺度的土壤水势。在温室和田间，标准土壤分析和土壤干湿计将用于跟踪微生物活动和土壤湿度。本研究结果将揭示深根三叉蒿影响半干旱系统浅层土壤养分动态和水分含量的机制。

Dissertation Research: Does Hydraulic Redistribution Increase Microbial Activity in the Rhizosphere?Z.G. Cardon and P.M. Herron The root systems of single plants can span a depth of soil exhibiting strong gradients of water availability. Often, in arid regions, dry soils are found at the surface and moister soils at depth. This gradient of water availability provides a driving force for the passive redistribution of water through the root systems from the deeper soils to the shallow, nutrient rich soils, usually at night. Such "hydraulic redistribution" is now recognized in almost 60 species worldwide, and has been shown to increase rates of transpiration, increase growth in neighboring plants, and alter the hydrology of entire regions. A number of hypotheses have emerged focusing on the potential importance of hydraulic redistribution of water into the shallow, nutrient-rich soil layers for maintenance of soil microbial activity, and thus potentially enhanced nutrient availability, around plant roots. This project explores whether hydraulic redistribution, and resulting patterns of water availability, affect rhizosphere microbial biomass, growth rates, and activity. We will test whether nutrient cycling around plant roots, and nutrient availability to plants, are enhanced by hydraulic redistribution in the greenhouse and in the field. The focal plant species is sagebrush (Artemisia tridentata), a deep-rooted shrub that is often a community dominant in semi-arid, western landscapes in the U.S. In field work, we will explore the relationship between the presence of hydraulic redistribution and the reproductive fitness of Artemisia; in the greenhouse, we will use soil bacteria that are genetically engineered to report soil water potentials to provide the first glimpse of soil water potentials at micro- and millimeter scales around roots. In both the greenhouse and the field, standard soil assays and soil psychrometers will be used to track microbial activity and bulk soil moisture. Results from this study will suggest mechanisms by which deep-rooted Artemisia tridentata can affect nutrient dynamics and water contents in shallow soils of semi-arid systems.