Differences in topsoil and subsoil root morphology and root functioning (water and nitrogen uptake, exudation) of European beech on various bedrock types

根是土壤的重要组成部分，作为SOC的主要来源，作为影响根际化学和物理以及土壤容重的因素，以及作为将水和养分从土壤引导到植物的植物器官。人们对深层土壤中树根的结构、动力学和功能知之甚少。基于第一阶段细根生物量分布，14 C根龄，细根轴向导水率，并在底土原位渗出测量的结果，我们解决在这一阶段的细根形态，根动态和根功能之间的差异，在不同的土壤（酸碱贫碱丰富）在6个山毛榉林底土和表土。试验的主要假设是：（1）细根的分枝程度向下层逐渐减小，下层比细根表面积（SRA）比表层小，根组织密度比表层高;（2）下层根系吸收NO3-和NH 4+的能力低于表层根系;（3）比根系分泌速率向下层逐渐减小，（4）具有特别大导管的底土根（高传导性根）比表土根具有更高的表面比吸水速率。本文采用多种原位方法研究了15 NO3 - 15 NH 4对无机氮的吸收能力（Geßler等人1998年之后的方法），用微型测量器测量根液流量，并将其与细根表面积相关联（根据Senock & Leuschner 1999的方法），以测量完整细根的分泌物（Meier等人2013之后的方法），用微型电子显微镜和图像分析量化细根周转，并用14 C-AMS分析估计根龄。我们寻找的证据表明，细根系统的山毛榉树功能分化的表土根主要吸收功能的N（和其他养分）和底土根主要服务于水的吸收和运输。这应该反映在根系的具体吸收能力上。我们提供根系动态数据和估计的根传C输入到底土中，并帮助参数化底土C周转模型，并接收与根系活动相关的土壤物理和化学条件数据。

Roots are an important component of the soil as a major source of SOC, as agents influencing rhizosphere chemistry and physics as well as the bulk density of the soil, and as plant organs that channel water and nutrients from the soil to the plant. Not much is known about the structure, dynamics and functioning of tree roots in deep soil horizons. Based on the results of the first phase concerning fine root biomass distribution, 14C root age, fine root axial hydraulic conductivity, and in situ exudation measurement in the subsoil, we address in this phase differences in fine root morphology, root dynamics and root functioning between subsoil and topsoil in six beech forests on different soil (acid base-poor to alkaline base-rich). The main hypotheses to be tested are (1) the degree of fine root branching decreases toward the subsoil, where specific fine root surface area (SRA) is lower and root tissue density higher than in topsoil roots, (2) subsoil roots have lower NO3- and NH4+ uptake capacities than topsoil roots, (3) specific root exudation rate decreases toward the subsoil, and (4) subsoil roots with particularly large vessels (high-conductivity roots) have higher surface-specific water uptake rates than topsoil roots. We employ a variety of in situ methods to study the uptake capacity for mineral N using 15NO315NH4 (method after Geßler et al. 1998), to measure root sap flux with miniature gauges and relate it to fine root surface area (method after Senock & Leuschner 1999), to measure the exudation of intact fine roots (method after Meier et al. 2013), to quantify fine root turnover with minirhizotrons and image analysis, and to estimate root age with 14C-AMS analysis. We search for evidence that the fine root system of beech trees is functionally differentiated in topsoil roots with mainly uptake function for N (and other nutrients) and subsoil roots mainly serving in water uptake and transport. This should be reflected in the specific uptake capacities of the roots. We deliver data on root dynamics and estimated root-borne C input into the subsoil and help parameterizing the subsoil C turnover model, and receive data on soil physical and chemical conditions relevant for root activity.