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，是土壤有机碳的主要来源，是影响根际化学和物理以及土壤容重的媒介，也是将土壤中的水分和养分输送到植物中的植物器官。人们对深层土壤中树根的结构、动态和功能知之甚少。根据第一阶段的细根生物量分布、~(14)C根龄、细根轴向导水率和底土渗出物的原位测定结果，在此阶段，我们研究了不同土壤(酸碱-富碱)上6种山毛榉林下土和表土细根形态、根系动态和根系功能的差异。拟检验的主要假设是：(1)细根分枝程度向下层递减，其中细根表面积(SRA)低于表土根，根组织密度高于表土根；(2)下层根吸收N3-和NH4的能力低于表土根，(3)比根分泌率向下层减少，(4)导管特别大的下层根(高电导率根)比表土根具有更高的表面积吸水率。我们采用了多种原位方法来研究15NO315NH4对矿物质N的吸收能力(方法是在GEüler等人的基础上进行的)。1998)，用微型压力计测量根液通量并将其与细根表面积相关(Senock&Leuschner 1999年后的方法)，测量完整细根的渗出量(Meier等人的方法)。2013)，用微型加速器和图像分析对细根周转率进行量化，用~(14)C-AMS分析估算根龄。寻找山毛榉细根功能分化的证据，表层根系主要吸收N(和其他养分)，下层根系主要负责水分吸收和运输。这应该反映在根的特定吸收能力上。我们提供有关根系动态的数据和估计的根系C输入到底土中，并帮助将底土C周转模型参数化，并接收与根系活动相关的土壤物理和化学条件的数据。

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.