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

• Applicant: Professor Dr. Christoph Leuschner
• Subject Area: Soil Sciences
• Term: from 2013 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 207213200

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.

• DFG Programme: Research Units
• Subproject of: FOR 1806: The Forgotten Part of Carbon Cycling: Organic Matter Storage and Turnover in Subsoils (SUBSOM)
• Co-Investigator: Dr. Dietrich Hertel