Project Details
Projekt
The architecture of the forest floor and consequences for connectivity
Applicant
Privatdozent Dr. Helmer Schack-Kirchner
Subject Area
Soil Sciences
Forestry
Forestry
Term
since 2022
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 457330647
The organic forest floor (FF), a typical feature of forest soils reveals a strong vertical differentiation in material and morphology with more or less abrupt changes. In soil-survey and site classification purposes this “architecture” of FF and the upper A-horizon is classified as humus form. In case of humus form Moder layered, packed and more or less fragmented foliar litter overlies granular, strongly humified remains of faunal activity covering the mineral soil. Architecture of a forest floor strongly modifies the connectivity for passage of gases, water and nutrients between the atmosphere, mineral soil surface and deeper mineral soil. Although FF-connectivity controls forest-ecosystem matter fluxes data availability and transfer functions in relation to existing humus-form data is fragmentary. In our project we will link the determination of humus form of the 12 research unit experimental sites to soil-physical lab measurements by an innovative microtopographical-photogrammetric assessment of the architecture. This method yields high-resolution digital surface models of the different layers from which precise information about thickness, volume, and inner structure can be derived. We will implement on all sites two types of microtopographical plots. First, 50*50 cm permanent plots which are assessed over three vegetation periods to yield the integral temporal height dynamic of FF. Second, 20*20 cm small plots where we get 3-dimensional FF models by successive sampling of the different FF layers and the precise bulk volume of the sampled material. FF is also sampled with preserved natural structure for soil physical lab measurements of water retention, water permeability, ionic diffusivity, and gas diffusion. Depth profiles of CO2, N2O, and CH4 will be analyzed. Iron-oxide coated glass plates are deployed for some weeks to assess vertical patterns of reductive mobilization. Both methods allow an ecological interpretation of soil physical features connected to aeration and water retention, such as release of dissolved organic carbon or exchange of greenhouse gases. Based on the state of knowledge and in close connection to the other research-unit partners we will test following hypotheses. (1) Sharp transitions between layers and coarse structural elements within layers cause capillary barriers (2) Reduced capillary continuity cause seasonal contrasts of water saturation and aeration (3) Morphology of FF is temporarilly dynamic which influences also connectivity of FF to the mineral soil. This dynamic can be assessed by microtopographical modelling. (4) In moist periods low-connectivity FF reveals reductive microsites leading to a reductive mobilization of iron, higher N2O and CH4 concentrations, and mobilization of dissolved organic carbon.
DFG Programme
Research Units
Co-Investigator
Professorin Dr. Friederike Lang
