C: Belowground complexity and carbon dynamics
Problem: The importance of soil as a major carbon (C) sink is acknowledged as paramount amongst ecosystem services: soil contains twice as much C (1550 Pg) compared to the atmosphere (780 Pg) and two to three times more than the amount stored in the vegetation biomass (500-650 Pg) (Lal 2008). While inputs and outputs of C in the above-ground part of forest ecosystems can be recorded continuously with measuring the relevant C-containing gases, and extrapolated from micro- and mezzo-scale to the ecosystem and landscape level, the belowground C processes involved, in particular the dynamics of soil C stocks, are neither easy to monitor nor well investigated and understood. A number of processes are neglected in the ecosystem models, in particular the C input through turnover of fine roots and mycelia of root symbionts - mycorrhizal fungi (Godbold et al., 2006, Brunner and Godbold., 2007; Finer et al, 2007, Cudlin et al, 2007; Wallander et al, submitted). Using 13C techniques, mycorrhizal mycelia turnover was shown to be a dominant process for C input into soil C stocks, contributing more than 60% of new soil C (Högberg et al., 1993; Högberg, 2007; Haberer et al., 2007).  Additionally, C and nitrogen trade-off between plants and mycorrhizal fungi can be assessed using carbon isotope ratios in combination with 15N/14N isotope ratios aiding quantification of mycorrhizal hyphal turnover and its function. While the ectomycorrhizal symbiosis is the predominant mycorrhizal association among the over-storey trees in boreal and northern temperate forests, arbuscular mycorrhizas (AM) becomes increasingly common further south (Opik et al., 2003; 2008; 2009). Due to the asexual nature of Glomeromycota, which are the fungi forming the AM associations, and problems with defining species, the actual number of species capable of forming AM associations is inexact, although some 200 species are currently recognised (Smith and Read, 2008). Human interventions due to climate change, land-use change, and direct application of heavy forest machinery in forestry operations, can contribute to decrease in forest soil macroporosity (>50 μm) up to 50%. Resulting higher water retention and restricted gas exchange lead to decline in mychorrizal and bacteria community structures in soils (Frey et al 2009).
Belowground complexity is therefore a major issue to be studied with respect to climate change, disturbance and air pollution effects on forest ecosystems and their sustainable management.
RID target achievement: Development of protocols to quantify C fluxes in the soil, including mycelial and fine root turnover, development of C dynamics models including the complex belowground diversity, development of an automatic soil respiration measurement system and further development of fine root and mycelial turnover analysis devices with permanent temperature and moisture measurement   
Sub-objectives:
-    C1. Fine root turnover and modelling: database organisation, data analysis and interpretation and their use in modelling belowground carbon dynamics is an imperative for SFI.
-    C2. Mycorrhizal turnover and function: mycorrhiza can give insights in the form of nitrogen taken up, which can provide an insight into the N cycle of plants and its connection to the carbon cycle.
-    C3. Innovative forest management tools to predict consequences of disturbance regimes: Modeling the effects that forest operations and disturbance to biodiversity can have on the capacity of soil to store C
-    C4. Microbial activity & Soil respiration measurements: SFI plans to develop an automatic soil respiration system with chambers at reference plots with measurements of net ecosystem exchange
Collaborative partners involved: PLECO (lead by R. Ceulemans), ZALF (lead by A. Gessler), ULund (lead by H Wallander), UH For (lead by HS Helmisaari), IBAF-CNR (lead by G. Matteucci)

Expected outputs:
-    C1: Innovation in minirhizotron and ingrowth bags measurements of mycelium and fine roots
-    C2: Developed parameterization of a soil module in C flux modeling
-    C3: Developed soil disturbance model for adaptive forest management
-    C4: Innovation in automatic soil respiration devices