The influence of deciduous tree species on soil carbon dynamics and sequestration in temperate forests

• Applicant: Dr. Christina Steffens
• Subject Area: Soil Sciences
• Term: from 2015 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 271082204

Temperate forests store 300 billion tons of organic carbon (C). In Europe, 800 million tons of C are fixed annually in the forest, ~40% in the soil and ~60% in the living biomass. One goal of sustainable forestry is to ensure and increase the C sink function of the forest ecosystem. However, the factors controlling this process are not yet fully understood. The main objective of the proposed study is to analyze the effect of important tree species (Fagus sylvatica L., Quercus spec., Fraxinus excelsior L., Acer pseudoplatanus L., Tilia cordata Mill. and Picea abies L. Karst.) on forest C-sequestration. The study will address the following specific objectives:(1) While the tree species effect on soil C stocks is well documented, the change in soil C stocks over time, i.e. the C sequestration, remains largely unknown. In the present study, the forest soil will be resampled for soil C under different tree species in Danish common garden experiments which were analyzed for C 10 years ago in 2004/2005. Thus, possible changes in soil C stocks can be directly quantified. (2) It remains unclear which mechanisms are responsible for the tree species effect on forest soil C stocks and stock changes. Thus, soil respiration will be measured over two years and partitioned into its sources, the heterotrophic respiration (decomposition of organic substances) and the autotrophic respiration (root respiration). It will be checked whether the relative proportions of these sources to the total soil respiration are dependent on tree species and thus contribute to different carbon stocks in the forest floor.(3) In previous studies of tree species effects, differences in C stocks were observed either in the soil or in the biomass. However, it is possible that differences between species in soil and biomass C stocks are not positively related to each other, i.e. the available studies do not allow drawing conclusions concerning a total tree species dependent C-balance of the forests. Furthermore, the trace gases nitrous oxide (N2O) and methane (CH4) are relevant greenhouse gases, too, as their warming potentials are 28 times (CH4) and 264 times (N2O) higher than that of CO2, respectively. Tree species may influence the N2O emission and CH4 uptake in a different way than the CO2 emission. In the present study the total greenhouse gas balance (biomass and soil) including the CH4 uptake and N2O emissions will be quantified at the tree species level over a period of two years.Additional soil properties, e.g. nutrient content, will be analyzed in order to enable calibration and validation of existing biogeochemical models (e.g. Biome-BGC, Version Zalf) in a follow-up project to be pursued subsequent to this funding period.

• DFG Programme: Research Grants