Processes of belowground carbon cycling in the plant-mycorrhiza-soil system as affected by silvicultural management

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With this extention proposal we want to finalize our studies on processes controlling the belowground carbon cycling. In the natural forest, we are comparing carbon allocation in the system plant-soil-atmosphere for different functional types of trees, including Croton macrostachyus, Podocarpus falcatus, and Prunus africana. Within the silvicultural experiments we are focusing on Cupressus lusitanica stands under conventional management and intensive promotion. After whole tree 13C labelling, the labelled carbon will be chased for one year in the leaves, phloem sap, roots and associated microorganisms, and soil and physical soil fractions. This will allow to comparatively investigating the flux of recent assimilates from the plant to the mycorrhiza and soil, and back to the atmosphere, including the separation of autotrophic from heterotrophic soil respiration. As an independent approach, organic carbon transfer from plant to soil, its turnover in the soil, and the source of soil CO2 efflux will be also studied by the 14C approach, including natural abundance and the ‘bomb’ derived 14C. We expect from the results important information on plant-soil organic carbon cycling and storage in soil, and on the consequences of the shift of different functional types of trees due to increasing degradation. For the silvicultural plots, important information on the impact of thinning on the carbon allocation and soil carbon storage can be foreseen.