Seminar: Kristian Schufft

Increasing atmospheric CO2 concentrations will lead to higher photosynthetic carbon uptake in forests. However the actual long-term carbon sink capacity,especially in old, mature forests, is strongly inhibited by nutrient limitation. Instead of growth plants might transport additional sequestrated carbon into soils to enhance nutrient acquisition.

A CO2 experiment study froma mature, P-limited forest in Australia (EucFACE) suggests that over 50% of additional photosynthetically fixed carbon is not stored in biomass but transported belowground (root exudation) where it increases soil respiration and affects microbial activity. We implemented a mechanism for dynamic root exudation into a microbial-explicit terrestrial biosphere model to understand the effect of increased root exudation induced by elevated CO2. We evaluated the model against the EucFACE carbon budget and investigated the effect of additional C transported into soils on microbial nutrient cycling, potential priming activity and plant feedback. We found that than 50% of fresh root exudates get directly respired while the rest accelerates nutrient and carbon cycling. We observe no strong net effect of eCO2 on old SOM but our simulations suggest a faster turnover of this pool.