Seminar: Hye In Yang

Release of carbon (C) by plants into soils through rhizodeposition potentially affects the soil microbial activities, including production of enzymes that work on soil organic matter decomposition. It has been shown that elevated atmospheric carbon dioxide (eCO2) can influence soil organic matter turnover by altering belowground plant C allocation. It is hypothesized that trees do this to overcome nutrient limitation. The response of plant and soil processes to eCO2 should accordingly vary with soil nutrient availability. A mesocosm experiment was conducted to investigate how different soil nutrient levels constrain the effect of eCO2 on plant-soil interactions and C turnover. In closed mesocosms, European beech trees (Fagus sylvatica L.) were exposed to ambient and elevated concentrations of CO2 with manipulated 13C label (100 per mille) in order to trace the allocation of newly photosynthesized C in the system and separate plant-derived C from pre-experiment soil organic C. Four nutrient treatments of control (no nutrient addition), nitrogen (N), phosphorus (P), and NP were applied to alter the nutrient availability in the soils. At the end of one growing season, soils and trees were harvested for analysis. Changes in C allocation in above and belowground tree tissues, and consequent shifts in soil microbial activities related to organic matter decomposition under the imposed CO2 and nutrient treatments were explored.