Erhöhter ozonstress führt zu erheblicher einschränkung der kohlenstoffbindung in altbuchen - Resümee des "free-air" begasungsexperiments im Kranzberger Forst

Ground-level ozone (O₃) has gained awareness as an agent of climate change. In this respect, key results are comprehended from a unique 8-year free-air O₃ fumigation experiment, conducted on adult beech (Fagus sylvatica) at Kranzberg Forest, Germany. A novel canopy O₃ exposure methodology was employed that allowed whole-tree assessment in situ under twice-ambient O₃ levels. Elevated O₃ significantly weakened the C sink strength of the tree-soil system as evidenced by lowered photosynthesis and whole-stem growth, but increased soil respiration. Associated effects in leaves and roots at the gene, cell and organ level varied from year to year, with drought being a crucial determinant of O₃ responsiveness. Regarding adult individuals of a late-successional tree species, empirical proof is provided first time in relation to recent modelling predictions that enhanced ground-level O₃ can substantially mitigate the C sequestration of forests in view of climate change.