Smith Lecture: Ecosystem Response to Rising Atmospheric Carbon Dioxide and Ozone: Synthesis of a Long-Term Field Experiment
The accumulation of anthropogenic CO2 in the Earth’s atmosphere, and hence the rate of climate warming, is sensitive to stimulation of plant growth by higher concentrations of atmospheric CO2. In this presentation, I will synthesize data from a long-term, field experiment in which three developing northern forest communities have been exposed to factorial combinations of elevated CO2and O3. Enhanced growth (~26% increase) under elevated CO2was sustained by greater root exploration of soil for growth-limiting N, as well as more rapid rates of litter decomposition and microbial N release during decay. Despite initial declines in forest productivity under elevated O3, compensatory growth of O3-tolerant individuals resulted in equivalent growth under ambient and elevated O3. After a decade, forest growth has remained enhanced under elevated CO2and has recovered under elevated O3by mechanisms that remain un-calibrated or not considered in coupled climate-biogeochemical models simulating interactions between the global C cycle and climate warming.