Ecosystem-atmosphere CO2 exchange: interpreting signals of change using stable isotope ratios

Changes in the concentration and stable isotope ratio of atmospheric CO2 can be used to study variations in the net exchange of carbon dioxide in terrestrial ecosystems (net difference between total photosynthesis and respiration). Changes in the timing of seasonal fluctuations in atmospheric CO2 concentration have suggested that net uptake of carbon dioxide has been increasing in northern latitude ecosystems in association with warmer temperatures and a lengthening of the growing season. Stable isotope techniques allow a more detailed separation of differences between ecosystem photosynthesis and respiration because these two processes have contrasting effects on both the carbon and oxygen isotope ratio of atmospheric CO2. Future applications of stable isotope analyses include documenting and monitoring the influence of global environmental change on ecosystem CO2 exchange at regional scales (10–1000 km2).