ECOSYSTEM-ATMOSPHERE CO2 EXCHANGE - INTERPRETING SIGNALS OF CHANGE USING STABLE-ISOTOPE RATIOS

Changes in the concentration and stable isotope ratio of atmospheric C O2 can be used to study variations in the net exchange of carbon dioxi de in terrestrial ecosystems (net difference between total photosynthe sis and respiration). Changes in the timing of seasonal fluctuations i n atmospheric CO2 concentration have suggested that net uptake of carb on dioxide has been increasing in northern latitude ecosystems in asso ciation with warmer temperatures and a lengthening of the growing seas on. Stable isotope techniques allow a more detailed separation of diff erences 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 isotop e analyses include documenting and monitoring the influence of global environmental change on ecosystem CO2 exchange at regional scales (10- 1000 km(2)).