Climate control of terrestrial carbon exchange across biomes and continents

Understanding the relationships between climate and carbon exchange by terrestrial ecosystems
\nis critical to predict future levels of atmospheric carbon dioxide because of the potential
\naccelerating effects of positive climate–carbon cycle feedbacks. However, directly observed
\nrelationships between climate and terrestrial CO2 exchange with the atmosphere across biomes
\nand continents are lacking. Here we present data describing the relationships between net
\necosystem exchange of carbon (NEE) and climate factors as measured using the eddy
\ncovariance method at 125 unique sites in various ecosystems over six continents with a total of
\n559 site-years. We find that NEE observed at eddy covariance sites is (1) a strong function of
\nmean annual temperature at mid- and high-latitudes, (2) a strong function of dryness at mid- and
\nlow-latitudes, and (3) a function of both temperature and dryness around the mid-latitudinal belt
\n(45◦N). The sensitivity of NEE to mean annual temperature breaks down at ∼16 ◦C (a threshold
\nvalue of mean annual temperature), above which no further increase of CO2 uptake with
\ntemperature was observed and dryness influence overrules temperature influence.