Climate Control of Terrestrial Carbon Exchange across Biomes and Continents

Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predicate future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate-carbon cycle feedbacks1, 2. However, knowledge of even the broad relationships between climate and terrestrial CO2 exchange with the atmosphere on yearly to decadal scales remains highly uncertain. Here we present data describing net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 132 unique sites including various ecosystems over 6 continents with a total of 583 site-years. With respect to controlling factors we find two distinct groupings of sites: (1) a temperature-limited group where NEE has an exponential relationship with mean annual temperature; and (2) a dryness-limited group where NEE has an inverse exponential relationship with the dryness index7. A strong latitudinal dependence emerges, with 92% of the temperature-limited sites located above 42oN, and 77% of the dryness-limited sites located below 42oN. The sensitivity of NEE to mean annual temperature breaks down at a threshold value of ~16oC, above which no further increase of CO2 uptake with temperature was observed and dryness influence overrules temperature influence. Our findings suggest that (1) net ecosystem carbon exchange is highly limited by mean annual temperature at mid- and high-latitudes, and (2) net ecosystem carbon exchange is highly limited by dryness at low latitudes.JRC.H.2-Air and Climat