Comparison of atmospheric carbon dioxide concentration and metabolic activity in Boreal Forest ecosystems

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Abstract
The increasing seasonal amplitude of atmospheric CO2 concentrations may reflect biotic influences such as increased photosynthesis due to higher CO2 concentrations or increased winter respiration due to warmer temperatures. Boreal forests have a large rôle in the seasonal dynamics of atmospheric CO2 in the Northern Hemisphere, and if terrestrial ecosystems contribute to the greater amplitude, such a signal should appear in the metabolic activity of boreal forests. Analyses in which a mechanistic model of photosynthesis, respiration, and decomposition was driven with the observed annual increase in atmospheric CO2 concentration and observed daily air temperature and precipitation show that from 1974 to 1982 the seasonal amplitude in metabolic activity in boreal forests near Fairbanks, Alaska, increased by 0.52 ± 0.03% year-1. The increasing amplitude was due to increased tree photosynthesis as CO2 concentration increased. However, the increase in annual aboveground biomass production was so small (3 g m-2 year-1 year-1) that it is undetectable given field sampling errors. The small biomass growth increase indicates that a larger seasonal amplitude of atmospheric CO2 can occur without large changes in net primary production, nutrient availability, or nutrient use efficiency. The increase in CO2 concentration that produced the higher biomass production was also small (1.1 ppm year-1), suggesting more attention should be paid to the ecological effects of small changes in CO2 concentrations. DOI: 10.1034/j.1600-0889.1992.t01-2-00002.x