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

Abstract

The increasing seasonal amplitude of atmospheric CO 2 concentrations may reflect biotic influences such as increased photosynthesis due to higher CO 2 concentrations or increased winter respiration due to warmer temperatures. Boreal forests have a large role in the seasonal dynamics of atmospheric CO 2 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 CO 2 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 CO 2 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 CO 2 can occur without large changes in net primary production, nutrient availability, or nutrient use efficiency. The increase in CO 2 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 CO 2 concentrations. DOI: 10.1034/j.1600-0889.1992.t01-2-00002.x