, Volume 89, Issue 1, pp 43-60
Date: 13 Jul 2007

Measurement of net ecosystem exchange, productivity and respiration in three spruce forests in Sweden shows unexpectedly large soil carbon losses

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Abstract

Measurement of net ecosystem exchange was made using the eddy covariance method above three forests along a north-south climatic gradient in Sweden: Flakaliden in the north, Knottåsen in central and Asa in south Sweden. Data were obtained for 2 years at Flakaliden and Knottåsen and for one year at Asa. The net fluxes (Nep) were separated into their main components, total ecosystem respiration (Rt) and gross primary productivity (Pg). The maximum half-hourly net uptake during the heart of the growing season was highest in the southernmost site with −0.787 mg COm−2 s−1 followed by Knottåsen with −0.631 mg COm−2 s−1 and Flakaliden with −0.429 mg COm−2 s−1. The maximum respiration rates during the summer were highest in Knottåsen with 0.245 mg COm−2 s−1 while it was similar at the two other sites with 0.183 mg COm−2 s−1. The annual Nep ranged between uptake of −304 g C m−2 year−1 (Asa) and emission of 84 g C m−2 year−1 (Knottåsen). The annual Rt and Pg ranged between 793 to 1253 g C m−2 year−1 and −875 to −1317 g C m−2 year−1, respectively. Biomass increment measurements in the footprint area of the towers in combination with the measured net ecosystem productivity were used to estimate the changes in soil carbon and it was found that the soils were losing on average 96–125 g C m−2 year−1. The most plausible explanation for these losses was that the studied years were much warmer than normal causing larger respiratory losses. The comparison of net primary productivity and Pg showed that ca 60% of Pg was utilized for autotrophic respiration.