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Long-Term Atmospheric CO2 Enrichment Reduces Dark Respiration in Scots Pine
Jach, M.E. and Ceulemans, R.  2000.  Short- versus long-term effects of elevated CO2 on night-time respiration of needles of Scots pine (Pinus sylvestris L.).  Photosynthetica 38: 57-67.

What was done
Three-year old Scots pine (Pinus sylvestris L.) seedlings were rooted in the ground and grown in open-top chambers receiving atmospheric CO2 concentrations of 350 and 750 ppm for two years to determine the short- and long-term effects of elevated CO2 on dark respiration in this important timber species.  In addition, in order to make the experimental results more representative of the natural world, no nutrients or irrigation waters were applied to the soils during this investigation.

What was learned
After two years of differential atmospheric CO2 exposure, seedlings exposed to 750 ppm CO2 displayed significantly lower rates of dark respiration than control seedlings grown in ambient air.  When expressed on a needle mass basis, dark respiration in CO2-enriched seedlings was 27 and 33% lower in current-year and one-year-old needles, respectively.  The greater reductions observed in the older needles was thought to arise from the greater duration of elevated CO2 exposure experienced by those needles.

What it means
As the atmospheric CO2 concentration rises, it is likely that Scots pine seedlings will exhibit significant reductions in respiratory carbon losses.  Since respiration may consume half or more of the atmospheric CO2 fixed during photosynthesis, such reductions in dark respiration -- like those reported in this paper -- can significantly contribute to net carbon gains and ultimately lead to increases in biomass production.  Thus, Scots pine, and other tree species as well, will undoubtedly sequester greater amounts of atmospheric carbon as the CO2 content of the air continues to rise in the future.