A BRANCH BAG AND CO2 CONTROL-SYSTEM FOR LONG-TERM CO2 ENRICHMENT OF MATURE SITKA SPRUCE [PICEA-SITCHENSIS (BONG) CARR]

This paper describes the construction and performance of branch bags a nd a CO2 control system used to fumigate branches of mature Sitka spru ce trees with air enriched in CO2 (700 mu mol mol(-1)). It contains so me examples of results obtained using the system over the course of th e first two growing seasons. The branch bags have run continuously for 2 years with very few problems. CO2 concentrations were within 20 mu mol mol(-1) of the target concentration for more than 90% of the time. Temperatures within the bags were slightly higher than ambient (1-2 d egrees C) and this had some effect on phenology. Attenuation of quantu m flux density (photosynthetically active radiation) was 10-15%. The b ranch bag system has enabled investigation into the effects of elevate d CO2 on mature tissue without the problems and expense of fumigating whole trees. Growth in elevated CO2 resulted in an increase in starch and a decrease in soluble protein content of needles. Stomatal conduct ance was higher in elevated CO2 grown needles, and there was some evid ence of an increase in photosynthetic capacity.