The data presented below examine the responses of mature branches of Sitka spruce (Picea sitchenis) to elevated CO2 (700 ppmv). This is part of a much larger study of trees, to obtain data that will eventually be used to model the effects of elevated CO2 on tree stands.
Twelve branch bags were designed and installed over branches on the third whorl of six trees in a stand of mature, sixteen-year-old, clonal Sitka spruce. The bags were in place before budburst in 1991. Six further branches on the same trees were as unbagged controls. Six bags received supplementary CO2 (700 ppmv) while the remainder received ambient air.
Leader length of each branch was measured at weekly intervals and used to calculate the branch extension rate. Needle samples were collected at monthly intervals for fresh weight, dry weight, area, chlorophyll (measured spectrophotometrically in DMF), nutrients and Rubisco analysis. Gas exchange (ADC, LCA3) was followed each month measured at growing concentration of CO2 and at the opposite concentration for 1990 and 1991 shoots. The branch and needle dimensions were measured before the bags were installed in April and again in late August.
Leader extension rate was affected by the bags but not by the treatment. During the early part of the season the unbagged (control) branches lagged behind the bagged branches but, by the end of the growing season, all three treatments had similar extension growth. It should be remembered that the primordia determining needle This research was supported by the CEC under the EPOCH programme.