Effects of short-term ozone exposure and soil water availability on the carbon economy of juvenile Douglas-fir.

Effects of ozone and soil water availability on partitioning and translocation of assimilates were studied in three-year-old Douglas-fir (Pseudotsuga menziesii [Mirb.] France) seedlings exposed, in separate experiments, to 0 and 106 or 0 and 514 Fg m-s ozone for 8 h day-’ for 9 days. The dynamics of carbon from assimilated 14C02 were followed. No interactions between ozone and soil water content were observed. Total net uptake of carbon was reduced by low soil water content, but was unaffected by ozone. Both ozone and low soil water content increased the amount of “C-photosynthates retained in the current-year needles. Total starch content in old and current-year needles was unaffected by ozone, but was reduced by low water availability. Translocation of carbon to the root-soil compartment was additively affected by ozone and low soil water content. The results suggest that dry periods in summer combined with high ozone concentrations cause the greatest reduction in the supply of carbon compounds to the root-soil compartment.