Do elevated ozone and variable light alter carbon transport to roots in sugar maple?

• Here we conducted a series of14C pulse-chase labeling experiments to test the hypothesis that ozone reduces allocation of recently assimilated carbon to roots of sugar maple (Acer saccharum). • Sugar maple seedlings were fumigated with 1.0 ×, 1.7 × and 3.0 × ambient ozone in open-top chambers for 3 yr under low and high light. Shoots were labeled with14CO2for 1 h in August of year 3, and seedlings were harvested 0, 4, 24 and 48 h after labeling. • Three years of ozone fumigation reduced total biomass of seedlings in low and high light treatments by 49% and 34%, respectively, and reduced per cent allocation of total seedling biomass to roots. Ozone similarly reduced allocation of net14C (gross14CO2assimilated at time = 0 minus respiratory losses) to roots after 48 h, but not gross14C, despite significant ozone effects on14CO2assimilation, leaf-level partitioning, and retention of gross carbon in shoots. • Although ozone delayed transport of14C out of leaves initially, it had no effect on the transport process per se. Any reduction in net allocation to roots is most likely a function of changes in whole-plant source-sink relationships, with control a function of both shoot and root traits.