INFLUENCE OF FOLIAR N ON FOLIAR SOLUBLE SUGARS AND STARCH OF RED SPRUCE SAPLINGS EXPOSED TO AMBIENT AND ELEVATED OZONE

Red spruce (Picea rubens Sarg.) trees growing at high elevation in the northeastern United States have experienced decline in recent years b ut seedlings have proved to be relatively tolerant of a wide range of environmental stresses in controlled studies. One possible reason for the wide tolerance to stress in seedlings is their inherently large po ol of carbohydrate reserves, which is available for maintenance during and regrowth after periods of stress. We tested for the effects of fo liar N and exposure to ozone on foliar carbohydrate reserves of 20-yea r-old naturally regenerated saplings. The trees were maintained in nat ive soil in 360-1 containers for 5 years before the experiment. The ye ar before the experiment, trees were fertilized with N,P,K to provide a population of trees from N deficient to N sufficient. As foliar N de creased below 0.9%, length of current-year shoots and specific needle area of current-year needles declined. Foliar N concentration was corr elated with foliar sugar and starch concentrations, but relationships varied with time of year. Before bud break, foliar carbohydrates and N , in general, were positively correlated, and date of bud break was de layed in N-deficient trees. During active growth, foliar soluble sugar s and N were positively correlated, but starch concentrations were neg atively correlated with N. By late September, neither starch nor sugar concentration was correlated with N concentration. Ozone and foliar N concentrations did not interact to change foliar carbohydrate concent rations or shoot and needle growth in this relatively short-term study .