Andersen, Christian P. and C. S. Scagel. 1997. Nutrient availability alters below-ground respiration of ozone-exposed Ponderosa pine. Tree Physiology 17:377-387.
Exposure to ozone (O3) and changes in soil fertility influence both the metabolism of plant roots and their interaction with rhizosphere organisms. Because one indication of altered root metabolism is a change in belowground respiratory activity, we used specially designed measurement chambers to assess the effects of O3 and nutrient availability on belowground respiratory activity of potted three-year-old ponderosa pine (Pinus ponderosa Dougl. ex Laws.). Seedlings were exposed to a factorial combination of three O3 treatments and three fertilization treatments in open-top O3 exposure chambers. Ozone exposure decreased and high nutrient supply increased total plant dry weight, but root/shoot ratios were not affected. In general, exposure to O3 increased rates of belowground O2 uptake and CO2 release and the respiratory quotient (RQ, CO2/O2), although seasonal differences were detected. In October, following the second season of O3 exposure, rates of belowground O2 uptake and CO2 release and RQ were increased in trees in the high-O3 exposure treatment by 22, 73 and 32%, respectively, over values in control trees in charcoal-filtered air. Increasing nutrient supply resulted in decreasing rates of belowground O2 uptake and CO2 release but it had little effect on RQ. In the high-nutrient supply treatment, rates of belowground O2 uptake and CO2 release were decreased by 38 and 39%, respectively, compared with rates in the low-nutrient supply treatment. At the end of the second growing season, the high-nutrient supply treatment had decreased lateral root total nonstructural carbohydrates by 22% compared with the low nutrient supply treatment.