GROWTH AND PHYSIOLOGICAL-RESPONSE OF WATER-STRESSED YELLOW-POPLAR SEEDLINGS EXPOSED TO CHRONIC OZONE FUMIGATION AND ETHYLENEDIUREA

One-year-old containerized seedlings of yellow-poplar (Liriodendron tulipifera L.) were exposed to ethylenediurea (EDU), ozone (O-3) fumigation (0, 0.07, and 0.15 ppm), and drought (one or two 1-week drying cycles) from late April until early June 1990, at the Forestry Sciences Laboratory, Delaware, Ohio, USA, Measurements of net photosynthesis (P-n), dark respiration (Rd), stomatal conductance (G(s)), and transpiration (T-n) were made on seedlings from each treatment on 15 May and 31 May, Treatment effects on seedling growth were determined by measuring height increase, shoot and root biomass, and leaf area. Water stress significantly reduced P-n, G(s), and T-s (by more than 70%), whereas EDU and O-3 treatments had no appreciable effect on these parameters. There was no indication that ethylene evolution was influenced by any of the stress factors imposed in this study. There were no significant interactions between these stress factors and the physiological parameters measured. Growth measurements showed that height increase was reduced by 22% in water-stressed seedlings, whereas new shoot biomass, root biomass and leaf area declined by 10%, 20%, and 12%, respectively. New shoot biomass, root biomass, and leaf area were reduced by the EDU treatment. Root/shoot ratio was not significantly altered by the drought treatment employed. Overall, there were no significant effects of O-3 fumigation on growth. The interaction of water stress and O-3 fumigation at 0.07 ppm significantly reduced root biomass and the root/shoot ratio. The EDU and 0.15 ppm O-3 together reduced height growth more than either factor alone.