Effects of Aeration, Water Supply, and Nitrogen Source on Growth and Development of Tupelo Gum and Bald Cypress

Seedlings of tupelo gum (Nyssa aquatica L.) and bald cypress (Taxodium distichum L. Rich.) were cultured in saturated—aerated, saturated, and unsaturated soil. Experiments were designed to (1) measure and evaluate the relative reaction of tupelo and cypress to various soil—moisture conditions (2) determine the effects of aeration and water availability on plant moisture stress and growth; and (3) compare effects of two forms of nitrogen fertilizer (urea and nitrate) on growth. On the basis of height and dry weight, both tupelo and cypress grew best in saturated—aerated soil. Growth was better in saturated soil than in unsaturated soil, but only when water in the unsaturated soil decreased substantially below field capacity before rewatering. Plant moisture stress was determined by a pressure—bomb technique. For tupelo, average daily maximum tensions were 7.2 and 7.0 atm (atm = 1.013 bar) with saturated and unsaturated soil, respectively; for cypress, comparative tensions were 10.9 and 8. 5 atm. When soil moisture decreased from field capacity to the wilting point, the daily maximum tension in plants increased from 7.0 to 12.8 and from 8.5 to 17.6 atm in tupelo and cypress, respectively. Growth of plants was related to the cumulative effect of their internal moisture stress. When tupelo plants were subjected to 595 atm—days (daily maximum tension X number of days with that tension), height growth was 37% and dry weight 40% less than plants subjected to 490 atm—days. Fertilization with urea produced more growth than fertilization with nitrate.