Date of Award

5-2004

Document Type

Thesis

Department

Biology

First Advisor

Paul W. Bartholomew

Second Advisor

Robert D. Williams

Third Advisor

Sonya J. Williams

Abstract

The rate of leaf appearance and onset of growth in cool season grasses may be influenced by soil moisture potential and exposure to below freezing temperatures. Levels of moisture potential and days exposed to freezing temperatures, which will restrict leaf appearance, are not well defined. The first part of this study was to determine the effects of different moisture potentials on the leaf appearance rates in two cool season grasses. Italian ryegrass (IRG) and tall wheat grass (TWG) were grown hydroponically at 4 moisture potentials in seed pouches in an incubator under a photoperiod of 13 hours light and 11 hours dark and at day/night temperatures of 17.5°C and 12.5°C. The mean leaf appearance rate, regardless of treatment, in IRG was 20% greater than TWG. As moisture potential increased the leaf appearance rate decreased in both species. On average, when the moisture potential was -0.7 MPa, it caused a decrease in the leaf appearance rate of 68% and 44% in IRG and TWG, respectively, as compared to the control. The second part of this study was to determine the effects of below freezing temperature treatments at three levels of moisture stress on the leaf appearance in two cool season grasses. Italian ryegrass (IRG) and tall fescue (TF) were grown in soil at three different volumetric water contents (10%, 20% and 30%), in addition to a treatment of cold at -5°C (overnight) for 0, 2 or 4 occasions. As cold treatment days and moisture stress increased, the leaf appearance rate decreased in both cool season grasses. When subjected to a 30% moisture stress and having no exposure to below freezing temperatures, the phyllochron of IRG and TF was 80.4 and 90.3 (growing day degrees) respectively. With 4 exposures to -5°C, the phyllochron was increased to 99.7 and 123.4 for IRG and TF, respectively.

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