The Effect of Irrigation Frequency on Growth and Physiology of Native Landscape Shrub Species
Type of DegreeThesis
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Studies were conducted utilizing the Horhizotron™ to evaluate horizontal root growth of Morella cerifera (L.) Small (syn. Myrica cerifera) (wax myrtle) and Illicium floridanum Ellis (Florida anise tree) when portions of the root system were exposed to different levels of soil moisture. Four different irrigation frequencies were randomly assigned among the four quadrants in each Horhizotron and consisted of: watered daily, unwatered, and watered once 10% or 15% moisture by volume was reached. In the first experiment, M. cerifera and I. floridanum HRL decreased with decreasing irrigation frequency as did root dry weights. In the second experiment no difference in HRL or root dry weights was seen among treatments for M. cerifera however, HRL and root dry weight decreased with decreasing irrigation frequency for I. floridanum. This experiment indicates that roots of both species can persist under a range of irrigation frequencies as long as some portion of the root ball receives some water. Additional studies were conducted to evaluate the effect of irrigation frequency on horizontal rowth and physiology of K. latifolia. In the first experiment, one of three different irrigation frequencies was assigned to all four quadrants of a Horhizotron and consisted of watered-daily or rewatered once substrate percent moisture reached 15% or 10% by volume. Stem water potential and net photosynthesis were measured for the control or once each substrate reached the desired minimum percent moisture. In a second experiment, four different irrigation frequencies randomly assigned among the four quadrants in each Horhizotron and consisted of: watered-daily, unwatered, and rewatered once substrate percent moisture reached 15% or 10% moisture by volume. During the first experiment, HRL was highest in the watered-daily substrate, however, HRL was highest in the unwatered substrate during the second experiment. There were no differences in RDW in either experiment. SDW and GI were highest for plants in the watered-daily substrate in the first experiment. Stem water potential increased with decreasing soil moisture, and net photosynthesis decreased with decreasing soil moisture. These experiments indicate that soil water deficit affects root growth of K. latifolia differently depending on if (A) the entire root ball is experiencing soil water deficit, or (B) if only part of the root ball is experiencing soil water deficit. Additionally, stem water potential and net photosynthesis provided good information about the response of K. latifolia to different irrigation frequencies.