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At the Root of It: Investigating the Effects of Noise Pollution on Directional Root Growth Shayna Engdahl, Molly Williams, Dr. William Quinn Department of Biological Sciences, St. Edward’s University, Austin, Texas
Abstract: It has long been understood that roots exhibit directional growth in response to stimuli such as moisture, gravity, and touch. However, a recent study found that in the absence of a moisture gradient or any other known stimuli, Pisum sativum roots use vibrations to locate water sources. This has led to questions regarding any correlations between noise pollution and the effectiveness of plant roots to locate water sources using solely vibrations. Previous research has demonstrated the devastating effects of noise pollution on aquatic life, humans, and other organisms but has yet to investigate the effects on plant life. In this study, we tested the impact of competing noise on the roots’ effectiveness to acoustically locate a water source. Our findings suggest that when competing noise is present, the accuracy is diminished, therefore potentially illuminating consequences of noise pollution on plant life. Introduction: It is widely believed that plants invaded land 460 million years ago1, succeeding mainly through effective water acquisition and conservation. Natural selection has produced a number of easily recognized mechanisms for these adaptations 2 including the CAM photosynthetic pathway3, the abundance of thick cuticles and reduction of leaf size in dry environments4, and development of leaf hairs5, among others. Relatively little is known about how natural selection has selected for plants whose roots are better able to grow toward water. Recently, Gagliano et al.6 have indicated that the radicle of Pisum sativum seedlings appears to respond to acoustic cues that come from running water, directing root growth toward the source. That is, the radicles may “hear” and respond to the vibration of running water, even in the absence of a moisture gradient. Given the potential importance of this acoustic cue, the increase in anthropogenic background noise associated with urbanization may affect this suggested ability to “hear” water. Therefore, we intend to provide information about the potential for human noise pollution to impact this phenomenon. The agronomic and economic consequences may be substantial. Specifically, this study is intended to clarify this relationship by testing whether the ability to locate a water source solely using acoustic cues is diminished when competing noise is present. It is hypothesized that if plants locate water sources using acoustic vibrations, then when a P. sativum seedling is exposed to co-occurring sounds, the difference in the tendency of roots to grow in the direction of the water source will be offset. It is believed that the human-made sound will create a “masking” effect, essentially drowning out the vibrations of the running water. Methods: Experiment 1: First, we attempted to validate the results reported by Gagliano et al. that pea seedling radicle directional growth is affected by the presence of running water. In this set of experiments, no competing noise was included. P. sativum seedlings were exposed solely to the vibrations of running water and the sides of the manipulation and placement were assigned randomly. Seeds were germinated using the rag-doll technique and once the radicle was 5 mm or