Arbuscular mycorrhizal fungi (AMF) form mycorrhizae, a common, well-studied symbiotic relationship. Controls on the magnitude and direction of plant mycorrhizal growth response (MGR) remain obscured. Specifically, the influence of light availability in the MGR of an invasive forb, spotted knapweed Centaurea stoebe, has not been studied. Greenhouse studies exploring the growth response of knapweed to arbuscular mycorrhizae (AM) often fail to report light intensity levels, which could impact the quality of their data. I conducted a greenhouse experiment studying the MGR in spotted knapweed under shaded and unshaded conditions, designed to approximate light availability in ambient greenhouse and full-sun conditions, respectively. I found that AMF decreased biomass of plants in unshaded conditions, but had no effect under shaded conditions. I suggest possible explanations for the observed negative MGR and conclude that light availability affects the MGR of spotted knapweed.
O'Kelley, Regina, "Reduced Light Availability Diminishes Mycorrhizal Growth Response of Invasive Forb" (2017). WWU Honors Program Senior Projects. 63.