| Individual plants benefit from the mycorrhizal condition primarily by improved nutrient uptake, especially phosphorus (P), resulting in enhanced plant survival and growth in resource-limited conditions. On a broader scale, mycorrhizas have the potential to mediate plant competition and subsequently may be important at the community level. In the southeastern United States, slash pine (Pinus elliottii Engelm. var. elliottii) is grown in plantations, where it competes for nutrients with grasses and other herbaceous vegetation.; The goal of my research was to assess mycorrhizal contribution to intra- and interspecific plant competition for P in the greenhouse between pine and Panicum chamaelonche Trin., a dominant grass species at a local plantation site. The grass was inoculated or not with the arbuscular mycorrhizal (AM) fungus, Glomus sp. (INVAM FL329, formerly INVAM FL906), and pine was inoculated or not with the ectomycorrhizal (EM) fungus, Pisolithus tinctorius (isolate S106). The effect of P (0.32, 3.23 or 32.26 {dollar}mu{dollar}M) on competition also was analyzed in the greenhouse since resource abundance can affect the outcome of competition, and inorganic P is limiting in pine plantations. Inoculated grasses were not colonized at the end of the experiment and were excluded from data analyses. Based on shoot-P content, inoculated pine was more competitive than noninoculated pine when competing with grass. Grass shoot-P content was reduced only when competing with pine, irrespective of the pine inoculation treatment. This response occurred only at the 32.26 {dollar}mu{dollar}M P level indicating a resource-dependent response.; I evaluated the effects of benomyl over time in the field and at 0, 20, 60 and 150 kg benomyl ha{dollar}sp{lcub}-1{rcub}{dollar} equivalent in the greenhouse. My objective was to determine if benomyl would be suitable for controlling AM but not EM fungi as part of a larger competition experiment involving pine and weeds. No effect was observed on pine in the greenhouse. Colonized root length of benomyl-treated Zea mays L. plants in the greenhouse remained static and the response was not dose-dependent. In contrast, colonization in the control plants increased over time. Minimal reduction of grass colonization was observed in the field where limitations to effective control were ground cover, timing in relation to mycorrhizal development and benomyl application as a spray instead of as a soil drench. |
