Interaction Effects of Solar Ultraviolet Radiation and the Nutrient Environment on the Dynamics of Growth of Freshwater Bacteria and Phytoplankton

太阳紫外线辐射（UVR）是生活在水生环境光区的生物的生活事实。越来越明显的是，浮游动物、浮游植物、原生动物和浮游细菌对紫外线辐射的生理和行为反应表现出不同分类群的差异。尽管对营养物质的竞争被认为是构成浮游生物群落组成的一个关键因素，但人们对自然条件下浮游生物之间争夺限制性矿物质营养物质的竞争强度的重要性一无所知。拟议的研究将有助于填补这一知识空白。我们将研究营养物和紫外线照射对天然浮游植物和浮游细菌的生长速率和对磷的竞争的主要和相互作用。提出了一个模型，并对不同营养物质（有机碳和磷）比例和紫外线照射条件下的养分竞争程度进行了预测。我们预测，由于UVR对浮游细菌和浮游植物生长速率的不同影响，UVR将改变浮游植物和浮游细菌对磷的竞争程度。使用从密西西比州北部一个低海拔水库收集的样本，将进行实验来测试模型的预测。这项研究满足了两个需求。这将是第一个利用自然光进行实验，评估在不同程度的营养限制下，紫外线辐射和营养制度对自养和异养浮游生物生长速率的相互作用。其次，它将提供有关UVR制度对美国南部水生生态系统中自养和细菌异养生产的相对重要性的影响的知识，与高纬度地区相比，那里对UVR的生态意义的研究很少。学生将参与项目的各个方面，从计划到抽样，从数据分析到演示。由于臭氧损耗，预计温带地区UVR将持续增加，因此UVR对浮游生物营养层关系的影响是一个及时而重要的问题。

Exposure to solar ultraviolet radiation (UVR) is a fact of life for organisms living inthe photic zone of aquatic environments. It is increasingly evident that zooplankton,phytoplankton, protozoa, and bacterioplankton exhibit taxon-specific differences inphysiological and behavioral responses to UVR exposure. Although competition fornutrients is recognized as a critical factor in structuring plankton communitycomposition, nothing is known of the significance of UVR under natural conditions for theintensity of competition among plankton for limiting mineral nutrients. The proposedresearch will help to fill this gap in knowledge. We will examine the main andinteraction effects of the nutrient and UVR regime on the growth rates and competition forphosphorus of naturally occurring phytoplankton and bacterioplankton. A model ispresented and predictions made regarding the severity of nutrient competition under arange in conditions of nutrient (organic carbon and phosphorus) ratios and UVR exposure.We predict that, because of differential effects on bacterioplankton and phytoplanktongrowth rates, UVR will modify the severity of competition between phytoplankton andbacterioplankton for phosphorus. Using samples collected from a low-altitude reservoir innorth Mississippi, experiments will be conducted to test the model predictions. Thisstudy fulfills two needs. It will be the first to evaluate by experimentation usingnatural sunlight the interaction effects of UVR and the nutrient regime on growth rates ofautotrophic and heterotrophic plankton under various degrees of nutrient limitation.Second, it will provide knowledge of the influence of the UVR regime on the relativeimportance of autotrophic and bacterial heterotrophic production in a southern U.S.aquatic ecosystem, where, compared to higher latitudes, there has been very littleresearch on the ecological significance of UVR. Students will be involved in all aspectsof the project, from planning to sampling to data analysis to presentation. Withanticipated continued increases of UVR in temperate regions due to ozone depletion, theeffect of UVR on plankton trophic-level relationships constitutes a timely and importantproblem.