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

暴露于太阳紫外线辐射(UVR)是生活在水生环境光区的生物的一种现实。越来越明显的是，浮游动物、浮游植物、原生动物和浮游细菌在对紫外线照射的生理和行为反应上表现出特定分类群的差异。尽管营养物质的竞争被认为是构成浮游生物群落组成的关键因素，但在自然条件下，对于浮游生物之间竞争限制矿物质营养的激烈程度，人们对紫外线辐射的重要性一无所知。这项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制度对自然浮游植物和浮游细菌的生长速度和对磷的竞争的主要和交互影响。建立了一个模型，并对营养物(有机碳和磷)比例和UVR暴露条件下营养物竞争的严重程度进行了预测。我们预测，由于对浮游细菌和浮游植物生长速度的不同影响，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，将进行实验以验证模型预测。这项研究满足了两个需求。这将是第一次通过利用自然阳光的实验来评估在不同程度的营养限制下UVR和营养制度对自养和异养浮游生物生长速度的交互作用。第二，它将提供关于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，那里与高纬度相比，对UVR的生态意义的研究很少。学生将参与该项目的所有方面，从规划到采样，到数据分析再到演示。由于预计由于臭氧消耗而导致的温带地区紫外线辐射持续增加，紫外线辐射对浮游生物营养水平关系的影响构成了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.