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

对于生活在水生环境光区的生物体来说，暴露于太阳紫外线辐射 (UVR) 是不可避免的事实。越来越明显的是，浮游动物、浮游植物、原生动物和浮游细菌在对紫外线照射的生理和行为反应中表现出分类特异性差异。尽管养分竞争被认为是构建浮游生物群落组成的关键因素，但自然条件下紫外线辐射对于浮游生物之间限制矿质养分的竞争强度的重要性尚不清楚。拟议的研究将有助于填补这一知识空白。我们将研究营养和 UVR 制度对天然浮游植物和浮游细菌的生长速率和磷竞争的主要影响和相互作用。提出了一个模型，并对一定范围的养分（有机碳和磷）比例和紫外线照射条件下养分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率的影响不同，紫外线将改变浮游植物和浮游细菌之间对磷的竞争的严重程度。将利用从密西西比州北部低海拔水库采集的样本进行实验来检验模型的预测。这项研究满足了两个需求。它将首次利用自然阳光通过实验评估紫外线辐射和营养状况的相互作用对不同程度营养限制下自养和异养浮游生物生长速率的影响。其次，它将提供有关紫外线辐射状况对美国南部水生生态系统中自养和细菌异养生产相对重要性的影响的知识，与高纬度地区相比，关于紫外线辐射的生态意义的研究很少。学生将参与该项目的各个方面，从规划到采样到数据分析到演示。由于臭氧消耗，预计温带地区的紫外线辐射将持续增加，紫外线辐射对浮游生物营养级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.