Underway Mapping of Alkaline Phosphatase Activity in the Mississippi River Plume: Real-Time Evidence for Phosphorus Limitation

水环境中微生物胞外酶活性是聚合物水解的重要因素，也是微生物碳、氮、磷营养状况的指标。尤其是碱性磷酸酶，是磷限制的一个很好的指标。然而，像大多数其他生化和分子测量一样，胞外酶活性，包括碱性磷酸酶，一直局限于谨慎的水样。我们开发了一种使用高灵敏度荧光底物连续测量碱性磷酸酶和其他微生物酶活性的方法。该方法已成功地用于绘制密西西比河羽流和路易斯安那州陆架有限区域的表面碱性磷酸酶活性图，该区域可能是磷限制最强烈的区域。这项拟议的研究将使用改进的自动化酶测量系统，对密西西比河羽流和路易斯安那州海岸沿线的地表水碱性磷酸酶活性进行广泛的季节性测绘。该系统将与船提供的温度、盐度、活体荧光和其他参数的连续在航测量相结合。这项工作将与Quay Dortch和David Nelson之前资助的关于该地区氮、磷和二氧化硅限制的综合工艺研究一起进行。季节碱性磷酸酶图谱将提供有关磷限制的空间和时间范围的重要信息，这将有助于多尔奇和纳尔逊进行详细的营养强化实验的站点选择。这些养分富集化实验反过来将提供有关群落对养分富集化的反应的详细信息，这将有助于解释绘图数据。此外，还将对营养强化实验的样本进行碱性磷酸酶测量，以帮助解释它们的生理状态。

Microbial ectoenzyme activities in aquatic environments are important agents of polymer hydrolysis and indicators of the state of microbial carbon, nitrogen, or phosphorus nutrition. Alkaline phosphatase, in particular, is a good indicator of phosphorus limitation. However, like most other biochemical and molecular measurements, ectoenzyme activities, including alkaline phosphatase, have been limited to discreet water samples. We have developed a continuous underway method for measuring alkaline phosphatase and other microbial enzyme activities using high-sensitivity fluorescent substrates. This method has been successfully employed to map surface alkaline phosphatase activity in a limited area of the Mississippi River plume and the Louisiana shelf, the area where phosphorus limitation is likely to be most intense. This proposed study will use an improved automated enzyme measurement system for extensive seasonal mapping of surface water alkaline phosphatase activity in the Mississippi plume and along the Louisiana coast. This system will be coupled with continuous underway measurements of temperature, salinity, in vivo fluorescence and other parameters provided by the ship. This work will be conducted in conjunction with a previously-funded comprehensive process study of nitrogen, phosphorus, and silica limitation in this area to be conducted by Quay Dortch and David Nelson. The seasonal alkaline phosphatase mapping will provide importantinformation on the spatial and temporal extent of phosphorus limitation, which will aid in the selection of stations for detailed nutrient enrichment experiments by Dortch and Nelson. These nutrient enrichment experiments, in turn, will supply detailed information on the response of the community to nutrient enrichment, which will help in the interpretation of the mapping data. Additional alkaline phosphatase measurements will be made on samples from the nutrient enrichment experiments to help in the interpretation of their physiological status.