Is growth of filamentous cyanobacteria supported by phosphate uptake below the thermocline?

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• 作者：M. Nausch^a ; ^{monika.nausch@io-warnemuende.de} ; G. Nausch^b ; ^{guenther.nausch@io-warnemuende.de} ; V. Mohrholz^c ; ^{volker.mohrholz@io-warnemuende.de} ; H. Siegel^c ; ^{herbert.siegel@io-warnemuende.de} ; N. Wasmund^a ; ^{norbert.wasmund@io-warnemuende.de}
• 关键词：cyanobacteria ; diazotrophs ; phosphorus ; POC ; POP ratio ; DIP uptake ; Baltic Sea
• 刊名：Estuarine ; Coastal and Shelf Science
• 出版年：2012
• 期刊代码：79_02727714
• 类别：env
• 出版时间：1 March, 2012
• 卷：99
• 期：Complete
• 页码：50-60
• 文件大小：1500 K

摘要

In the Baltic Sea, excess phosphorus after the spring bloom or phosphorus input from deeper layers e.g. by upwelling are nutrient sources for the development of filamentous cyanobacteria. The objective of this study was to investigate the ability of filamentous cyanobacteria to accumulate phosphate in depths within or below the thermocline under stratified conditions in the water column. Inorganic nutrient concentrations, as well as phytoplankton composition, chlorophyll a, POC, PON and POP and the ratios between them of water samples and of isolated filamentous cyanobacteria were estimated in five horizons of the upper 30聽m surface layer together with phosphorus uptake and nitrogen fixation. During the investigation period, the water column was stratified with a surface temperature of 16聽掳C-18聽掳C in the eastern Gotland Basin. Cyanobacteria surface blooms occurred and constituted between 28 and 68%of the total phytoplankton biomass in the upper 5聽m surface layer. Deduced from POC:POP ratios of 264-977, cyanobacteria were phosphorus depleted here. The POC:POP ratios became lower with increasing depth. In depths below 15聽m, the cyanobacteria indicated phosphorus enrichment by POC:POP ratio declining down to 75 due to a forced gross uptake of 0.62聽nmol聽P聽渭g^鈭?聽Chla聽h^鈭?compared to an uptake rate of 0.13聽nmol聽P聽渭g^鈭?聽Chla聽h^鈭? measured in the surface layer. Thus, filamentous cyanobacteria can acquire phosphate in deeper layers which enables further growth when they reach the surface. However, they occurred in low abundances there. In 30聽m depth, cyanobacteria accounted for only 0.3-10%of their biomass in the surface layer. This contribution to bloom formation may therefore be of minor importance compared to other sources.