Huss A A, Wehr J D
Louis Calder Center--Biological Field Station and Department of Biological Sciences, Fordham University, Armonk, NY 10504, USA.
Microb Ecol. 2004 May;47(4):305-15. doi: 10.1007/s00248-003-1034-7. Epub 2004 Mar 25.
Phytoplankton and allochthonous matter are important sources of dissolved organic carbon (DOC) for planktonic bacteria in aquatic ecosystems. But in small temperate lakes, aquatic macrophytes may also be an important source of DOC, as well as a source or sink for inorganic nutrients. We conducted micro- and mesocosm studies to investigate the possible effects of an actively growing macrophyte, Vallisneria americana, on bacterial growth and water chemistry in mesotrophic Calder Lake. A first microcosm (1 L) study conducted under high ambient NH4+ levels (NH4+ > or = 10 microM) demonstrated that macrophytes had a positive effect on bacterial densities through release of DOC and P. A second microcosm experiment, conducted under NH4+-depleted conditions (NH4+ < 10 microM), examined inter- active effects of macrophytes and their sediments on bacterial growth and water chemistry. Non-rooted macrophytes had negative effects on bacterial numbers, while rooted macrophytes had no significant effects, despite significant increases in DOC and P. A 70-L mesocosm experiment manipulated macrophytes, as well as N and P supply under surplus NH4-+conditions (NH4+ > or = 10 gmicro), and measured effects on bacterial growth, Chl a concentrations, and water chemistry. Bacterial growth and Chl a concentrations declined with macrophyte additions, while bacterial densities increased with P addition (with or without N). Results suggest that the submersed macrophyte Vallisneria exerts a strong but indirect effect on bacteria by modifying nutrient conditions and/or suppressing phytoplankton. Effects of living macrophytes differed with ambient nutrient conditions: under NH4+-surplus conditions, submersed macrophytes stimulated bacterioplankton through release of DOC or P, but in NH4-+depleted conditions, the influence of Vallisneria was negative or neutral. Effects of living macrophytes on planktonic bacteria were apparently mediated by the macrophytes use and/or release of nutrients, as well as through possible effects on phytoplankton production.
浮游植物和外源物质是水生生态系统中浮游细菌溶解有机碳（DOC）的重要来源。但在小型温带湖泊中，水生大型植物也可能是DOC的重要来源，以及无机养分的一个来源或汇。我们进行了微型和中型生态系统研究，以调查一种正在生长的大型植物——美洲苦草，对中营养的考尔德湖细菌生长和水化学的可能影响。在高环境铵（NH₄⁺）水平（NH₄⁺≥10微摩尔）下进行的第一个微型生态系统（1升）研究表明，大型植物通过释放DOC和磷对细菌密度有积极影响。在铵耗尽条件（NH₄⁺＜10微摩尔）下进行的第二个微型生态系统实验，研究了大型植物及其沉积物对细菌生长和水化学的交互作用。无根大型植物对细菌数量有负面影响，而有根大型植物则没有显著影响，尽管DOC和磷显著增加。一个70升的中型生态系统实验在铵过剩条件（NH₄⁺≥10微克）下控制了大型植物以及氮和磷的供应，并测量了对细菌生长、叶绿素a浓度和水化学的影响。添加大型植物后细菌生长和叶绿素a浓度下降，而添加磷（无论有无氮）后细菌密度增加。结果表明，沉水大型植物美洲苦草通过改变营养条件和/或抑制浮游植物对细菌产生强烈但间接的影响。活的大型植物的影响因环境营养条件而异：在铵过剩条件下，沉水大型植物通过释放DOC或磷刺激浮游细菌，但在铵耗尽条件下，苦草的影响是负面的或中性的。活的大型植物对浮游细菌的影响显然是由大型植物对养分的利用和/或释放介导的，以及可能对浮游植物生产的影响。
