【沿海水体富营养化】Mirko Lunau Maren Voss Matthew Erickson Claudia Dziallas Karen Casciotti Hugh Ducklow. Excess nitrate loads to coastal waters reduces nitrate removal efficiency: mechanism and implications for coastal eutrophication. Environmental Microbiology
Abstract
Terrestrial ecosystems are becoming increasingly nitrogen-saturated due to anthropogenic activities such as agricultural loading with artificial fertilizer. Thus more and more reactive nitrogen is entering streams and rivers primarily as nitrate where it is eventually transported towards the coastal zone. The assimilation of nitrate by coastal phytoplankton and its conversion into organic matter is an important feature of the aquatic nitrogen cycle. Dissolved reactive nitrogen is converted into a particulate form which eventually undergoes nitrogen removal via microbial denitrification. High and unbalanced nitrate loads to the coastal zone may alter planktonic nitrate assimilation efficiency due to the narrow stochiometric requirements for nutrients typically shown by these organisms. This implies a cascade of changes for the cycling of other elements such as carbon with unknown consequences at the ecosystem level. Here we report that the nitrate removal efficiency (NRE) of a natural phytoplankton community decreased under high unbalanced nitrate loads due to the enhanced recycling of organic nitrogen and subsequent production and microbial transformation of excess ammonium. NRE was inversely correlated with the amount of nitrate present and mechanistically controlled by dissolved organic nitrogen (DON) and organic carbon (Corg) availability. These findings have important implications for the management of nutrient runoff to coastal zones.
【暴露在长期环境变化条件下的细菌群落生物地理学】Ramiro Logares Eva S Lindström Silke Langenheder Jürg B Logue Harriet Paterson Johanna Laybourn-Parry Karin Rengefors Lars Tranvik and Stefan Bertilsson. Biogeography of bacterial communities exposed to progressive long-term environmental change. The ISME Journal (2013) 7 937–948
Abstract
The response of microbial communities to long-term environmental change is poorly understood. Here we study bacterioplankton communities in a unique system of coastal Antarctic lakes that were exposed to progressive long-term environmental change using 454 pyrosequencing of the 16S rDNA gene (V3–V4 regions). At the time of formation most of the studied lakes harbored marine-coastal microbial communities as they were connected to the sea. During the past 20 000 years most lakes isolated from the sea and subsequently they experienced a gradual but strong salinity change that eventually developed into a gradient ranging from freshwater (salinity 0) to hypersaline (salinity 100). Our results indicated that present bacterioplankton community composition was strongly correlated with salinity and weakly correlated with geographical distance between lakes. A few abundant taxa were shared between some lakes and coastal mari