Earlier discussions emphasized that dead organic matter, called detritus, exists as a spectrum from dissolved organic compounds, organic colloids, and larger particles of organic matter. Dissolved organic matter is in much greater abundance, by about five to ten times, than is particulate organic matter. All microflora must degrade particulate organic matter enzymati-cally to the dissolved form prior to assimilation for further metabolic breakdown and eventual mineralization to inorganic solutes and gases.
The rates of growth by bacteria and their productivity are known poorly from aquatic ecosystems. Much of this lack of progress resulted from the slow application of laboratory methodology to heterogeneous natural communities of bacteria. Often methods were developed for isolated strains at high laboratory concentrations. A number of methods have been developed recently that permit examination of growth and productivity of in situ communities of bacteria. These methods are evolving as more is learned about metabolic constraints and variations.
Natural variance is high in microbial communities, and many organisms are metabolically inactive or dormant. The methods used to examine bacteria are labor intensive. We describe methods here in considerable detail because they require rigorous application in order to obtain meaningful results. Conversion of rates of biomass change or genetic replication to actual rates of carbon flux in bacterial secondary productivity is difficult and is undergoing intensive study by many researchers. A spectrum of conversion factors is given for different environmental conditions in order to indicate the range of probable in situ values.
We stress the importance of these evaluations of in situ metabolism and growth rates of bacteria. Much of the understanding about biogeo-chemical cycling in aquatic ecosystem has been limited severely by poor or inadequate techniques for evaluation of bacterial metabolism and its limitations by environmental parameters. The methods presented here are not perfect, and they are laborious. Certainly they will improve with time. However, these methods offer means to examine in situ rates of bacterial growth and productivity and, importantly, means to evaluate in situ effects of experimental manipulations of environmental conditions.
KeywordsAcridine Orange Thymidine Incorporation Tritiated Thymidine Lewis Publisher Thymidine Uptake
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