Evidence of microbial succession on decaying leaf litter in an arctic lake

Abstract

Microbial colonization and its relation to the decomposition of sedge (Carex) leaf litter were studied in the littoral area of Toolik Lake, Alaska. Colonization was assessed using scanning electron microscopy and by measuring the concentration of ATP associated with the litter. Litter lost approximately 20% of its dry weight and 60% of its phosphorus by leaching during the first 4 days of exposure to lake water. Microbial activity was responsible for any additional decomposition. Microorganisms were first observed on the litter surface on the 3rd day of incubation in the lake, when isolated bacterialike forms and microbial filament were present, but ATP was not yet detected. This initial appearance of microbes was followed by a dramatic rise in ATP concentration and a rapid proliferation of microbial forms, especially large filaments. Associated with this rapid colonization was a steep decline in nitrogen content, a twofold increase in protein content, and the appearance of microbially mediated weight loss of the litter. By day 13, microbial colonization declined by 50% and remained stabilized at this lower level for the duration of the study. This decline coincided with the demise of the large filamentous forms, a decrease in the protein content of the litter, and slower but continued decrease in the nitrogen content of the litter. As time progressed, the microbial community became increasingly characterized first by the presence of bacterialike forms enmeshed in slime and later by large numbers of penna*** diatoms. These findings show that decomposition is dependent on the development and succession of the microbial community on the litter.