Detrital microbial community development and phosphorus dynamics in a stream ecosystem

Detrital microbial community development and phosphorus dynamics in a lotic system were investigated in non-recirculating laboratory streams containing leaf detritus. Temporal patterns of microbial colonization, as determined by scanning electron microscopy, indicate leaf species dependency and that bacteria were the first colonizers followed by fungi. An extensive glycocalyx layer developed.

Phosphorus incorporation rates of both the whole community and intracellular components were determined by time-course measurements of 33_P04 or 32_P04. The phosphorus incorporation rate for the maple community was 1.67 ng Ph^-1 cm^-2 and the rate for intracellular components ranged from 0.28 ng to 0.74 ng Ph^-1 cm^-2. The rates for the oak microbiota were 0.159 ng and 0.163 ng Ph^-1 cm^-2 and that for intracellular components ranged from 0.020 ng to 0.073 ng Ph^-1 cm^-2 and 0.022 ng to 0.069 ng Ph^-1 cm^-2 for the ungrazed and grazed microbiota, respectively.

Phosphorus turnover rates were determined by a sequential double-labeling procedure using 33_P04 and 32_P04, in which the microbiota were labeled with ³³p until in isotopic equilibrium, then ³²p was added. The turnover rate was determined by time-course measurements of the ratio ³²p to ³³p. The turnover rate for the maple community was 0.319% h^-1 and ranged from 0.379% h^-1 to 0.577% h^-1 for the intracellular components. The turnover rates for the ungrazed and grazed oak microbiota were 0.126% h^-1 and 0.131% h^-1, respectively, and ranged between 0.096% h^-1 to 0.194% h^-1 and 0.111% h^-1 to 0.245% h^-1 respectively for the intracellular components.

Snail grazing resulted in an increase in phosphorus metabolism per unit microbial biomass; however, per unit area of leaf surface no increase was observed. Grazing also caused a two-fold reduction in microbial biomass.

The results of this investigation indicate that microbiota associated with decomposing leaves slowly recycle phosphorus, are slowly growing, and have a low metabolic activity. The spiraling length is shortened by microbiota on a short-term basis; however, it may increase on a long-term basis due to hydrological transport of detritus downstream.