ESTIMATION OF THE GROWTH-RATES OF EPIPHYTIC BACTERIA AND LEMNA-MINOR IN A RIVER

SUMMARY. Growth of Lemna minor fronds in the River Frome during summer was found to be logarithmic with time and the growth rate (log10) was 0.066 day−1. This is equivalent to a doubling time of 4.5 days. The life expectancy of the fronds was 34 days. The net change in the density of bacteria epiphytic on the lower surface of Lemna fronds in the R. Frome was monitored using a direct microscopic technique. The observed increase in bacterial numbers has been partitioned into the components of attachment and growth, assuming that attachment occurred at a constant rate and that the bacterial population grew logarithmically. The line which fitted the data best gave an attachment rate of 5.7 × 105 bacteria cm−2 day−1 and a growth rate (log10) for the bacteria of 0.044 day−1 which is equivalent to a doubling time of 164 h. Estimates of the rate of detachment of bacteria from Lemna plants were obtained from a laboratory experiment which assumed negligible growth of bacteria in 1 h. The number of bacteria which detached per hour and the sizes of the bacterial populations on the plants before and after detachment were estimated using a plating technique. Different detachment rates were monitored. The detachment rate (analogous to growth rate) which is judged to be most similar to an in situ value was 0.0031 h−1 (0.074 day−1). This rate added to the specific growth rate given above resulted in a corrected growth rate of 0.118 day−1 equivalent to a doubling time of 61 h. Copyright © 1979, Wiley Blackwell. All rights reserved