IN SITU GROWTH RATE OF MICROCYSTIS IN A HYPERTROPHIC LAKE: RNA/DNA RATIO AS AN INDICATOR

摘要

The DNA content was employed as an indicator of algae biomass to improve the cellular RNA content method to estimate the in situ growth rate of Microcystis in a hypertrophic lake (Lake Taihu, China). Microcystis aerugi-nosa was cultured in BG-11 and M-11 mediums, respectively, and a significant relationship between cell density and DNA concentration of Microcystis was found. Then a significant logarithmic relationship between Microcystis growth rate and RNA/DNA ratio was established to measure growth rate of Microcystis by analysis of RNA and DNA content. The growth rates calculated by RNA/DNA method were in good agreement with that calculated by the changes of cell density in the whole water column respected with time. The RNA/DNA method was applied in Lake Taihu in summer (1st July) and autumn (1st October), respectively. In summer, the maximum growth rate was 0.361 day~(-1) and others were from 0.04 to 0.34 day~(-1) with an average value of 0.12, four values were below zero; In autumn, the maximum growth rate was 0.111 day~(-1) and most values were below zero. Our results also demonstrated that the growth rate of Microcystis was higher inshore than offshore.