The Ecological and Physiological Significance of the Growth of Heterotrophic Microorganisms with Mixtures of Substrates

Abstract

It has been estimated that globally some 500 × 1012 kg of carbon dioxide are assimilated into biomass by autotrophic organisms annually. More than 99% of this assimilated carbon is remineralized, keeping the global biogeochemical carbon cycle roughly in balance (Hedges, 1992). In both terrestrial and aquatic ecosystems the majority of this primary biomass is not consumed directly by herbivorous animals, but decays to detritus and serves as a nutritional basis for the growth of consumers (for an extensive discussion, see Fenchel and Jørgensen, 1977). There is now substantial evidence suggesting that a large part of the energy and nutrients contained in this primary biomass is processed via the microbial detritus food chain, and this mineralizing ability makes heterotrophic microorganisms an important link in the global carbon cycle (Fenchel and Jørgensen, 1977; Paul and Voroney, 1980; Wetzel, 1984; Cole et al., 1988; Mann, 1988). In addition, their ability to mineralize man-made xenobiotic organic chemicals has become increasingly important. This is illustrated by the fact that in industrialized countries the flux of synthetically produced organic material, much of which is ending up in the environment, has increased within the past two centuries to some 40 g C m−2 year−1. This figure is equivalent to approximately 15% of the net primary biomass production in these regions (Egli, 1992).