FACTORS LIMITING MICROBIAL ACTIVITIES IN SOIL: III. SUPPLEMENTARY SUBSTRATE ADDITIONS

Abstract

Studies were conducted to examine further the circumstances prevailing during the phase of rapid decline in the respiration rate of soil after the addition of a soluble carbon substrate, and to investigate the potential metabolic activity of the microbial population at different stages in its sequential development. When the supply of required inorganic nutrients was adequate, the rapid decline in the rate of respiration following attainment of the respiratory peak resulted primarily from depletion of available carbon substrates, even though by this time only 30 to 50% of the carbon in the substrate (glucose) added had been recovered as CO2. Supplementary additions of the same substrate, regardless of the concentration and time of addition, however, did not elicit secondary peaks comparable in height to the primary peaks, nor was the recovery as CO2 from the supplements as high as from the initial substrate addition. This attenuation of the metabolic activity was attributed to limiting factors introduced by the initial growth of a large and active microbial population which restricted the development of sequential populations. The nature of these limiting factors and their implication in maintaining the ecological balance of microorganisms in soil are discussed.