Dynamics of bacterial populations in relation to carbon availability in a residue-amended soil

Bacterial response to alteration in C availability is important in understanding the microbial community structure and microbial interactions in soil ecosystems. Population dynamics of oligotrophic and copiotrophic bacteria in relation to soil C availability were examined and relationships between bacterial populations and water-extractable C, buffer-extractable C, mineralizable C or microbial biomass C were investigated. Both copiotrophs and oligotrophs were signi®cantly stimulated by newly added C in the form of cover crop debris, but copiotrophs rapidly peaked at the very early stage of cover crop decomposition while peak populations of oligotrophs occurred at a later stage when available C decreased. Despite signi®cant correlations between mineralizable C and water soluble C or buffer soluble C, dynamics of both copiotrophic and oligotrophic bacteria was best related to mineralizable C pool. Copiotrophs were logarithmically correlated to mineralizable C (p < 0.0001), while oligotrophs were quadratically related to mineralizable C (p < 0.0001), which is, to our knowledge, the ®rst report showing that high C availability may have inhibited oligotrophs in natural soils. Oligotrophs were not signi®cantly correlated to microbial biomass C, suggesting that oligotrophs only contributed a minor part to the soil microbial biomass pool. # 1999 Elsevier Science B.V. All rights reserved.