Determination of bacterial and fungal fumigation κc factors across a soil moisture gradient

Six samples of agricultural soil were maintained at five separate soil moisture contents (15, 25, 35, 45 or 55%) for 6 h or 3, 10 or 30 days. These samples were then amended with 14C-labelled fungal or bacterial tissue, and the k c values determined following chloroform fumigation. Soil moisture effects explained 12.5% of the variation in the data set for fungal k c factors, and 9.5% in the bacterial data set. The 15% moisture treatment always had lower k c values than for at least some of the other moisture contents, in both the fungal and bacterial data sets but the differences were usually small. The 25, 35, 45 and 55% treatments did not usually differ from each other. Duration of incubation had a much stronger effect, explaining 51.6 and 35.8% of variation in the fungal and bacterial data sets, with prolonged incubation depressing k c values. The significance of blocking effects in each case indicated that the six samples (blocking units) had different k c values. Analysis of k c values, determined for the entire microbial biomass using a bacterial:fungal ratio of 25:75, showed essentially similar responses to the treatment effects tested for. Values of k c, determined using a different bacterial:fungal ratio determined for each subsample, were almost identical to those using a bacterial: fungal ratio of 25:75.