Evaluating the 'triggering response' in soils, using C-13-glucose, and effects on dynamics of microbial biomass

摘要

Very small inputs of labile substrates can cause several more times CO2 -C to be rapidly evolved from soil than was contained in the added substrates. This effect, termed the triggering response, does not currently have a conclusive mechanistic explanation. In this work C-13-labeled glucose was added (10 mu g glucose C g(-1)-soil) to two Chinese soils, one from a mulberry plantation and another from a grassland soil. An immediate and significant increase in CO2 -C evolution occurred from 0 to 72 h after glucose addition in both soils and, after 7 days of incubation. It was equivalent to 149.2% and 195.4% respectively of the C added as glucose. The dynamics of CO2-C, glucose mineralization, ATP and microbial biomass C (biomass C) were monitored in the amended and nonamended control soils after glucose addition (0-3, 3-5, 5-8, 8-24, 24-72 and 72-168 h). The most rapid increase in cumulative triggered CO2-C, glucose mineralization and ATP concentrations occurred within 3-5 h and the largest changes in concentrations occurred within 72 h. During this period, biomass C concentrations decreased by about 10% in both amended soils. The dominant source of triggered CO2-C in the first 24 h was glucose, whereas from 24 to 72 h, the mineralization of biomass C and soil organic C (SOC) dominated in both soils. All microbial indicators recovered by the end of the incubation (168 h). The overall taxonomic composition of the soil bacteria was little influenced, but co-occurrence patterns of bacterial communities, analysed using network analysis based on statistically significant correlations, showed that co-occurrence associations in bacterial networks increased during the triggering response.