Controls of temporal variability of the soil microbial biomass: A global-scale synthesis

The temporal variability of the soil microbial biomass is an important component of its turnover, and thus contributes to patterns of soil nutrient release and mineralization. I selected 58 previously published studies in which temporal data for soil microbial biomass C and N had been presented, and analyzed this data for underlying trends, by calculating coefficients of variation (standard deviation/mean) over time from each study as a measure of temporal variability. Contrary to expectations, there was no difference in temporal variability among forest, grassland and arable ecosystems, or between tilled and non-tilled arable systems, indicating that increasing disturbance levels does not have destabilizing effects on the microbial biomass. Correlation, partial correlation and stepwise multiple regression analyses between the coefficients of variation and selected soil and macroclimatic variables across the studies I considered showed that temporal variability of biomass C was most closely related to soil N content in forests, pH and latitude in arable ecosystems, and pH, latitude and soil C contents in grasslands. Relationships involving soil C, N and pH were negative; those involving latitude were positive. For the entire data set, temporal variability was best predicted by a three-component model incorporating pH, soil C and latitude. The effects of increasing latitude on increasing temporal variability of biomass C is interpreted in terms of higher latitudes having higher interseasonal variations in temperature, causing greater interseasonal flux of the biomass. The apparent effects of pH and soil C in reducing temporal variation indicates that alleviating stress on the microbial community has stabilizing effects. It is shown that those factors which stabilize the microbial biomass reduce its turnover, and this is likely to have important consequences for soil nutrient dynamics and ultimately plant growth and ecosystem productivity. (C) 1998 Elsevier Science Ltd. All rights reserved.