Response of secondary production and its components to multiple stressors in nematode field populations.
Realistic measures of the impact of individual or multiple stressors are important for ecological risk assessment. Although multiple anthropogenic stressors are common in human-dominated environments, knowledge of their influence on functional population parameters such as secondary production (P) and biomass turnover (P/B) is very limited. Secondary production integrates population characteristics such as biomass, size-frequency distribution and body growth rate, and provides a link between population and system ecologies. The influence of copper and pH stress on yearly secondary production and biomass turnover of field populations of the nematode Acrobeloides nanus was investigated. The responses of the components of secondary production were also analysed to elucidate the mechanisms underlying the change in secondary production. Secondary production and biomass turnover showed reduced values in soil of low pH. A negative effect of copper on both parameters was observed only when the copper load was combined with low pH, otherwise higher copper concentrations resulted in higher secondary production and biomass turnover. The observed response of production and biomass turnover was mainly driven by changes in mean relative growth rate (MRGR), a measure of body growth rate estimated in a laboratory soil experiment. The biomass was higher on average in the plots with high copper load, while there was no significant response to pH. Our results demonstrate that populations of soil organisms may experience strong synergistic effects of combined stressors (acidification and copper stress) on functional population parameters while showing no detrimental effects on biomass. Moreover, the effects on secondary production and biomass turnover rate are predominantly driven by effects on body growth rate. We recommend that ecological risk assessment methodologies should include consideration of soil contamination on the basis of conservation of functional properties of ecosystems and their key components.