Extreme climate events such as droughts are becoming more frequent and intense. Concurrently, precipitation patterns are also changing in more gradual but chronic ways. Research to date has tended to study ecological responses to chronic and extreme climatic changes independently, despite recognition that they are occurring simultaneously and are likely to interact. Altered ecosystem structure and function resulting from chronic or extreme precipitation changes may alter the impacts of future extreme climate events.We investigated how past precipitation changes alter the impact of extreme drought on net primary productivity (a key aspect of ecosystem carbon cycling with the potential to feed back to atmospheric drivers of climate change) in a mesic grassland at the Konza Prairie LTER site. We experimentally imposed extreme droughts (66% reduction in ambient growing season precipitation for two years) on experiments which previously altered precipitation patterns and amounts, and we measured plant production both aboveground and belowground during and after these extreme droughts.
Results/Conclusions
We found evidence for strong legacy effects of past precipitation change, especially belowground. We found that extreme drought significantly reduced biomass production, and that both chronic and extreme precipitation change legacies amplified the negative response of production to extreme drought. A legacy of past extreme change decreased production more than a legacy of past chronic precipitation alteration (65% vs. 23% reduction in root biomass production, respectively). We also found that recovery following extreme drought was slower belowground than aboveground.Our results suggest that more extreme droughts will cause increasingly larger reductions in productivity, especially belowground. The difference in belowground vs. aboveground productivity patterns suggests that belowground responses cannot be reliably predicted from aboveground responses. Failing to consider legacy effects of past precipitation change, and/or ignoring changes occurring belowground would lead to significant underestimation of the impacts of extreme droughts. Understanding these asymmetric drought legacies will be important in understanding ecosystem responses to a changing climate.