Global climate change is causing more extreme droughts, as well as subtler chronic changes in precipitation patterns.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. Both chronic and extreme changes in precipitation variability can alter ecosystem structure and function, and these alterations may affect how systems respond to future extreme climate events.We investigated how past precipitation change alters 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) aboveground and belowground in a mesic grassland at the Konza Prairie LTER network site. To do this, we imposed a 2-year extreme drought (66% reduction in ambient growing season precipitation) in two unique grassland precipitation experiments: a long-term (15-year) experiment that chronically increased rainfall variability, and an experiment that imposed a previous short-term (2-year) extreme drought.We measured plant production aboveground and belowground, assessed root depth distribution, and quantified root traits during and after the experimental extreme drought.
Results/Conclusions
We found evidence for strong legacy effects of past precipitation change. Both chronic and extreme precipitation change legacies increased ecosystem sensitivity to extreme drought, especially belowground. A legacy of chronically increased precipitation variability amplified the decline in root biomass production during drought (23% reduction), and a legacy of extreme precipitation change amplified a decline in both aboveground and belowground biomass production (57% and 65% reductions, respectively). Recovery following drought was slower belowground than aboveground.In both experiments, the greatest root declines occurred at shallow soil depths. The dominant species showed the greatest plasticity in specific root length (a key trait associated with drought resistance) and the smallest reduction in root production during drought. Our results emphasize the importance of considering legacy effects of past precipitation changes when assessing the impacts of climate extremes, and of quantifying impacts belowground as well as aboveground. Failure to consider the history of precipitation changes and/or belowground impacts would lead to significant underestimation of ecosystem sensitivity to drought. Understanding how past precipitation changes may alter responses to future extreme droughts will be important for predicting ecosystem sensitivity to a changing climate.