Asymmetric responses of primary productivity to precipitation extremes: A synthesis of grassland precipitation manipulation experiments

<jats:title>Abstract</jats:title><jats:p>Climatic changes are altering Earth's hydrological cycle, resulting in altered precipitation amounts, increased interannual variability of precipitation, and more frequent extreme precipitation events. These trends will likely continue into the future, having substantial impacts on net primary productivity (<jats:styled-content style="fixed-case">NPP</jats:styled-content>) and associated ecosystem services such as food production and carbon sequestration. Frequently, experimental manipulations of precipitation have linked altered precipitation regimes to changes in <jats:styled-content style="fixed-case">NPP</jats:styled-content>. Yet, findings have been diverse and substantial uncertainty still surrounds generalities describing patterns of ecosystem sensitivity to altered precipitation. Additionally, we do not know whether previously observed correlations between <jats:styled-content style="fixed-case">NPP</jats:styled-content> and precipitation remain accurate when precipitation changes become extreme. We synthesized results from 83 case studies of experimental precipitation manipulations in grasslands worldwide. We used meta‐analytical techniques to search for generalities and asymmetries of aboveground <jats:styled-content style="fixed-case">NPP</jats:styled-content> (<jats:styled-content style="fixed-case">ANPP</jats:styled-content>) and belowground <jats:styled-content style="fixed-case">NPP</jats:styled-content> (<jats:styled-content style="fixed-case">BNPP</jats:styled-content>) responses to both the direction and magnitude of precipitation change. Sensitivity (i.e., productivity response standardized by the amount of precipitation change) of <jats:styled-content style="fixed-case">BNPP</jats:styled-content> was similar under precipitation additions and reductions, but <jats:styled-content style="fixed-case">ANPP</jats:styled-content> was more sensitive to precipitation additions than reductions; this was especially evident in drier ecosystems. Additionally, overall relationships between the magnitude of productivity responses and the magnitude of precipitation change were saturating in form. The saturating form of this relationship was likely driven by <jats:styled-content style="fixed-case">ANPP</jats:styled-content> responses to very extreme precipitation increases, although there were limited studies imposing extreme precipitation change, and there was considerable variation among experiments. This highlights the importance of incorporating gradients of manipulations, ranging from extreme drought to extreme precipitation increases into future climate change experiments. Additionally, policy and land management decisions related to global change scenarios should consider how <jats:styled-content style="fixed-case">ANPP</jats:styled-content> and <jats:styled-content style="fixed-case">BNPP</jats:styled-content> responses may differ, and that ecosystem responses to extreme events might not be predicted from relationships found under moderate environmental changes.</jats:p>