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

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 (NPP) and associated ecosystem services such as food production and carbon sequestration. Frequently, experimental manipulations of precipitation have linked altered precipitation regimes to changes in NPP. 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 NPP 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 NPP (ANPP) and belowground NPP (BNPP) responses to both the direction and magnitude of precipitation change. Sensitivity (i.e., productivity response standardized by the amount of precipitation change) of BNPP was similar under precipitation additions and reductions, but ANPP 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 ANPP 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 ANPP and BNPP responses may differ, and that ecosystem responses to extreme events might not be predicted from relationships found under moderate environmental changes.Fil: Wilcox, Kevin R.. University of Oklahoma; Estados UnidosFil: Shi, Zheng. University of Oklahoma; Estados UnidosFil: Gherardi, Laureano. Arizona State University; Estados UnidosFil: Lemoine, Nathan P.. State University of Colorado - Fort Collins; Estados UnidosFil: Koerner, Sally E.. University of South Florida; Estados UnidosFil: Hoover, David L.. United States Department of Agriculture. Agricultural Research Service; ArgentinaFil: Bork, Edward. University of Alberta; CanadáFil: Byrne, Kerry M.. Humboldt State University; Estados UnidosFil: Cahill Jr., James. University of Alberta; CanadáFil: Collins, Scott L.. University of New Mexico; Estados UnidosFil: Evans, Sarah. Michigan State University; Estados UnidosFil: Gilgen, Anna K.. Swiss Federal Institute of Technology Zurich; SuizaFil: Holub, Petr. Czech Academy of Sciences; República ChecaFil: Jiang, Lifen. University of Oklahoma; Estados UnidosFil: Knapp, Alan K.. State University of Colorado - Fort Collins; Estados UnidosFil: LeCain, Daniel. United States Department of Agriculture. Agricultural Research Service; ArgentinaFil: Liang, Junyi. University of Oklahoma; Estados UnidosFil: García Palacios, Pablo. Universidad Rey Juan Carlos; EspañaFil: Peñuelas, Josep. Consejo Superior de Investigaciones Científicas. Centre de Recerca Ecológica I Aplicacions Forestals; España. Universitat Autònoma de Barcelona; EspañaFil: Pockman, William T.. University of New Mexico; Estados UnidosFil: Smith, Melinda D.. State University of Colorado - Fort Collins; Estados UnidosFil: Sun, Shanghua. Northwest A & F University; ChinaFil: White, Shannon R.. Government of Alberta; CanadáFil: Yahdjian, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. ; ArgentinaFil: Zhu, Kai. Rice University; Estados Unidos. University of Texas; Estados UnidosFil: Luo, Yiqi. University of Oklahoma; Estados Unido