Effects of compounded precipitation pattern intensification and drought occur belowground in a mesic grassland

Authors: SLETTE, INGRID - Colorado State University; BLAIR, JOHN - Kansas State University; Fay, Philip; SMITH, MELINDA - Colorado State University; KNAPP, ALAN - Colorado State University

Submitted to: Ecosystems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2021
Publication Date: 10/20/2021
Citation: Slette, I.J., Blair, J.M., Fay, P.A., Smith, M.D., Knapp, A.K. 2021. Effects of compounded precipitation pattern intensification and drought occur belowground in a mesic grassland. Ecosystems. https://doi.org/10.1007/s10021-021-00714-9. https://doi.org/10.1007/s10021-021-00714-9.
DOI: https://doi.org/10.1007/s10021-021-00714-9

Interpretive Summary: Climate change is altering precipitation regimes globally, with expectations of intensified precipitation- frequent long dry periods interspersed with periods of heavy rainfall. The potential impacts of altered precipitation regimes remain challenging to predict. In a central U.S. grassland, ARS scientists and university collaborators conducted an experiment that imposed an extreme 2-yr drought (66% reduction in growing season precipitation) on plots with a 16-year history of experiencing intensified precipitation and control plots experiencing the current precipitation pattern. The results revealed that compounded precipitation changes – an extreme multiyear drought following a long period of intensified precipitation - may lead to unique but “hidden” (i.e., belowground) responses in grasslands. The history of intensified precipitation patterns amplified drought-induced reductions in root mass and length production by subdominant members of the plant community and also reduced soil CO2 flux responses to precipitation events both during and after drought. These changes have potentially important consequences for ecosystem carbon cycling and storage.

Technical Abstract: Climate change is altering precipitation regimes globally, with expectations of intensified precipitation patterns (e.g., larger but fewer rainfall events) and more frequent and extreme droughts. Although both dimensions of precipitation change have been shown to impact ecosystem function individually, it is more likely that they will occur in combination. The potential compounded impacts of these climatic changes remain to be evaluated. In a central U.S. grassland, we imposed an extreme 2-yr drought (66% reduction in growing season precipitation) on plots with a long-term (16-yr) history of experiencing intensified precipitation patterns (3-fold increase in event size and 3-fold decrease in event number during the growing season). While this intensified pattern did not alter total precipitation amount, it generally led to ecosystem responses consistent with a drier environment (e.g., reduced aboveground net primary production, drier shallow soils, and reduced soil CO2 flux). However, this history of intensified precipitation patterns did not affect aboveground net primary production responses to extreme drought. In contrast, previous exposure to more intense precipitation patterns amplified drought-induced reductions in root mass and length production and also reduced soil CO2 flux responses to precipitation events both during and after drought. Root production responses were driven not by the strongly dominant C4 grass species, Andropogon gerardii, but collectively by the subdominant species in the plant community. Overall, these results reveal that compounded precipitation changes may lead to unique but “hidden” (i.e., belowground) responses in grasslands, with potentially important consequences for ecosystem carbon cycling and storage.