Precipitation temporal repackaging into fewer, larger storms delayed seasonal timing of peak photosynthesis in a semi-arid grassland

Authors: ZHANG, F. - University Of Arizona; Biederman, Joel; PIERCE, N.A. - University Of Arizona; POTTS, D.L. - State University Of New York (SUNY); DEVINE, C.J. - University Of Arizona; HAO, Y.B. - University Of Chinese Academy Of Sciences; SMITH, W - University Of Arizona

Submitted to: Functional Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2021
Publication Date: 12/8/2021
Citation: Zhang, F., Biederman, J.A., Pierce, N., Potts, D., Devine, C., Hao, Y., Smith, W. 2021. Precipitation temporal repackaging into fewer, larger storms delayed seasonal timing of peak photosynthesis in a semi-arid grassland. Functional Ecology. 36(3):646-658. https://doi.org/10.1111/1365-2435.13980.
DOI: https://doi.org/10.1111/1365-2435.13980

Interpretive Summary: Against a backdrop of rising temperature, large portions of the western United States are experiencing fewer, larger, and less frequent rain storms. We do not know how this intensification of rainfall patterns may affect the amount and timing of photosynthesis by drylands plants, but this is important for decisions made in ranching, land management and carbon cycle science. Here we conducted a field experiment which excluded natural rainfall and replaced it with irrigation in fewer, larger simulated rainstorms, while keeping the total amount the same over the summer growing season. We found that repackaging rainfall into few, large storms delayed the timing of peak plant photosynthesis but up to one month. Meanwhile, the magnitude of greatest weekly photosynthesis was not affected. Future management decisions should consider the delay in peak productivity shown here for optimal use and timing of grassland resources.

Technical Abstract: Against a backdrop of rising temperature, large portions of the western United States are experiencing fewer, larger, and less frequent precipitation events. How such temporal ‘repackaging’ of precipitation alters the magnitude and timing of seasonal maximum gross primary productivity (GPPmax) remains unknown. Addressing this knowledge gap is critical, since changes to GPPmax magnitude and timing can impact a range of ecosystem services and management decisions. Here we used a field-based precipitation manipulation experiment in a semi-arid mixed annual/perennial bunchgrass ecosystem to investigate how temporal repackaging of a fixed total seasonal precipitation amount impacts seasonal GPPmax and its timing. We found that temporal repackaging of precipitation profoundly influenced the seasonal timing of GPPmax. Many/small precipitation events advanced the seasonal timing of GPPmax by ~13 days in comparison with climatic normal precipitation. Conversely, few/large events led to deeper soil water infiltration, which delayed the timing of GPPmax by up to 16 days in comparison with climatic normal precipitation, and altered end-of-season community composition by increasing the diversity of shallow-rooted annual plants. While GPPmax magnitude did not differ across precipitation treatments, it was positively correlated with the abundance and biomass of deeper-rooted perennial bunchgrasses. Our results suggest that temporal repackaging of precipitation into fewer/larger events postpones the seasonal GPPmax of semi-arid grasslands due to the slower growth response of perennial grasses to soil moisture changes and the increases of annual plant diversity. The timing and magnitude of precipitation events and resulting temporal patterns of soil moisture relative to critical times for plant growth, biomass accumulation, and plant life histories may regulate ecosystem responses to altered precipitation patterns. Our results show how semi-arid grasslands could be expected to respond to already-observed and model-forecasted shifts to intensification of the hydrologic cycle and more extreme-duration drought.