Differential phenological responses of plant functional types to the temporal repackaging of precipitation in a semiarid grassland

Authors: ZHANG, F. - University Of Arizona; Biederman, Joel; DEVINE, C.J. - University Of Arizona; Pierce, Nathan; YAN, D - China Renewable Energy Engineering Institute; POTTS, D.L. - Buffalo State College; SMITH, W.K. - University Of Arizona

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/2025
Publication Date: 2/28/2025
Citation: Zhang, F., Biederman, J.A., Devine, C., Pierce, N.A., Yan, D., Potts, D., Smith, W. 2025. Differential phenological responses of plant functional types to the temporal repackaging of precipitation in a semiarid grassland. Plant and Soil. https://doi.org/10.1007/s11104-025-07323-8.
DOI: https://doi.org/10.1007/s11104-025-07323-8

Interpretive Summary: Many portions of the semiarid US Southwest are receiving rainfall that is repackaged into fewer but larger rain storms, regardless of any trends in the total seasonal or annual rainfall amounts. This rainfall repackaging has unknown consequences for the phenology of rangeland ecosystems including green-up timing, growing season length, and brown-down timing at the end of the growing season. Furthermore, rangeland ecosystems are often composed of different plant types that may each respond differently. In this work, we used rainout shelters at the USDA-ARS rangeland experimental facility RainMan to measure how repackaging a fixed growing season rainfall amount of 205 into fewer/larger rainfall events impacted phenology, which was measured daily by automated cameras. We found that fewer/larger rainfalls delayed green-up after first rainfall by an average of 22 days. This was mainly because shallow-rooted annual grasses failed to thrive under few/large rainfalls, whereas deep-rooted perennial grasses thrived on deeply-infiltrated soil moisture but were slower to respond after the onset of first rainfall. Fewer/larger rainfalls increased the growing season length for perennial grasses and shortened it for annual grasses. These results imply that regardless of rainfall totals, climate change through rainfall repackaging is likely to increase the relative importance of deeper-rooted perennial plants at the expense of shallow-rooted annual plants.

Technical Abstract: Aims - Large portions of the western United States have witnessed extended dry intervals between rainfall events due to an intensified hydrological cycle triggered by global warming. Semiarid ecosystems in these regions are particularly susceptible to temporal repackaging of rainfall, but how such rainfall repackaging alters plant phenology remains unknown. Methods - We examined the effects of rainfall temporal repackaging during the growing season (July–September, from frequent/small events to infrequent/large events, with constant total seasonal rainfall) on plant phenology through a manipulative experiment in a semiarid grassland ecosystem. Using automated high-frequency digital photography, we monitored canopy and plant greenness at both the plot and plant functional type levels, and derived phenological metrics including the start, end and length of the growing season. Results - We found that canopy onset was delayed by 17 to 24 days under infrequent/large events compared to normal historical pattern, with no significant differences among these treatments in canopy descent or growing season length. The phenology metrics of plant functional types showed opposite responses to rainfall repackaging. Perennial grasses had a longer growing season, while annuals had a shorter season under infrequent/large events compared to frequent/small events. Furthermore, growing season length of perennial grasses responded more strongly to deep than shallow soil water conditions. Conclusions - Our analysis demonstrates the potential of high-frequency plant monitoring to enhance our fundamental understanding of community composition and ecological processes that shape semiarid ecosystem responses to rainfall temporal repackaging and its implications for global biogeochemical cycling.