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

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.