Drought resistance and resilience: The role of moisture-plant interactions and legacies in a dryland ecosystem

Authors: Hoover, David; PFENNIGWERTH, ALIX - Us Geological Survey (USGS); DUNIWAY, MICHAEL - Us Geological Survey (USGS)

Submitted to: Journal of Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2021
Publication Date: 5/3/2021
Citation: Hoover, D.L., Pfennigwerth, A., Duniway, M. 2021. Drought resistance and resilience: The role of moisture-plant interactions and legacies in a dryland ecosystem. Journal of Ecology. 109:3280-3294. https://doi.org/10.1111/1365-2745.13681.
DOI: https://doi.org/10.1111/1365-2745.13681

Interpretive Summary: Climate change is expected to lead to more droughts, which may vary in their seasonal timing. In this study we examined the effects of seasonal drought timing in a dryland ecosystem using an experiment with three rainfall treatments (control, warm-season drought, and cool-season drought) in two plant communities (grasses with or without shrubs). We were specifically interested in the effects of drought both during and after the event on soil moisture, plant phenology and biomass. During the drought, soil moisture decreased, which affected plant growth by either delaying green-up or speeding up aging and reducing plant biomass. We also observed the effects of drought persisted long after the drought ended. These 'legacy effects' were complicated and involved feedbacks between soil moisture and plants. The results of this study highlight the interactions between soil moisture and plants both during and after drought.

Technical Abstract: Climate change is projected to reduce water availability through changes in the hydrological cycle, including more frequent and intense droughts, as well as seasonal shifts in precipitation. In water-limited ecosystems, such as drylands, lower soil water availability may exceed the adaptive capacity of many organisms, leading to cascading ecological effects during (concurrent effects) and after drought (legacy effects). The concurrent and legacy effects of drought may depend on drought magnitude, timing, and the resistance and resilience of the ecosystem. Here, we investigated the effects of drought seasonality and plant community on two dominant perennial grasses in a dryland ecosystem. The experiment consisted of three precipitation treatments (ambient precipitation, warm-season drought, cool-season drought), applied in two plant communities (grasses with or without a large shrub), over a three-year period. We examined the concurrent and legacy effects of seasonal drought on soil moisture dynamics and the phenology and biomass of a cool-season (C3 photosynthesis) and a warm-season grass (C4¬ photosynthesis). Drought treatments had strong concurrent effects on soil moisture, with the greatest reductions in the shallow soil layers and occurring for roughly 50% of treatment duration. Drought legacy effects on soil moisture manifested as either negative soil moisture legacies persisting once seasonal drought treatments ended, or as positive soil moisture legacies emerging months later. Drought reduced growing season length by delaying green-up (cool-season drought) or advancing senescence (warm-season drought), and reduced biomass for both species. Biomass and phenology legacy effects from drought emerged in the second and third years of the experiment. While we observed differential sensitivity to drought seasonality between the two grasses, we found limited evidence that shrub presence had interactive effects with the drought treatments. Overall, this study also revealed how the complicated interactions between soil moisture and plants influence the concurrent and legacy effects of drought.