Deconstructing precipitation variability: Rainfall event size and timing uniquely alter ecosystem dynamics

• Published in: The Journal of ecology 2021-09, Vol.109 (9), p.3356-3369
• Main Authors: Griffin‐Nolan, Robert J., Slette, Ingrid J., Knapp, Alan K.
• Format: Article
• Language: English
• Subjects: Arid lands; Arid zones; Aridity; Atmospheric precipitations; Carbon dioxide; Climate change; Community composition; Dynamics; Ecosystem dynamics; ecosystem functioning; Ecosystems; Fluctuations; Grasses; Grasslands; Growing season; Herbivores; multifunctionality; net primary production; Net Primary Productivity; Physiological responses; Plant communities; Precipitation; precipitation variability; Primary production; pulse dynamics; Rain; Rainfall; Seasonal variation; Seasonal variations; Seasons; semi‐arid ecosystems; Soil; soil CO2 flux; Soil moisture; Variability; Water stress
• ISSN: 0022-0477; 1365-2745
• DOI: 10.1111/1365-2745.13724

Water‐limited ecosystems are highly sensitive to not only precipitation amount, but also precipitation pattern, particularly variability in the size and timing of growing season rainfall events. Both rainfall event size and timing are expected to be altered by climate change, but the relative responses of dryland ecosystems to changes in rainfall event size versus timing have not been resolved. Here, we disentangle the effects of these different aspects of precipitation pattern on ecosystem dynamics. We experimentally assessed how these two aspects of rainfall variability impacted a semi‐arid grassland ecosystem by altering an ambient precipitation pattern to eliminate variability in (a) rainfall event size (all events were made the same size), (b) rainfall event timing (all events were uniformly spaced in time) and (c) both. Total precipitation amount was constant for all treatments. We measured responses of soil moisture, ecosystem carbon flux (e.g. net primary production and soil CO2 flux), plant community composition and physiological responses of the dominant C4 grass, Bouteloua gracilis. Removing variability in rainfall event size altered ecosystem dynamics more than a pattern of uniform event timing, but the largest impact occurred when variability in both were removed. Notably, eliminating variability in both event size and timing increased above‐ground net primary productivity by 23%, consistent with reduced water stress in the dominant C4 grass, while also reducing seasonal variability in soil CO2 flux by 35%, reflecting lower seasonal variability in soil moisture. Synthesis. Unique responses to different aspects of precipitation variability highlight the complexity of predicting how dryland ecosystems will be affected by climate change‐induced shifts in rainfall patterns. Our results provide novel support for the key roles of rainfall event size and timing, in addition to total precipitation amount, as determinants of ecosystem function. We reproduced the exact precipitation pattern of a past growing season in a semi‐arid grassland and deconstructed this pattern to eliminate variability in (a) rainfall event size, (b) timing or (c) both. Unique ecological responses to different aspects of precipitation variability highlight the complexity of predicting how dryland ecosystems will be affected by climate change‐induced shifts in rainfall patterns.