Arid ecosystem responses to variations in the frequency and magnitude of growing season precipitation

TitleArid ecosystem responses to variations in the frequency and magnitude of growing season precipitation
Publication TypeConference Paper
Year of Publication2004
AuthorsSnyder K.A., Cable J.M., Huxman T.E., Tartowski S.
Conference Name89th Annual Meeting, Ecological Society of America
Date PublishedAugust 1, 2004
Conference LocationPortland, OR
ARIS Log Number168819
Keywordsarid systems, climate change, ecosystem responses, growing season precipitation
AbstractGlobal climate change models predict regional changes in average seasonal precipitation, but few models or experiments address how changes in the delivery of precipitation within the growing season will affect ecosystem responses. Arid systems differ from mesic systems in that water availability is frequently low enough to severely restrict biological activity. Consequently, the frequency and magnitude of precipitation events, which dictate the length and severity of intervening dry periods, may have substantial effects on ecosystem function regardless of the total amount of seasonal rainfall. We examined how a 60 mm increase in summer precipitation (46% increase over mean summer rainfall) applied with two different frequencies and magnitudes during the growing season affected carbon, water and nitrogen dynamics of a Chihuahuan Desert scrub ecosystem. Plots containing mesquite (Prosopis glandulosa) and black grama grass (Bouteloua eriopoda) were assigned to either: ambient precipitation (controls), ambient plus frequent small (5-6 mm) rainfall events applied weekly, and ambient plus infrequent large (20-24 mm) events applied monthly. Mesquite used rainfall from 5 mm and 24 mm storms, as evidenced by increased stem elongation, improved water status and uptake of deuterium-labeled rainfall, but mesquite response was greater under large infrequent rainfalls. Daytime measurements of net ecosystem carbon exchange on subplots containing soil, plant roots and biological soil crusts indicated biological soil crust photosynthesis was improved by frequent small rainfalls. Keeling plot analyses of d13C of respired CO2 during dark hours indicated that the contribution from different sources (roots, microbes and soil crusts) varied with rainfall treatment. Both infrequent large rainfalls and frequent small rainfalls significantly increased nitrogen availability, especially in the surface soil. We found that changes in the depth and duration of soil wetting, resulting from different precipitation patterns, have important implications for ecosystem carbon and nitrogen dynamics because of the differential sensitivity of ecosystem components.