|Williams, David -|
|Pendall, Elise -|
Submitted to: Ecological Society of America Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 10, 2009
Publication Date: August 1, 2009
Citation: Morgan, J.A., Lecain, D.R., Booth, D.T., Blumenthal, D.M., Williams, D.G., Pendall, E., Dijkstra, F.A., Smith, D.P., Kimball, B.A., West, M.S. 2009. Aboveground productivity of C3 and C4 perennial grasses are differentially affected by elevated CO2 and warming in a Wyoming northern mixed-grass prairie. Ecological Society of America Proceedings. COS 38-5. Technical Abstract: Responses of North American Great Plains grasslands to global change are uncertain, due in part to differing physiologies of dominant C3 and C4 grasses. Warmer temperatures would presumably favor warm-season, C4 grasses, while rising CO2 would benefit C3 species, whose photosynthetic apparatus is CO2-unsaturated at present-day levels of CO2. The Prairie Heating and CO2 Enrichment (PHACE) experiment tests the interactive effects of rising CO2 (present ambient [380 ppm], and elevated [600 ppm] CO2) and elevated temperature ([1.5/3.0 ºC warmer day/night]) on the ecology of the northern mixed grass prairie (n=5). Aboveground plant biomass (AGB) was measured in late July each year, and plant/litter/ground cover measured with photography throughout the growing season. Soil water content was monitored continuously in each plot with Sentek soil moisture probes. Results are presented for 2006 (CO2 enrichment alone), and 2007 and 2008 (CO2 enrichment plus warming). Elevated CO2 enhanced total mid-season AGB (2006-2008), although warming eliminated this response in 2008. Aboveground biomass of both C3 and C4 grasses were enhanced under CO2-enrichment (2006), although warming eliminated the CO2-induced AGB response of C3 grasses in 2008. In contrast, the enhancement of C4 AGB by CO2 enrichment was more evident in the warmed treatment. Seasonal measurements of plant cover showed similar response patterns as AGB. Repeated measurements within each growing season showed that seasonal soil water dynamics and differences in plant phenology affected the relative expression and timing of cover responses between the C3 and C4 grasses. Soil water content was often enhanced under elevated CO2, reduced under warming, and intermediate in the ambient CO2/non-warmed and elevated CO2/warmed treatments. The results suggest that long-term changes in productivity and species composition in mixed-grass prairie will be determined by a complicated interaction involving direct responses to CO2 and temperature and indirect responses mediated by changes in soil water dynamics.