PARENT SESSION
Organized Oral Session 41: Ecological responses to precipitation: Scaling patterns and processes from the genome to the ecosystem
Organizer(s): ME Loik and SD Smith
Thursday, August 11, 8:00 AM - 11:30 AM, Meeting Room 510b, Level 5, Palais des congrès de Montréal
Ecological responses to precipitation quantity and frequency in grasslands: Pattern and process from the gene to the ecosystem.
Fay, Philip*,1, Smith, Melinda2, Travers, Steven3, Nippert, Jesse4, Blair, John3, Garrett, Karen3, 1 Natural Resources Research Institute, Duluth, MN, USA2 Yale University, New Haven, CT, USA3 Kansas State University, Manhattan, KS, USA4 Colorado State University, Ft Collins, CO, USA
ABSTRACT- Grasslands account for 40% of the U.S. land mass and are highly responsive to precipitation variability. Climate models and observations indicate warming and increased temporal variability in rainfall patterns for the grasslands of the central US. To examine the consequences of increased variability in precipitation, growing season rainfall patterns have been manipulated in an eastern Kansas tallgrass prairie since 1998. A more variable rainfall pattern (extended dry intervals, fewer but larger rain events, no change in total rainfall quantity) lowered the mean and increased the variation in 0-30 cm soil water content, and reduced mean total aboveground net primary productivity (ANPP) vs. the ambient rainfall pattern, due to decreased growth of several C4 grasses. Leaf photosynthetic carbon gain in two C4 grasses that account for > 60% of total biomass (Andropogon gerardii, Sorghastrum nutans) was correlated with temporal variation in soil water content (R2 = 0.80), suggesting that these grasses contribute strongly to variation in ecosystem carbon and water fluxes. However, water use efficiency and photosynthetic nitrogen use efficiency of S. nutans decreased more strongly with decreasing soil water content than did that of A. gerardii, suggesting that S. nutans is more negatively affected than A. gerardii by a more variable precipitation regime, a difference borne out in flowering stem density, relative cover and biomass, (0.0001 ≤ p ≤ 0.02). Preliminary analysis of A. gerardii cDNA hybridized to maize microarrays indicated that genes regulating photosystem I/II activity in A. gerardii were differentially up regulated in the more variable rainfall treatment vs. the ambient rainfall treatment, suggesting that compensatory increases in photosynthetic function may explain A. gerardii′s tolerance of increased rainfall variability. A comparative analysis of gene activity in individuals of A. gerardii and S. nutans exposed to long-term rainfall variability treatments is underway. Results to date suggest that ecosystem responses to rainfall variability are based on a combination of genetic, physiological and life history responses in these two dominant grasses.
Key words: grassland, ANPP, climate change, Konza Prairie