1. CLIMATE CHANGE EFFECTS ON SOIL CO 2 AND CH 4 FLUXES IN FOUR ECOSYSTEMS ALONG AN ELEVATIONAL GRADIENT IN NORTHERN ARIZONA Joseph C. Blankinship 1, James R. Brown 1, Paul Dijkstra 1,2, Bruce A. Hungate 1,2 Significance Methods Results Implications 1 Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011; 2 Merriam-Powell Center for Environmental Research, Flagstaff, AZ, 86011 E-mail of corresponding author: joseph.blankinship@nau.edu Carbon dioxide (CO 2 ) and methane (CH 4 ) are important greenhouse gases that contribute to global warming, but little is known about how predicted interactive changes in temperature and precipitation will affect soil fluxes in different ecosystems. Globally, heterotrophic soil organisms and plant root respiration release about 85 Pg (10 15 g) of CO 2 -C into the atmosphere annually, and high-affinity methane-oxidizing bacteria consume about 30 Tg (10 12 g) of CH 4 -C from the atmosphere annually (IPCC 2001). 1.Will predicted magnitudes of warming and altered precipitation affect soil CO 2 production and CH 4 consumption? 2.Will responses depend on interactions between warming and altered precipitation? 3.Will responses depend on ecosystem type? Merriam Climatic Change Experiment Aboveground Biomass (no grazing allowed) Soil (organic & mineral) Roots Microorganisms Macrofauna Leachate Collector mixed conifer forest mixed conifer forest precip.= 790 mm y -1 mean annual T = 4.0°C ponderosa pine forest ponderosa pine forest 660 mm y -1 piñon-juniper woodland piñon-juniper woodland 380 mm y -1 high desert grassland high desert grassland 230 mm y -1 Great Basin desert Great Basin desert 180 mm y -1 mean annual T = 10.0°C +1.5°C Flagstaff, AZ (est. 2002) 3-way complete factorial design (n=6 or 7) : 4 4 ecosystems 2 2 temperatures (ambient and elevated) through elevational transplantation 3 3 precipitations (-30%, ambient, and +50%) through rainout shelters and funnels 30 cm diameter 30 cm deep el. 2615 m el. 1540 m All cores were taken from grassy interspaces to standardize vegetation type and shading effects soil type = loam sandy loam loam clay PVC lysimeter 160 total lysimeters Soils were sampled in Sept 2005, 3 years after treatments began Harvest Soils Hour 0Hour 48 sieve, weigh into bottles (adjust water content) HEADSPACE SAMPLE #1 Start Incubations HEADSPACE SAMPLE #3 Finish Incubations Hour 96 Concentration Time Laboratory Measurements net CH 4 consumption Incubation conditions: Warm (25°C), Dark, Unshaken Standardized moisture (35% WHC) Elevated [CH 4 ] (10x ambient, 18 ppm) Hour 60 HEADSPACE SAMPLE #2 gas chromatograph 0-20 cm deep cores 12 ml gas storage vials 250 ml bottles CO 2 production Flagstaff, Arizona, USA Actual CO 2 and CH 4 fluxes measured monthly between Aug – Oct 2005, three years after treatments began Laboratory CO 2 and potential CH 4 fluxes measured in Sept 2005, three years after treatments began CO 2 CH 4 Actual rates of CO 2 production were precipitation-limited, regardless of ecosystem type. Actual rates of CH 4 consumption were negatively affected by precipitation, regardless of ecosystem type, suggesting that all ecosystems were vulnerable to diffusional limitation. Potential rates of CH 4 consumption suggest that the wettest mixed conifer forest was especially vulnerable to diffusional limitation by elevated precipitation, or that methanogenesis increased. (* indicates significant effect) The effect of temperature on actual rates of CO 2 production depended on ecosystem type. (* indicates significant effect) Laboratory rates of CO 2 production suggest that the positive effect of warming in the coldest ecosystem is mediated by water availability. (* indicates significant effect) The effect of temperature on actual rates of CH 4 consumption depended on ecosystem type. The mixed conifer forest and high desert grassland tended to be positively affected by warming, and the piñon-juniper woodland tended to be negatively affected. The effect of temperature on potential rates of CH 4 consumption also depended on ecosystem type. The mixed conifer forest and high desert grassland were positively affected by warming, and the piñon-juniper woodland and ponderosa pine forest were negatively affected. (* indicates significant effect) 1.In a wetter world, these soils become a larger source of CO 2 and a smaller sink of CH 4 (positive feedbacks to global warming).  CH 4 consumption was most sensitive to elevated precipitation in the wettest ecosystem, probably because of lower rates of atmospheric CH 4 diffusion or higher rates of O 2 consumption through respiration 2.Interactions between climate change factors and between ecosystems can mediate changes in soil CO 2 and CH 4 fluxes.  A 3-way interactive effect (ecosystem x temp x precip) suggests that soil respiration is only temperature-limited in colder ecosystems when supplied with enough precipitation 3.Ecosystem type is most important for predicting temperature effects.  Probably mediated by relative water availability  Positive effects of warming were most consistent in the coldest ecosystem Time net CH 4 consumption CO 2 production Concentration 0 min20 min40 min