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Impact of varied precipita/on and N deposi/on on grassland soil microbial communi/es and GHG flux Emma L. Aronson Allison lab UC Irvine Soil Respira/on (CO2) • CO2 is the most abundant anthropogenic greenhouse gas (GHG) • CO2 is responsible for most global warming • In soil, CO2 released by microbial, animal, and tree root respira/on Methane (CH4) • Methane (CH4) responsible for >20% of global warming • Holds 25x as much heat as carbon dioxide (CO2) • 200x less CH4 in the atmosphere than CO2, with erra/c increase Methane (CH4) • Methanotrophs ‐ methane oxidizing bacteria ‐ need oxygen ‐ dominant in unsaturated soil • Methanogens ‐ methane producing archaea ‐ cannot live in oxygen ‐ dominant in saturated soil Nitrous Oxide (N2O) • Responsible for ~6% of global warming • Rising due to: – Increased fer/liza/on of agricultural systems – Increased industrial and automo/ve release – N leaching and deposi/on because of 1st 2 causes Nitrous Oxide (N2O) • Greater N fer/liza/on and deposi/on on soil increase N cycling • N addi/on s/mulates increased nitrifica/on and denitrifica/on, which both release N2O 16S Bacterial Community Analysis • 16S gene is conserved in bacteria, coding for part of the ribosome • Commonly used for molecular‐based OTU iden/fica/on • Used to build phylogene/c trees of microbial communi/es 454 Sequencing • Sequencing bacterial 16S • Same procedure as we are doing for leaf li\er • 454 Allows for the genera/on of long read lengths, up to 450bp • No need for cloning! Quan/ta/ve PCR • Quan/ta/ve PCR (qPCR) is used to quan/fy a gene of interest • In this case I will focus on genes for: – Methanotrophy (pmoA) – N2O produc/on (nirS, nirK & nosZ) Hypotheses • I hypothesize that Loma Ridge treatments have changed soil microbial communi/es • Soil moisture & inorganic N status influence: – Soil respira/on, – CH4 consump/on rates, and – N2O release rates – Bacterial community composi/on Expected Outcomes Decreased Rainfall Control Increased Rainfall Indicates rate of CO2 and N2O release, opposite effect on CH4 consump/on Indicates level of soil microbial biodiversity Expected Outcomes N Added N N N N Control N N Indicates rate of CO2 and N2O release, opposite effect on CH4 consump/on Indicates level of soil microbial biodiversity Methods: Greenhouse Gas Fluxes • Measuring CO2 flux at a high temporal resolu/on: – We have 8 auto‐chambers deployed for con/nuous field measurement of CO2 fluxes – There is one auto‐chamber in each treatment combina/on sub‐plot Methods: Greenhouse Gas Fluxes • Measuring CO2, CH4 and N2O fluxes at a high spa/al resolu/on: – Chamber bases implanted in all 48 sub‐plots in the Loma grassland experiment – Gas flux data collected with chambers weekly to monthly – These gas samples are run on gas chromatographs for CH4, CO2 and N2O flux Methods: Soil Microbe Community • On gas sampling dates, surface soil is also collected and frozen in the field. • I will study soil microbial community by: DNA Extrac/on 16S PCR qPCR Nitrifiers 454 Sequencing Methanotrophs Denitrifiers Results: N Treatment • October 28, 2011, measured all 48 plots • Increased N2O release in N treated plots rela/ve to control; no impact on CO2 and CH4 N2O CO2 CH4 P < 0.077 P < 0.451 P < 0.288 Results: H2O Treatments • October 28, 2011, measured all 48 plots • Decreased CO2 release in + & ‐ H2O treatment plots rela/ve to control • No impact on N2O and CH4 N2O CO2 CH4 P < 0.574 P < 0.076 P < 0.860 Ini/al Outcomes Decreased Rainfall Control Increased Rainfall Indicates rate of CO2 release Trends were not seen in N2O release and CH4 consump/on Ini/al Outcomes N Added N N N N Control N N Indicates rate of N2O release Trends were not seen in CO2 release and CH4 consump/on