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Effect of Drought on Wetland Microbial Processes

Effect of Drought on Wetland Microbial Processes. Freeman et al 1995. Man’s influence on freshwater ecosystems and water use. IAHS Pub. No. 230:199-206. Drought wetland. Control wetland. Peat sample. Peat sample. River. Activity measurements on peat and biofilm samples.

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Effect of Drought on Wetland Microbial Processes

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  1. Effect of Drought on Wetland Microbial Processes Freeman et al 1995. Man’s influence on freshwater ecosystems and water use. IAHS Pub. No. 230:199-206

  2. Drought wetland Control wetland Peat sample Peat sample River

  3. Activity measurements on peat and biofilm samples • Electron transport system (ETS) • Poly-β-OH-alkanoate (bacterial storage product - nutritional status indicator) • Chlorophyll • Nutrients in water

  4. Control Drought-simulated Activity 85% higher 74% Wetland Biofilm ETS Activity

  5. Dissolved organic and inorganic nutrients Control Drought-simulated 26% lower Concentration 57% higher Organics Inorganics

  6. Chlorophyll and PHA Control Drought-simulated 145% higher Concentration 51% lower Organics Inorganics

  7. Summary • Suppression of microbial activity in wetland during drought • Consume less inorganic nutrients • Drought stresses plants, reduces their release of DOC, which in turn reduced amount available for microbial activity • Stream microbial activity responds to nutrient levels in water from wetland

  8. Carbon cycle feedbacks: effects of microbial processes on climate change Bardgett et al. 2008. The ISME Journal. 2:805-813

  9. CO2, CH4, N2O CO2 ? Corg Land CO2 oceans CaCO3 Carbon cycle feedback

  10. Amounts of greenhouse gases in air • For every 1,000,000,000 air molecules • 375,000 molecules of carbon dioxide • 2,000 molecules of methane • <1,000 molecules of nitrous oxide • <1 molecule of chlorofluorocarbon • Carbon dioxide accounts for 62% of radiative forcing by all long-lived greenhouse gases

  11. Climate change Direct feedback temperature extreme events Indirect feedback elevated CO2 temperature precipitation CO2 Autotrophic respiration Net primary production Nutrient cycle feedback rhizodeposits litter Heterotrophic respiration Microbial biomass Soil fauna DOC Bardgett et al. 2008. Isme J. 2:805-813

  12. Role of forests in climate stability • Forests, like oceans have the ability to remove CO2 from atmosphere • The amount of carbon stored in temperate and boreal soil is 4x that stored in plant biomass and 33% higher than total carbon storage in tropical forests. • Biochemically stable or mineral-bound C • Sequestration of root-derived carbon in soil • used stable isotope natural abundance technique

  13. 0 100 200 300 CO2 umol/mol added to ambient Plant response to CO2 • In all plant species tested, an increase in CO2 resulted in a reduction in maximum photosynthetic rate ( ), an increase in net photosynthetic rate ( ), and an increase in total biomass ( )

  14. Microbial response to CO2 • Carbon sequestration by soil ( ) decreased as CO2 concentration in air increased • This was related to increase in soil bacterial respiration rate ( ) • associated with root-derived sugars from exudate • total microbial biomass was unaffected 0 100 200 300 CO2 umol/mol added to ambient

  15. Increase in CO2 concentration in atmosphere has the potential to trigger a large positive feedback on the rate of increase in global atmospheric CO2 concentration and associated global climate change CO2 CO2 glucose exudation respiration

  16. Summary • Net effect of climate change on ecosystem carbon budgets depends on balance between photosynthesis and respiration • Direct feedbacks • Soil organic matter decomposition and CO2 production • Indirect feedbacks • Plant growth effects on DOC release in soil and effect of this on microbial respiration • Effets on microbial community structure and function (activity)

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