Effect of drought on wetland microbial processes
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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

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


Effect of drought on wetland microbial processes

Drought wetland

Control wetland

Peat sample

Peat sample

River


Activity measurements on peat and biofilm samples
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


Ets activity

Control

Drought-simulated

Activity

85% higher

74%

Wetland Biofilm

ETS Activity


Dissolved organic and inorganic nutrients
Dissolved organic and inorganic nutrients

Control

Drought-simulated

26% lower

Concentration

57% higher

Organics Inorganics


Chlorophyll and pha
Chlorophyll and PHA

Control

Drought-simulated

145% higher

Concentration

51% lower

Organics Inorganics


Summary
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


Carbon cycle feedbacks effects of microbial processes on climate change

Carbon cycle feedbacks: effects of microbial processes on climate change

Bardgett et al. 2008. The ISME Journal. 2:805-813


Effect of drought on wetland microbial processes

CO climate change2, CH4, N2O

CO2

?

Corg

Land

CO2

oceans

CaCO3

Carbon cycle feedback


Amounts of greenhouse gases in air
Amounts of greenhouse gases in air climate change

  • 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


Effect of drought on wetland microbial processes

Climate change 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


Role of forests in climate stability
Role of forests in climate stability climate change

  • 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


Effect of drought on wetland microbial processes

0 100 200 300 climate change

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 ( )


Effect of drought on wetland microbial processes

Microbial response to CO climate change2

  • 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


Effect of drought on wetland microbial processes

  • Increase in CO climate change2 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


Summary1
Summary climate change

  • 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)