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S.А. Blagodatsky , Е.V. Blagodatskaya, E.G. Demyanova, V.N. Kudeyarov

SUBSTRATE INDUCED GROWTH RESPONSE OF SOIL AND RHIZOSPHERE MICROBIAL COMMUNITIES UNDER ELEVATED CO 2. S.А. Blagodatsky , Е.V. Blagodatskaya, E.G. Demyanova, V.N. Kudeyarov Institute of Physicochemical and Biological Problems in Soil Science, Pushchino, Russia Т.-H. Аnderson, H.-J. Weigel

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S.А. Blagodatsky , Е.V. Blagodatskaya, E.G. Demyanova, V.N. Kudeyarov

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  1. SUBSTRATE INDUCED GROWTH RESPONSE OF SOIL AND RHIZOSPHERE MICROBIAL COMMUNITIES UNDER ELEVATED CO2 S.А. Blagodatsky, Е.V. Blagodatskaya, E.G. Demyanova, V.N. Kudeyarov Institute of Physicochemical and Biological Problems in Soil Science, Pushchino, Russia Т.-H. Аnderson, H.-J. Weigel Institute of Agroecology (FAL), Braunschweig, Germany

  2. Overview • Introduction • Experimental design and methods • Soil Microbial Biomass measured by SIR and dsDNA • Kinetic characteristics of substrate-induced growth response on glucose • Discussion and conclusions

  3. Motivation: why it is necessary to study ? • Soil microbial biomass and activity are key factors controlling C-turnover in soil and respectively acceleration/mitigation of the resultant CO2 flux from soil to atmospherein response to proposed increase of C input to soil in elevated CO2 world • Contradictory effect of elevated CO2 on soil microbial biomass: some studies show positive response and some show no response or even negative

  4. What could help: • Accounting for other important factors: soil N level, type of growing plant, soil moisture content, dynamic nature of observed effects, spatial distinction between bare soil and rhizosphere • More careful consideration of functional properties and structure of soil microbial community

  5. Hypotheses Aim • Elevated CO2 effects growth characteristics of soil and rhizosphere microbial communities • to study the effect of elevated concentration of atmospheric CO2 on biomass and specific growth rates of microbial communities of soil and rhizosphere

  6. Biosphere 2 Center, Arizona, USA • ambient (400 ppm) and elevated (800 or 1200 ppm) atmospheric CO2 concentrations • Cottonwood tree (Populus deltoides)

  7. Free Air Carbon Dioxide Enrichment (FACE) Braunschweig, Germany • ambient (350-370 ppm) and elevated (550 ppm) atmospheric CO2 concentrations • N fertilization at rates 126 and 63 kg·ha-1·year-1 • Sampling: 2001 - sugar beet, 2002 and 2005 – winter wheat

  8. Measured characteristics: • Soil microbial biomass – SIR method (Anderson, Domsch, 1978) • Soil dsDNA – direct extraction and measurement of fluorescence after dyeing with Picogreen (Marstorp, Witter, 1999; Blagodatskaya et al., 2004) • Kinetic parameters of substrate-induced growth response of soil microorganisms, total and active microbial biomass by SIGR method– fitting the data on respiration rates measured after soil amendment with glucose + NPK and/or yeast extracts (Panikov et al., 1991; Blagodatsky et al., 2000)

  9. Basic principle of SIGR method (Panikov et al., 1991) CO2 evolution rate after substrate amendment ( ): v(t) = A + B * exp(m*t) , where A – initial rate of uncoupled (non-growth) respiration B – initial rate of coupled (growth) respiration m–Maximal specific growth rate t -time

  10. Calculation of active and total microbial biomass based on SIGR • Active microbial biomass: X’ = B / m • Total microbial biomass: X = X’ * r0, where r0 – activity status calculated from the ratio between A and B

  11. Soil microbial biomass in intensive agroforestry biome of Biosphere 2 Center Please, see also poster HI-396 by Kudeyarov et al.

  12. Rhizosphere effect on microbial biomass (SIR) and dsDNA in soil under sugar beets grown at different atmospheric CO2 concentrations • Increase in microbial biomass (SIR) under elevated CO2 was only transient and was not supported by data on dsDNA content

  13. Atmospheric CO2 effect on SIGR: soil under cottonwood tree (Populus deltoides)

  14. Atmospheric CO2 effect on SIGR: soil under sugar beets Elevated CO2 AmbientCO2

  15. Atmospheric CO2 effect on SIGR: soil under winter wheat - 2002 Elevated CO2 AmbientCO2

  16. Atmospheric CO2 effect on SIGR: soil under winter wheat - 2005 Elevated CO2 AmbientCO2

  17. 3-way ANOVA,Soil under sugar beets,Contribution of independent factors: elevated CO2, rate of N-fertilizers and distance from root surface on total variation of maximal specific growth rate of soil microorganisms, total and active microbial biomass

  18. 3-way ANOVA ,Soil under winter wheat,Contribution of independent factors: elevated CO2, rate of N-fertilizers and distance from root surface on total variation of maximal specific growth rate of soil microorganisms, total and active microbial biomass

  19. Effect of CO2 enrichment on microbial turnover in soil CO2 Human activities Photosynthesis Respiration Humification Exudation Shift to r-strategy

  20. Critical question for warming potential acceleration / mitigation • How will change the ratio respiration/humification after changing of atmospheric CO2 concentration ? Further studies combining kinetic approach with C and N labeling are needed

  21. Conclusions • Elevated CO2 affects the functional structure of soil microbial community • The size of active/total soil microbial biomass depends on elevated CO2 in a lesser extent • Specific growth rate (µm) – the most sensitive parameter reflecting changes in ecological strategy of microbial communities

  22. Thank you for attention! ACKNOWLEDGEMENTS • Research was supported by BMVEL, DAAD and Russian Foundation for Basic Research • Sponsorship of ICDC7 supporting agencies and decision of Scientific Committee enabled participation of first author in conference • Special thanks to Karl Bil’ - Biosphere 2 Center

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