September 30, 2005 ICDC7 Boulder, Colorado 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 Institute of Agroecology (FAL), Braunschweig, Germany

September 30, 2005 ICDC7 Boulder, ColoradoOverview  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

September 30, 2005 ICDC7 Boulder, Colorado 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 CO 2 flux from soil to atmosphere in response to proposed increase of C input to soil in elevated CO 2 world  Contradictory effect of elevated CO 2 on soil microbial biomass: some studies show positive response and some show no response or even negative

September 30, 2005 ICDC7 Boulder, Colorado 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

September 30, 2005 ICDC7 Boulder, Colorado  to study the effect of elevated concentration of atmospheric CO 2 on biomass and specific growth rates of microbial communities of soil and rhizosphere Aim Hypotheses  Elevated CO 2 effects growth characteristics of soil and rhizosphere microbial communities

September 30, 2005 ICDC7 Boulder, Colorado  Introduction  Experimental design and methods  Biomass measured by SIR and dsDNA  Kinetic characteristics of substrate- induced growth response on glucose  Discussion and conclusions

September 30, 2005 ICDC7 Boulder, Colorado Biosphere 2 Center, Arizona, USA  ambient (400 ppm) and elevated (800 or 1200 ppm) atmospheric CO 2 concentrations  Cottonwood tree (Populus deltoides)

September 30, 2005 ICDC7 Boulder, Colorado Free Air Carbon Dioxide Enrichment (FACE) Braunschweig, Germany  ambient ( ppm) and elevated (550 ppm) atmospheric CO 2 concentrations  N fertilization at rates 126 and 63 kg·ha -1 ·year -1  Sampling: sugar beet, 2002 and 2005 – winter wheat 2002 and 2005 – winter wheat

September 30, 2005 ICDC7 Boulder, Colorado 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)

September 30, 2005 ICDC7 Boulder, Colorado Basic principle of SIGR method ( Panikov et al., 1991) CO 2 evolution rate after substrate amendment ( ): v(t) = A + B * exp( m *t), where 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

September 30, 2005 ICDC7 Boulder, Colorado Calculation of active and total microbial biomass based on SIGR  Active microbial biomass: X’ = B /  m  Total microbial biomass: X = X’ * r 0, where r 0 – activity status calculated from the ratio between A and B

September 30, 2005 ICDC7 Boulder, Colorado  Introduction  Experimental design and methods  Biomass measured by SIR and dsDNA  Kinetic characteristics of substrate- induced growth response on glucose  Discussion and conclusions

September 30, 2005 ICDC7 Boulder, Colorado Soil microbial biomass in intensive agroforestry biome of Biosphere 2 Center Please, see also poster HI-396 by Kudeyarov et al.

September 30, 2005 ICDC7 Boulder, Colorado  Rhizosphere effect on microbial biomass (SIR) and dsDNA in soil under sugar beets grown at different atmospheric CO 2 concentrations  Increase in microbial biomass (SIR) under elevated CO 2 was only transient and was not supported by data on dsDNA content

September 30, 2005 ICDC7 Boulder, Colorado  Introduction  Experimental design and methods  Biomass measured by SIR and dsDNA  Kinetic characteristics of substrate- induced growth response on glucose  Discussion and conclusions

September 30, 2005 ICDC7 Boulder, Colorado Atmospheric CO 2 effect on SIGR: soil under cottonwood tree (Populus deltoides) CO 2 conc.  max 400ppm0.30 ± ppm0.39 ± ppm0.47 ± 0.06

September 30, 2005 ICDC7 Boulder, Colorado Atmospheric CO 2 effect on SIGR: soil under sugar beets Elevated CO 2 Ambient CO 2

September 30, 2005 ICDC7 Boulder, Colorado Atmospheric CO 2 effect on SIGR: soil under winter wheat Elevated CO 2 Ambient CO 2

September 30, 2005 ICDC7 Boulder, Colorado Atmospheric CO 2 effect on SIGR: soil under winter wheat Elevated CO 2 Ambient CO 2

September 30, 2005 ICDC7 Boulder, Colorado 3-way ANOVA, Soil under sugar beets, Contribution of independent factors: elevated CO 2, 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

September 30, 2005 ICDC7 Boulder, Colorado 3-way ANOVA, Soil under winter wheat, Contribution of independent factors: elevated CO 2, 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

September 30, 2005 ICDC7 Boulder, Colorado Effect of CO 2 enrichment on microbial turnover in soil Exudation Humification CO 2 Respiration Shift to r-strategy Human activities Photosynthesis

September 30, 2005 ICDC7 Boulder, Colorado Critical question for warming potential acceleration / mitigation  How will change the ratio respiration/humification after changing of atmospheric CO 2 concentration ? Further studies combining kinetic approach with C and N labeling are needed

September 30, 2005 ICDC7 Boulder, Colorado Conclusions  Elevated CO 2 affects the functional structure of soil microbial community  The size of active/total soil microbial biomass depends on elevated CO 2 in a lesser extent  Specific growth rate (µ m ) – the most sensitive parameter reflecting changes in ecological strategy of microbial communities

September 30, 2005 ICDC7 Boulder, Colorado Thank you for attention! ACKNOWLEDGEMENTS Research was supported by BMVEL, DAAD and Russian Foundation for Basic ResearchResearch 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 conferenceSponsorship of ICDC7 supporting agencies and decision of Scientific Committee enabled participation of first author in conference Special thanks to Karl Bil’ - Biosphere 2 CenterSpecial thanks to Karl Bil’ - Biosphere 2 Center