Bacteria and fungi respond differently to multifactorial climate change in a temperate heathland, traced with ¹³C-Glycine and FACE CO₂

It is vital to understand responses of soil microorganisms to predicted climate changes, as these directly control soil carbon (C) dynamics. The rate of turnover of soil organic carbon is mediated by soil microorganisms whose activity may be affected by climate change. After one year of multifactorial climate change treatments, at an undisturbed temperate heathland, soil microbial community dynamics were investigated by injection of a very small concentration (5.12 µg C g(-1) soil) of (13)C-labeled glycine ((13)C2, 99 atom %) to soils in situ. Plots were treated with elevated temperature (+1°C, T), summer drought (D) and elevated atmospheric carbon dioxide (510 ppm [CO2]), as well as combined treatments (TD, TCO2, DCO2 and TDCO2). The (13)C enrichment of respired CO2 and of phospholipid fatty acids (PLFAs) was determined after 24 h. (13)C-glycine incorporation into the biomarker PLFAs for specific microbial groups (Gram positive bacteria, Gram negative bacteria, actinobacteria and fungi) was quantified using gas chromatography-combustion-stable isotope ratio mass spectrometry (GC-C-IRMS). Gram positive bacteria opportunistically utilized the freshly added glycine substrate, i.e. incorporated (13)C in all treatments, whereas fungi had minor or no glycine derived (13)C-enrichment, hence slowly reacting to a new substrate. The effects of elevated CO2 did suggest increased direct incorporation of glycine in microbial biomass, in particular in G(+) bacteria, in an ecosystem subjected to elevated CO2. Warming decreased the concentration of PLFAs in general. The FACE CO2 was (13)C-depleted (δ(13)C = 12.2‰) compared to ambient (δ(13)C = ∼-8‰), and this enabled observation of the integrated longer term responses of soil microorganisms to the FACE over one year. All together, the bacterial (and not fungal) utilization of glycine indicates substrate preference and resource partitioning in the microbial community, and therefore suggests a diversified response pattern to future changes in substrate availability and climatic factors

Bacteria and Fungi Respond Differently to Multifactorial Climate Change in a Temperate Heathland, Traced with 13C-Glycine and FACE CO2

It is vital to understand responses of soil microorganisms to predicted climate changes, as these directly control soil carbon (C) dynamics. The rate of turnover of soil organic carbon is mediated by soil microorganisms whose activity may be affected by climate change. After one year of multifactorial climate change treatments, at an undisturbed temperate heathland, soil microbial community dynamics were investigated by injection of a very small concentration (5.12 µg C g−1 soil) of 13C-labeled glycine (13C2, 99 atom %) to soils in situ. Plots were treated with elevated temperature (+1°C, T), summer drought (D) and elevated atmospheric carbon dioxide (510 ppm [CO2]), as well as combined treatments (TD, TCO2, DCO2 and TDCO2). The 13C enrichment of respired CO2 and of phospholipid fatty acids (PLFAs) was determined after 24 h. 13C-glycine incorporation into the biomarker PLFAs for specific microbial groups (Gram positive bacteria, Gram negative bacteria, actinobacteria and fungi) was quantified using gas chromatography-combustion-stable isotope ratio mass spectrometry (GC-C-IRMS).Gram positive bacteria opportunistically utilized the freshly added glycine substrate, i.e. incorporated 13C in all treatments, whereas fungi had minor or no glycine derived 13C-enrichment, hence slowly reacting to a new substrate. The effects of elevated CO2 did suggest increased direct incorporation of glycine in microbial biomass, in particular in G+ bacteria, in an ecosystem subjected to elevated CO2. Warming decreased the concentration of PLFAs in general. The FACE CO2 was 13C-depleted (δ13C = 12.2‰) compared to ambient (δ13C = ~−8‰), and this enabled observation of the integrated longer term responses of soil microorganisms to the FACE over one year. All together, the bacterial (and not fungal) utilization of glycine indicates substrate preference and resource partitioning in the microbial community, and therefore suggests a diversified response pattern to future changes in substrate availability and climatic factors

¹³C enrichment (atom%) in individual PLFAs.

<p>Gram positive biomarker <i>i</i>17:0 (<b>A</b>), the non-specific PLFA 16:0 (<b>B</b>), the non-specific 18:0 (<b>C</b>) and the fungi biomarker PLFA 18:2ω6,9 (<b>D</b>) one day after addition of ¹³C₂-glycine to field plots subjected to <i>in situ</i> treatment through one year with the climate change factors: elevated atmospheric CO₂ concentration (CO2), summer drought (D) and warming (T), and those treatments in all combinations. A is ambient control = no treatment. Error bars represent standard error. Significant effects of treatments: * is P<0.05.</p

¹³C-CO₂ enrichment in soil air (atom %).

<p>A time-series beginning a few hours prior to addition of the ¹³C-enriched glycine label till 168 hours after addition fit a log-normal curve: ¹³C-CO₂ = 1.108+1.359*exp(−0.5*(ln(T/3.269)/1.797)²)/T); (R² = 0.8832). Curve indicates average, 95% Confidence Band and 95% Prediction Band.</p

Concentration (µg PLFA·g⁻¹ SOM) in top soil of PLFAs.

<p>Sum of all bacterial and fungal PLFA biomarkers (<b>A</b>); the fungal PLFA biomarker 18:2ω6,9 (<b>B</b>); all gram positive biomarkers (<b>C</b>) and all bacteria PLFA biomarkers (<b>D</b>); one day after addition of glycine to field plots subjected to <i>in situ</i> treatment through one year with the climate change factors: elevated atmospheric CO₂ concentration (CO2), summer drought (D) and warming (T), and those treatments in all combinations. A is ambient control = no treatment. Error bars represent standard error. Significant effects of treatments: * is P<0.05.</p

Significant effect of climate change treatments (P-values) on PLFA ¹³C enrichment from soils from the CLIMAITE experiment sampled in August 2007.

<p>Soil was sampled one day after addition of ¹³C₂-glycine to field plots subjected to <i>in situ</i> treatment through one year with the climate change factors: elevated atmospheric CO₂ concentration (CO2) summer drought (D) and warming (T), and those treatments in all combinations. Linear mixed models (proc mixed and GLM in SAS) with main effects: CO₂, temperature (T) and drought (D) and interactions between the factors CO₂, T and D.</p