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.