Elevated CO2 does not favor a fungal decomposition pathway

We examined the effect of prolonged elevated CO₂ on the concentration of fungal- and bacterial-derived compounds by quantifying the soil contents of the amino sugars glucosamine, galactosamine and muramic acid. Soil samples were collected from three different terrestrial ecosystems (grassland, an aspen forest and a soybean/corn agroecosystem) that were exposed to elevated CO₂ under FACE conditions for 3-10 years. Amino sugars were extracted from bulk soil and analyzed by gas chromatography. Elevated CO₂ did not affect the size or composition of the amino sugar pool in any of the systems. However, high rates of fertilizer N applications decreased the amount of fungal-derived residues in the grassland system. We suggest that these results are caused by a decrease in saprophytic fungi following high N additions. Furthermore, our findings imply that the contribution of saprophytic fungi and bacteria to SOM in the studied ecosystems is largely unaffected by elevated CO₂.