Microbial carbon recycling: an underestimated process controlling soil carbon dynamics – Part 2: A C3-C4 vegetation change field labelling experiment

[摘要] The mean residence times (MRT) of different compound classes of soil organicmatter (SOM) do not match their inherent recalcitrance to decomposition. Onereason for this is the stabilization within the soil matrix, but recycling,i.e. the reuse of "old" organic material to form new biomass may also playa role as it uncouples the residence times of organic matter from thelifetime of discrete molecules in soil.

We analysed soil sugar dynamics in a natural 30-year old labellingexperiment after a wheat-maize vegetation change to determine the extent ofrecycling and stabilization by assessing differences in turnover dynamicsbetween plant and microbial-derived sugars: while plant-derived sugars areonly affected by stabilization processes, microbial sugars may be subject toboth, stabilization and recycling. To disentangle the dynamics of soilsugars, we separated different density fractions (free particulate organicmatter (fPOM), light occluded particulate organic matter (≤1.6 g cm⁻³; oPOM_1.6), dense occluded particulate organic matter(≤ 2 g cm⁻³; oPOM₂) and mineral-associated organic matter (> 2 g cm⁻³; mineral)) of a silty loam under long-term wheat and maizecultivation. The isotopic signature of neutral sugars was measured by highpressure liquid chromatography coupled to isotope ratio mass spectrometry(HPLC/IRMS), after hydrolysis with 4 M Trifluoroacetic acid.

While apparent MRT of sugars were comparable to totalorganic carbon in the bulk soil and mineral fraction, the apparent MRT ofsugar carbon in the oPOM fractions were considerably lower than those of thetotal carbon of these fractions. This indicates that oPOM formation wasfuelled by microbial activity feeding on new plant input. In the bulk soil,MRT of the mainly plant-derived xylose were significantly lower than thoseof mainly microbial-derived sugars like galactose, rhamnose, fucose,indicating that recycling of organic matter is an important factorregulating organic matter dynamics in soil.

[学科分类] 地球化学与岩石