Microbial carbon recycling – an underestimated process controlling soil carbon dynamics – Part 1: A long-term laboratory incubation experiment

[摘要] Independent of its chemical structure carbon (C) persists in soil forseveral decades, controlled by stabilization and recycling. To disentanglethe importance of the two factors on the turnover dynamics of soil sugars,an important compound of soil organic matter (SOM), a 3-year incubationexperiment was conducted on a silty loam soil under different types of landuse (arable land, grassland and forest) by adding ¹³C-labelled glucose.The compound-specific isotope analysis of soil sugars was used to examinethe dynamics of different sugars during incubation.

Sugar dynamics were dominated by a pool of high mean residence times (MRT)indicating that recycling plays an important role for sugars. However, thiswas not substantially affected by soil C content. Six months after labeladdition the contribution of the label was much higher for microbial biomassthan for CO₂ production for all examined land use types, corroboratingthat substrate recycling was very effective within the microbial biomass.Two different patterns of tracer dynamics could be identified for differentsugars: while fucose and mannose showed highest label contribution at thebeginning of the incubation with a subsequent slow decline, galactose andrhamnose were characterized by slow label incorporation with subsequentlyconstant levels, which indicates that recycling is dominating the dynamicsof these sugars. This may correspond to (a) different microbial growingstrategies (r and K-strategist) or (b) location within or outside the cellmembrane (lipopolysaccharides vs. exopolysaccharides) and thus be subject ofdifferent re-use within the microbial food web. Our results show how themicrobial community recycles substrate very effectively and that high lossesof substrate only occur during initial stages after substrate addition. Thisstudy indicates that recycling is one of the major processes explaining thehigh MRT observed for many SOM fractions and thus is crucial forunderstanding the global soil C cycle.

[学科分类] 地球化学与岩石