Molecular structures as drivers and tracers of terrestrial C fluxes - An ESF Network

 

 

 

The story of carbon stabilization in soils is one of complex molecular transformations. However, up to now, the wealth of information on carbon cycling contained in the chemical structure of the soil organic matter remained little exploited for lack of appropriate methodology. This is now changing rapidly due to the development of environmental isotopic and organic chemistry techniques. Examples of these techniques are 13C and 15N nuclear magnetic resonance, chemolyse and multiple pyrolysis systems associated with gas chromatography and compound specific isotope ratio mass spectrometry (IRMS), as well as thermal analyses coupled to mass spectrometers (MS) and IRMS.

MOLTER focuses on five major research topics in order to stimulate and develop the knowledge on natural molecular structures and their role as drivers and tracers of terrestrial C fluxes:

  1. Molecular composition and turnover of soil organic matter
  2. Plant molecular structures as drivers of C stabilisation in soils
  3. Fire transformations of plant and soil molecular structures
  4. Molecular markers in soils
  5. Dissolved organic molecules in soils: origin, functionality and transport

The running period of the ESF MOLTER Research Networking Programme is for five years from March 2008 to February 2013.

 

 

 

About

Soil organic matter (SOM) represents the largest terrestrial carbon (C) reservoir. This C is stored in the form of a highly complex mixture of organic molecules. A wide range of plant molecules enter the soil system, from soluble amino-acids to structural lignin polymers, from labile starch to recalcitrant tannin structures, from hydrophilic sugars to hydrophobic alkanes. Depending on their properties, such as size, structure and functional group content, as well as soil and climatic conditions, these molecular structures undergo (i) abiotic reactions, (ii) are directly adsorbed on mineral surfaces, or (iii) assimilated by soil microbes. New chemical structures are produced such as microbial amino-sugars and phospholipid fatty acids.

The molecular nature of these various compounds is therefore a determining factor for C stabilisation in soils. Certain compounds might be strongly adsorbed on soil mineral surfaces and become directly stabilized. Other compounds will be quickly assimilated by the microbial biomass. The growth yield efficiency of soil microbes, i.e. their ability to maximize C assimilation vs. CO2 losses, also depends on the molecular structure of the assimilated compounds. Multiple non-biotic reactions can further alter the molecular composition of soil organic matter. 

Molecular tracers are records of the origin and history of chemical transformations of soil organic compounds. Small variations in the chemical composition of plant molecules can yield important clues about the plant species and organs they originate from. The 13C isotopic signature of plant molecular families is characteristic of the type of photosynthetic pathway used by the vegetation. In soils under vegetation-type transitions, the resulting isotopic contrast at the molecular level provides us with a powerful tool to investigate the turnover rate of these compounds in the soil environment. Microbial activities affecting these compounds can also be traced with molecular methods. The alteration degree of certain molecules tells us about the environment in which they have evolved. MOLTER promotes the investigation of the molecular mechanisms controlling carbon fluxes in terrestrial ecosystems.