Dr Ton Gorissen¹

¹IsoLife, Wageningen, Netherlands

Stable isotopes like 13C have been used in ecology for decades in tracer studies of plant materials in organic environments like natural soils. They are used to study distribution of recently added organic matter amongst SOM fractions, fluxes of C and N between SOM pools, or to unravel biodiversity and food web interactions in complex soil ecosystems.

The stable-isotope labelled plant materials that IsoLife produces have been used in many papers describing the dynamics of SOM. These materials opened up new ways in i) decomposition studies, ii) stable isotope probing studies on trophic interactions and functional relationships in soil ecosystems, and iii) the sensitivity of detection techniques.

1. i) Decomposition studies have been carried out with uniformly 13C-labelled plant parts or extracted plant materials like lignin or cellulose yielding detailed information about fractions respired, distribution among SOM pools, and SOM transformation. Issues on decomposition efficiency, substrate availability, priming, stabilisation of SOM, and microbial utilisation can be better studied, providing useful data for e.g. carbon sequestration related to climate change.
2. ii) Stable Isotope Probing enables the detection of functional organisms in complex ecosystems at species level using U-13C substrates and density gradient centrifugation to separate 12C- from 13C-DNA or -RNA. Subsequent sequencing of the 13C-bands reveals the active, functional species. Community structure, biodiversity, and symbiotic associations have been studied with a renewed focus.

iii) Methods for tracing C and nutrient transfer between hosts and organisms can be measured in situ using continuous 13C-labelling at extreme enrichment levels (>97 atom %) or visualised by direct imaging using microscopy techniques such as NanoSIMS or FISH.

During the last few years, many papers have been published based on the use of uniformly 13C-labelled plant materials (https://isolife.nl/publications/). The poster shows an overview of the achievements during the last 3 years of using U-13C-labelled substrates in SOM-studies.