BayCEER Workshop 2019

Micro-scale mapping techniques for carbon detection and quantification in soil rhizosphere

P 2.3 in Stable isotopes in environmental research - bridging disciplines, organisms and processes

Dispersal of rhizodeposits in soil may significantly affect carbon (C) storage. Due to the lack of techniques which can analyze C dispersal in an undisturbed environment, it was not clear to which extent the arrangement of roots, pores and solid soil matter control C dispersal, turnover and storage. An integrated approach based on soil hyperspectral reflectance method and laser ablation stable isotope ratio mass spectrometry (LA-IRMS), was developed to provide spatially distributed data of pulse-derived ¹³C tracers from roots towards soil rhizosphere environment. LA-IRMS enabled us more detailed and in situ analyses of C gradients and hotspots of OM accumulation, e.g. in pores with a resolution of 15 to 20 μm. To do so we coupled a 213 nm laser with a modified PreCon combustion interface, a GC column and an isotope ratio mass spectrometer. Laser shots were performed in a gradient of 6 shots from the root surface towards bulk soil, with more narrow distances to the root. The laser shots were spatially referenced with hyperspectral pictures and computer tomographic, enabling the superposition of C contents, its isotopic composition and the relationship to pore space in soil. Two maize genotypes with significantly different root morphology were used as model plants. Soils with different texture (silt loam and loamy sand) were used to evaluate the influence of soil inorganic matter and pore volume on C gradients. We found out a way to describe the development and testing of combine methodologies on soil thin sections (diameter 16 mm, height 3 mm) and determined:  1. The fate of carbon root exudates and recognize where in the rhizosphere are hotspots of carbon input into soil located; 2. Which soil volume around the root is influenced by root- and microorganism-derived deposits, and its relevance with carbon storage or loss; 3. To what extent do these findings depend on self-organization (root age) or external factors like plant genotype with different root hair development.

 

Keywords: hyper spectral imaging, laser ablation, root, exudates, computer tomography.