The dynamics of neutral sugars in the rhizosphere of wheat. An approach by13C pulse-labelling and GC/C/IRMS

• Published in: Plant and soil 2004-12, Vol.267 (1-2), p.243-253
• Main Authors: Derrien, D., Marol, C., Balesdent, J.
• Format: Article
• Language: English
• Subjects: Carbohydrates; Carbon; Carbon cycle; Gas chromatography; Mass spectrometry; Organic carbon; Organic matter; Polymers; Rhizosphere; Roots; Seedlings; Soil organic matter; Soils; Sugar; Wheat
• ISSN: 0032-079X; 1573-5036
• DOI: 10.1007/s11104-005-5348-8

Rhizodeposition, i.e. the release of carbon into the soil by growing roots, is an important part of the terrestrial carbon cycle. However thein situ nature and dynamics of root-derived carbon in the soil are still poorly understood. Here we made an investigation of the latter in laboratory experiments using^sup 13^CO^sub 2^ pulse chase labelling of wheat (Triticum aestivum L.). We analyzed the kinetics of^sup 13^C-labelled carbon and more specially^sup 13^C carbohydrates in the rhizosphere. Wheat seedlings-soil mesocosms were exposed to^sup 13^CO^sub 2^ for 5 hours in controlled chambers and sampled repeatedly during two weeks for^sup 13^C/C analysis of organic carbon. After a two-step separation of the soil from the roots, the amount of total organic^sup 13^C was determined by isotope ratio mass spectrometry as well as the amounts of^sup 13^C in arabinose, fructose, fucose, glucose, galactose, mannose, rhamnose and xylose. The amount and isotopic ratio of monosaccharides were obtained by capillary gas chromatography coupled with isotope ratio mass spectrometry (GC/C/IRMS) after trimethyl-silyl derivatization. Two fractions were analyzed : total (hydrolysable) and soluble monomeric (water extractable) soil sugars. The amount of organic^sup 13^C found in the soil, expressed as a percentage of the total photosynthetically fixed^sup 13^C at the end of the labelling period, reached 16% in the day following labelling and stabilised at 9% after one week. We concluded that glucose under the form of polymers was the dominant moietie of rhizodeposits. Soluble glucose and fructose were also present. But after 2 days, these soluble sugars had disappeared. Forty percent of the root-derived carbon was in the form of neutral sugars, and exhibited a time-increasing signature of microbial sugars. The composition of rhizospheric sugars rapidly tended towards that of bulk soil organic matter.[PUBLICATION ABSTRACT]