dynamics of neutral sugars in the rhizosphere of wheat. An approach by 13C 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: Acid soils; Agricultural soils; Agronomy. Soil science and plant productions; Biochemistry; Biochemistry and biology; Biological and medical sciences; Carbon; Chemical, physicochemical, biochemical and biological properties; Fundamental and applied biological sciences. Psychology; gas chromatography; General agronomy. Plant production; isotope labeling; mass spectrometry; nutrient transport; Organic soils; Physics, chemistry, biochemistry and biology of agricultural and forest soils; plant nutrition; Plants; Rhizosphere; Soil biochemistry; Soil organic carbon; Soil organic matter; Soil science; soil-plant interactions; Soil-plant relationships. Soil fertility; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Sugars; Triticum aestivum; wheat
• ISSN: 0032-079X; 1573-5036

Rhizodeposition, i.e. the release of carbon into the soil by growing roots, is an important part of the terrestrial carbon cycle. However the in 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 ¹³CO₂ pulse chase labelling of wheat (Triticum aestivum L.). We analyzed the kinetics of ¹³C-labelled carbon and more specially ¹³C carbohydrates in the rhizosphere. Wheat seedlings-soil mesocosms were exposed to ¹³CO₂ for 5 hours in controlled chambers and sampled repeatedly during two weeks for ¹³C/C analysis of organic carbon. After a two-step separation of the soil from the roots, the amount of total organic ¹³C was determined by isotope ratio mass spectrometry as well as the amounts of ¹³C in arabinose, fructose, fucose, glucose, galactose, mannose, rhamnose and xylose. The amount and isotopie 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 ¹³C found in the soil, expressed as a percentage of the total photosynthetically fixed ¹³C 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.