Dynamics of soil organic matter turnover and soil respired CO₂ in a temperate grassland labelled with ¹³C

• Published in: European journal of soil science Vol. 58; no. 6; pp. 1364 - 1372
• Main Authors: Theis, D.E, Jaeggi, M, Aeschlimann, D, Blum, H, Frossard, E, Siegwolf, R.T.W
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.12.2007; Blackwell Publishing Ltd; Blackwell Science
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Soil science; Soils; Surficial geology; Soil science; Earth science
• ISSN: 1351-0754; 1365-2389
• DOI: 10.1111/j.1365-2389.2007.00941.x

The fate of carbon (C) in grassland soils is of particular interest since the vast majority in grassland ecosystems is stored below ground and respiratory C-release from soils is a major component of the global C balance. The use of ¹³C-depleted CO₂ in a 10-year free-air carbon dioxide enrichment (FACE) experiment, gave a unique opportunity to study the turnover of the C sequestered during this experiment. Soil organic matter (SOM), soil air and plant material were analysed for δ¹³C and C contents in the last year of the FACE experiment (2002) and in the two following growing seasons. After 10 years of exposure to CO₂ enrichment at 600 ppmv, no significant differences in SOM C content could be detected between fumigated and non-fumigated plots. A ¹³C depletion of 3.4[per thousand] was found in SOM (0-12 cm) of the fumigated soils in comparison with the control soils and a rapid decrease of this difference was observed after the end of fumigation. Within 2 years, 49% of the C in this SOM (0-12 cm) was exchanged with fresh C, with the limitation that this exchange cannot be further dissected into respiratory decay of old C and freshly sequestered new C. By analysing the mechanistic effects of a drought on the plant-soil system it was shown that rhizosphere respiration is the dominant factor in soil respiration. Consideration of ecophysiological factors that drive plant activity is therefore important when soil respiration is to be investigated or modelled.