Determination of the fate of super(13)C labelled maize and wheat rhizodeposit-C in two agricultural soils in a greenhouse experiment under super(13)C-CO sub(2)-enriched atmosphere

• Published in: Soil biology & biochemistry Vol. 39; no. 12; pp. 3043 - 3055
• Main Authors: Marx, Marc, Buegger, Franz, Gattinger, Andreas, Marschner, Bernd, Zsolnay, Adam, Munch, Jean Charles
• Format: Journal Article
• Language: English
• Published: 01.12.2007
• Subjects: Triticum aestivum; Zea mays
• ISSN: 0038-0717
• DOI: 10.1016/j.soilbio.2007.06.016

A deeper understanding of the contribution of carbon (C) released by plant roots (rhizodeposition) to soil organic matter (SOM) can help to increase our knowledge of global C-cycling. These insights can eventually lead to sustainable management of SOM especially in agricultural systems. This study was conducted to determine the fate of super(13)C labelled rhizodeposit-C of maize and wheat plants. They were grown in a greenhouse in permeable nylon bags filled with upper soil material from two agricultural soils of the same location, but with different crop yields. The bags were placed into pots, which were also filled with soil surrounding the bags. Soil inside the bags was considered as rhizosphere soil, wheras the one outside the bags represented bulk soil. The contributions of rhizodeposits to water extractable organic carbon (WEOC), microbial biomass-C (MB-C), CO sub(2)-C evolution, and total organic carbon (C sub(org)) were investigated during a 7- week growing period. The WEOC, MB-C, CO sub(2)-C, C sub(org) contents and the respective delta super(13)C values were determined regularly, and a newly developed method for determining delta super(13)C values in soil extracts was applied. In both soils, regardless of crop yield potential, significant incorporation of rhizodeposition-derived C was observed in the MB-C, CO sub(2)- C, and C sub(org) pool, but not in the WEOC. The pattern of C incorporation into the different pools was the same for both soils with both plants, and rhizodeposit-derived C was recovered in the order MB-C<C sub(org)<CO sub(2)-C. This showed that rhizodeposits were mainly respired, but since C sub(org) was the second largest pool of the overall balances, they were also stabilized in the soils at least in the short term. It is suggested that the increased SOM mineralization observed in this study (positive priming effects) was probably induced by C exchange processes between the soil matrix and soluble rhizodeposits. Moreover, soluble rhizodeposit-C was detected in MB-C and CO sub(2)-C evolved outside the direct root zone, showing the availability of these C-components in the bulk soil.