ARS | Publication request: CONTRIBUTION OF GRASS CROWNS AND SURFACE SOIL ROOTS TO RANGELAND ECOSYSTEM C DYNAMICS

Submitted to: American Society of Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: August 16, 2004
Publication Date: November 1, 2004
Citation: Grant, D.W., Reeder, S.J. 2004. Contribution of grass crowns and surface soil roots to rangeland ecosystem c dynamics. American Society of Agronomy Abstracts. CD Reeder Abstract.

Technical Abstract: The concentration of water soluble organic C (WSOC) in soil provides a measure of C that is readily available for microbial use as well as a measurement of root exudation. However, WSOC is spatially and temporally variable in soil. Root exudates of WSOC tend to be concentrated in rhizoplane soil adhering to coarse roots and thus are not included in measurements of WSOC in bulk soil. This study examines the relative contribution of rhizoplane soil to the total soluble C present in surface soils of two native grassland ecosystems, a shortgrass steppe (SGS), and a northern mixed-grass prairie (NMP). Visible roots were removed from field moist soil, and the concentration of WSOC in the root-associated rhizoplane soil was compared to concentration of WSOC in bulk soil. In both ecosystems, concentration of WSOC in rhizoplane soil was one to two orders of magnitude higher than in bulk soil, and concentrations of WSOC in the soil associated with grass crowns was about 4-fold higher than in the bulk soil. Rhizoplane soil accounted for 28% (NMP) and 16% (SGS) of total WSOC present in the 0-10 cm depth. The concentration of WSOC per unit root mass was higher in rhizoplane soil of the NMP than in the SGS, suggesting inherent differences in the dominant grass species of the two ecosystems in root exudation of labile C. These results emphasize the importance of including rhizoplane WSOC in estimates of soluble organic C in the soil.