Measurement of rhizosphere respiration and organic matter decomposition using natural 13C

Abstract

Due to the limitations in methodology it has been a difficult task to measure rhizosphere respiration and original soil carbon decomposition under the influence of living roots. 14C-labeling has been widely used for this purpose in spite of numerous problems associated with the labeling method. In this paper, a natural 13C method was used to measure rhizosphere respiration and original soil carbon decomposition in a short-term growth chamber experiment. The main objective of the experiment was to validate a key assumption of this method: the 6~3C value of the roots represents the 613C value of the rhizosphere respired CO2. Results from plants grown in inoculated carbon-free medium indicated that this assumption was valid. This natural ~3C method was demonstrated to be advantageous for studying rhizosphere respiration and the effects of living roots on original soil carbon decomposition.

Growth, nutrition, and soil respiration of a mycorrhiza-defective tomato mutant and its mycorrhizal wild-type progenitor

“…Plant-derived C enters the soil as plant litter and root exudates (Coleman et al 1976;Butler et al 2003), and is released as CO 2 by the respiration of roots and soil microorganisms. As much as 50% of soil CO 2 efflux is rootderived (Rochette and Angers 1999;Kuzyakov and Domanski 2002), with contributions coming directly from root respiration and indirectly from heterotrophic respiration of C originating as root exudates, exfoliates (sloughed cells and root hairs), and root debris (Ingham et al 1985;Cheng 1996;Luo et al 1996;Kuzyakov and Domanski 2002;Langley et al 2005). Roots may also alter soil respiration via inorganic carbon fixation in the root zone (Cramer et al 1993).…”

Below-ground partitioning (14C) and isotopic fractionation (δ13C) of carbon recently assimilated by maize

“…The δ 13 C of CO 2 was significantly depleted by 0.7 ‰ compared with the roots in the NS treatment. This suggests that earlier obtained results of the absence of 13 C fractionation by root respiration [17,21,44] must be used with caution, because fractionation can be affected by nutrient status. The other two treatments showed no fractionation between roots and respired CO 2 .…”

“…As an alternative, 13 C natural abundance has been frequently used in the last 15 years for estimation of below-ground C input and its partitioning [3,[14][15][16][17][18][19]. 13 C natural abundance has some advantages towards artificial labelling, e.g.…”

“…Nevertheless, the results of any C balance obtained by 13 C natural abundance would be biased if any isotopic fractionation did occur by rhizodeposition and root respiration [20]. However, some studies have shown that there is no difference in δ 13 C values of roots and of root respiration for winter wheat [17] and for bean and maize [21]. In incubation experiments, it was observed that CO 2 respired by microbial decomposition of roots was depleted by 1-10 ‰ [22][23][24].…”

Carbon Fluxes in the Rhizosphere

“…A recent variation on the continuous labeling studies is the natural abundance method (e.g., Cheng 1996;Hanson et al 2000), which uses naturally occurring isotopic composition differences to separate root-from soil-derived materials, and allows development of belowground carbon budgets without the expensive and difficult experimental setups, and does not require separation from the ambient atmosphere. However, several researchers have pointed out that this is a noisy system (Killham and Yeomans 2001), and therefore only large differences between treatments can be distinguished.…”