Calderón, F. J., D. J. Schultz, and E. A. Paul. 2012. Carbon allocation, belowground transfers, and lipid turnover in a plant–microbial association. Soil Science Society of America Journal 76:1614-1623.
Radioactive tracers were used to study the C allocation to coarse and fine roots, aboveground plant tissues, mycorrhizal lipids, belowground respiration, and soil in a mycorrhizal association. Sorghum bicolor (L.) Moench was grown in soil with a nonmycorrhizal microbial inoculum with and without Glomus clarum, a mycorrhizal inoculant. Fifty-one-day-old mycorrhizal (M) and nonmycorrhizal (NM) plants were subjected to a 3-h exposure to 14CO2 and sequentially harvested after 52, 54, 57, 64, and 76 d. Mycorrhizal plants assimilated 21% more 14C than NM plants, even though they were slightly smaller in size. They also had a higher percentage and absolute allocation of 14C to root tissue, belowground respiration, and soil. Mycorrhizal roots had a higher content of total lipids and total fatty acids. The fungal fatty acid 16:1ω5, usually associated with arbuscular mycorrhizal fungi, comprised up to 29.5% of the total fatty acid content of M roots, while NM roots had only trace levels of this molecule. Thin-layer chromatography was used to separate the fatty acids extracted from the roots. The 14C of the various components was determined by radiography. The 14C mean residence time (MRT) of the mycorrhizal fatty acid 16:1ω5 was calculated at 7.1 d. The monoenoic, saturated, and total fatty acids had MRTs ranging from 11.1 to 14.3 d. The lipids of NM roots incorporated less 14C label. This underscores the difference in the lipid C cycle between the M and NM roots. Translocation of the 14C to soil was 6.3% of the photosynthesized C in the M plants relative to only 2.4% in the NM plants, giving an indication of its movement into the mycorrhizal hyphae as well as to the soil.
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