Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2012
Publication Date: 7/18/2012
Citation: Calderon, F.J., Schultz, D.J., Eldor, P.A. 2012. Carbon allocation below ground transfers and lipid turnover in a plant-microbial association. Soil Science Society of America Journal. 76:1614-1623. Interpretive Summary: The mycorrhizal association is a normal occurring, important factor in the retention or loss of C in terrestrial ecosystems as well as in plant nutrition. In this study we show how the balance between above and below ground plant productivity is profoundly affected by this soil fungus, which is a normal occurrence in dryland crops. We found that the presence of the fungus decreased the growth of Sorghum, mainly because more of the C from photosynthesis was transferred to soil and soil CO2. We also show that lipids play an important role in the carbon cycle of mycorrhizal fungi, and thanks to the use of radioactive tracers, were able to measure the half life of C in this important constituent.
Technical Abstract: Radioactive tracers were used to study the carbon allocation to above ground, coarse- and fine-roots, plant tissues, mycorrhizal lipids, below-ground respiration, and to soil in a mycorrhizal association. Sorghum bicolor was grown in soil with a non mycorrhizal microbial inoculum with and without Glomus clarum. Fifty-one d old mycorrhizal (M) and non-mycorrhizal (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 of slightly smaller size. They also had a higher percentage and absolute allocation of 14C to root tissue, below-ground respiration, and soil. Mycorrhizal plants had a higher content of total lipids and total fatty acids. The fungal fatty acid 16:1 '5, 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 MRT of the mycorrhizal fatty acid 16:1 '5 was calculated at 7.1d. 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 underscored 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 relative to only 2.4 % in the NM, giving an indication of its movement into the mycorrhizal hyphae.