Linking Microbial Community Dynamics Associated with Rhizosphere Carbon Flow in a Biofuel Crop (Jatropha curcas L.)

Photosynthetically derived rhizodeposits are an important source of carbon (C) for microbes in root vicinity and can influence the microbial community dynamics. Pulse labeling of carbon dioxide ((CO2)-C-13) coupled with stable isotope probing techniques have potential to track recently fixed photosynthate into rhizosphere microbial taxa. Therefore, the present investigation assessed the microbial community change associated with the rhizosphere and bulk soil in Jatropha curcas L. (a biofuel crop) by combining phospholipid fatty acid (C-13-PLFA) profiling using a stable isotope (CO2)-C-13 labeling approach. The labeling (C-13) took place after 45 days of germination, PLFAs were extracted from both soils (rhizosphere and bulk) after 1 and 20 days pulse labeling and analyzed by gas chromatography-isotope ratio mass spectrometry. There was no significant temporal effect on the PLFA profiles in the bulk soil, but significantly increased abundance of Gram positive (i15:0) and Gram negative (16:1 omega 7c and 16:1 omega 5c) biomarkers was observed in the rhizosphere soil from day 1 to day 20 after labeling. The Gram negative (16:1 omega 7c) decreased and fungal (18:2 omega 6,9c) increased significantly in rhizospheric soil compared to bulk soil after day 1 of labeling. Whereas, after 20 days of labeling, the Gram negative biomarker (16:1 omega 7c and 18:1 omega 7c) decreased and Gram positive (a15:0) increased significantly in rhizospheric soil compared to bulk soil. One day following labeling, i15:0, a15:0, i16:0, 16:1.5c, 16:0, i17:0, a17:0, 18:2.6,9c, 18:1.9c, and 18:0 PLFAs were significantly more enriched in delta C-13 in the rhizosphere than in the bulk soil. Twenty days after labeling, 16:1 omega 5c (Gram negative) and 18:2 omega 6,9c (fungal) were significantly more enriched in delta C-13 in the rhizosphere than in the bulk soil. These results shows the effectives of PLFA coupled using the pulse chase labeling technique to examine the microbial community changes in response to recently fixed photosynthetic C flow in rhizodeposits.