Carbon dioxide (CO2) released from soil ecosystems is a function of the central carbon (C) metabolic network; which includes glycolysis, the TCA cycle, and the pentose phosphate pathway (PPP). We typically find that glucose in soils is processed via the PPP, more so than via glycolysis. For the first time, however, we found a different metabolic pattern in a tidal freshwater marsh and a mixed conifer mineral soil. Metabolic flux analysis, a method used in soil to probe the activity of the various pathways of the central C metabolic network, was used in this study. We added six position-specific 13C-labeled glucose isotopomers to the soil, traced 13CO2 release over 60 minutes (mineral soil) and 90 minutes (marsh sediment) with aerobic and anaerobic headspace conditions. We also measured bacterial community composition. We hypothesized that 1) soil and sediment exhibit high PPP activity under aerobic and anaerobic conditions; 2) TCA cycle activity is low under the anaerobic treatment; and 3) microbial community composition differs between biomes and changes with oxygen availability.
Results/Conclusions
We found low PPP activity relative to glycolysis in the marsh sediment under aerobic and anaerobic conditions. High PPP activity was observed for the mineral soil, irrespective of oxygen availability. We observed conflicting results regarding TCA cycle activity in the sediment: higher 13CO2 production from 5-13C-glucose but not from 2-13C-glucose. Preliminary results from the 16S community composition analysis showed that the microbial community differed across biomes, but was not affected by oxygen availability. These results suggest that metabolic patterns can differ between ecosystems.