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Effect of redox conditions on bacterial and fungal biomass and carbon dioxide production in Louisiana coastal swamp forest sediment

Seo, Dong Cheol, DeLaune, Ronald D.
Science of the total environment 2010 v.408 no.17 pp. 3623-3631
bacteria, carbon dioxide, cycloheximide, forests, fungi, global warming, greenhouse effect, microbial biomass, redox potential, sea level, sediments, streptomycin, swamps, wastewater treatment, wetland soils, Louisiana
Fungal and bacterial carbon dioxide (CO₂) production/emission was determined under a range of redox conditions in sediment from a Louisiana swamp forest used for wastewater treatment. Sediment was incubated in microcosms at 6 Eh levels (-200, -100, 0, +100, +250 and +400mV) covering the anaerobic range found in wetland soil and sediment. Carbon dioxide production was determined by the substrate-induced respiration (SIR) inhibition method. Cycloheximide (C₁₅H₂₃NO₄) was used as the fungal inhibitor and streptomycin (C₂₁H₃₉N₇O₁₂) as the bacterial inhibitor. Under moderately reducing conditions (Eh>+250mV), fungi contributed more than bacteria to the CO₂ production. Under highly reducing conditions (Eh≤0mV), bacteria contributed more than fungi to the total CO₂ production. The fungi/bacteria (F/B) ratios varied between 0.71-1.16 for microbial biomass C, and 0.54-0.94 for microbial biomass N. Under moderately reducing conditions (Eh≥+100mV), the F/B ratios for microbial biomass C and N were higher than that for highly reducing conditions (Eh≤0mV). In moderately reducing conditions (Eh≥+100mV), the C/N microbial biomass ratio for fungi (C/N: 13.54-14.26) was slightly higher than for bacteria (C/N: 9.61-12.07). Under highly reducing redox conditions (Eh≤0mV), the C/N microbial biomass ratio for fungi (C/N: 10.79-12.41) was higher than for bacteria (C/N: 8.21-9.14). For bacteria and fungi, the C/N microbial biomass ratios under moderately reducing conditions were higher than that in highly reducing conditions. Fungal CO₂ production from swamp forest could be of greater ecological significance under moderately reducing sediment conditions contributing to the greenhouse effect (GHE) and the global warming potential (GWP). However, increases in coastal submergence associated with global sea level rise and resultant decrease in sediment redox potential from increased flooding would likely shift CO₂ production to bacteria rather than fungi.