I want to study cover crop biomass application to the methanogenesis in rice paddy soil
Proportion study? Do you mean proportion of hydrogenotrophic methanogenesis to acetoclastic methonogenesis in rice field?
Yes may be but we have previously we have studied the effect of different application rate of cover crop biomass on methane and carbon dioxide emission in rice paddies, and we found that at 12 Mg/ha there was was a dramatic increase in methane emission as compared to Co2 emission. so i want to study what was the reason for such huge difference?
The figure attached may be helpful about what i want to ask about?
You can do some hydrogenotrophic ativity tests.. (see attached file) or do a detailed molecular characterization of the sample by high-throughput sequencing
I suspect that at increasing loading rates the amount of crop biomass degraded under anaerobic conditions increases relative to the amount that is degraded under aerobic conditions. The former process produces both CH4 and CO2, the later only CO2. Thus with increasing loading the ratio of CH4 over CO2 increases. In other words/my hypothesis: what you observe is not so much CO2 removal by hydrogenotrophic methanogens, but rather a shift in electron acceptor.
The problem is because of complex microbial community, there might also be acetogen, which can convert co2 to acetate and this acetate might be used to produce methane by acetoclastic methanogens. So difficult to determine increase methane and decrease co2 is dute to hydrogenotrophic methanogen or combine effects of acetogens and acetoclastic methanogens. The delta signature of methane gas produce by different type of methanogen is also same (as per my knowledge). Analysis of microbial community/ type of methanogens may help.
Actually, the ultimate ratio of CH4 to CO2 produced from the degradation of organic material is independent of the pathway taken. If for example hydrogen is produced from the degradation of glucose, it does not matter whether this hydrogen is subsequently directly converted into methane, or first converted into acetate with the acetate subsequently converted into methane. In either case the mineralization of one mole of glucose yields 3 moles of CH4 and 3 moles of CO2 (see below).
Classical pathway:
C6H12O6 + 2H2O --> 2CH3COOH + 2CO2 + 4H2
CO2 + 4H2 --> CH4 + 2H2O
2CH3COOH --> 2CH4 + 2CO2
SUM: C6H12O6 --> 3CH4 + 3CO2
Pathway where hydrogen is removed by acetogens:
C6H12O6 + 2H2O --> 2CH3COOH + 2CO2 + 4H2
2CO2 + 4H2 --> CH3COOH + 2H2O
3CH3COOH --> 3CH4 + 3CO2
SUM: C6H12O6 --> 3CH4 + 3CO2
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