I am running the classical substrate induced soil respiration experiment. There are four treatments: control without any inhibitors, with cycloheximide (fungicide), with streptomycin (bactericide), and with both inhibitors. I ran the CO2 with time, but found the addition of cycloheximide increased the respiration instead of decreasing. I redid the experiment twice but same results. Do you know why this happened ? It was said that cycloheximide could decompose under alkaline condition. Our soils are ph 8. Could that be the reason? What other fungicide I can use? Also considering the price. Thank you!
cycloheximide is generally used only in in vitro research applications, and is not suitable for human use as a therapeutic compound. Although it has been used as a fungicide in agricultural applications, this application is now decreasing as the health risks have become better understood.
If you measure substrate induced respiration of cycloheximide treated soil the respiration curve will show an other shape: The maximum of the growth peak will delay, normally you can see double peaks, and the cumulative respiration will become higher. Reasons: Cycloheximide inhibits fungi growth. This results in the peak delay. But unused substrate will consumed. Bacteria (and some fungi that are not completely inhibited by cycloheximide) will grow an consume the substrate. This result in the second later peak. And due to the period after substrate addition you will include respiration of dead fungi and cycloheximide itself - remember any organic compound will be respirated - earlier or later...
[In Bartling et al. 2009 (DOI: 10.1016/j.chemosphere.2009.10.024) you can see in figure 2 an example of such a respiration curve.]
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