I did a 7-day incubation for several different soils (16 to 44 g/kg C, 0.3 to 3.5 g/kg N, and 11 to 76 CN ratio), keeping a 60% field capacity during this period without adding any other substates. Interestingly, the MBC, MBN, and their ratio all decreased after 7 days(180 to 100 ug/g MBC, 19 to 13 ug/g MBN, 10 to 9 for MBC/MBN ratio). Can anyone tell what mechanisms are controlling such process? Or osmotic shock? I thought the MBC should be higher after incubation as they will be more active when have optimum soil moisture (60% FC).
Another possible consideration is whether you seived your soil just prior to the experiment, and what type of soils you were working with (fungal to bacteria ratios). Seiving will break a lot of fungal hyphae. That might stimulate bacteria which have a lower C:N ratio than fungi.
Are yours closed systems? Did you dry and/or sieve your soils before incubation? If so, you may have depletion of oxygen and increase in CO2 inside your microcosms, because of the stimulation of the microbiota caused by aeration. Besides, an enhanced activity may also deplete your substrate of carbon and other nutrients. Also, if microbial activity was stimulated by previous soil handling, you started with a stimulated microbiota that will eventually stabilise back to its original, lower, levels (or close) if stimulation is not continued.
Yes, I used closed jars (470 ml) with 40 g soil inside, and without adding any substrate. Oxygen may be one of the factors. Thank you.
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