I need to store fresh soil samples for several weeks and want to avoid lysing microbial cells (so I cannot sterilize the soil), but at the same time minimise microbial activity.
But when I freeze the soil and thaw it again, I will also break some microbial cells. At least that's what I thought so far
But maybe the microbes in a Siberian soil are more adapted to cold temperatures than e.g. microbes in tropical soils?!
We also froze tropical soil samples at -20°C for this purpose. Don't know if it's perfect, but what else can one do? Would be interested to hear if there are other options.
Dear Verena,
if you change the oxygen content you will probably favor anaerobic or microaerophilic microorganisms. And of course if MOs do not have fresh substrate they will die or change anyway. Maybe you can freeze-dry soils.
BTW: Nice to read that you ended up in North Wyke, where I was also long time ago.
Hi Verena,
I am curious to know what is the end use of these soil samples (what type of analysis are you planning?). We have kept fresh soil samples stored at < 4 C for about 2-3 weeks for subsequent ‘soil microbial biomass C and N’ determination and for extraction of soil NH4 and NO3. At these conditions microbial activity is supposed to be minimal. It is very difficult to stop microbial activity completely, unless we sterile the soil. We have noted microbial activity (albeit at a low rate, as noted by N2O dynamics within the top 0-10 cm soil layer) under freezing soil conditions in the field (in southern Ontario, Canada).
Meanwhile I also found this paper: Stenberg, B., et al. (1998). "Microbial biomass and activities in soil as affected by frozen and cold storage." Soil Biology & Biochemistry 30(3): 393-402.
Nobody seems to have tested the effect of vacuum on soil microbes, but I agree with what Bruno said. If I freeze-dry the soil and re-wet it again, how big would be the proportion of lysed cells?! I know that drying and re-wetting cycles can lead to a release of phosphorus in soils
@ Susantha Jayasundara: I'm interested in microbial and plant-available phosphorus and want to find the best way of storing my samples (or at least the best compromise). Would you except then also to have some microbial activity when storing soil at -20C?
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