Dear colleagues,
Recently I anlayzed soil microbial C utilization pattern in two soils using BIOLOG Ecoplate. One soil is a climax forest soil in southern China with high substrate content (C, N, P etc) and soil microbial biomass and activity and a agricultural soil with relatively, and the other is a agricultural soil with relatively low substrate content and microbial biomass and activity. They were analyzed in the same procedure and the microplates have been incubated at 25 oC for 14 days. However, we found the results are very strange because AWCD of the foreset soil is very low (less than 0.3) while that of the agricultural soil is around 1.1. As I know, high AWCD indicates high microbial C utilization capacity but it seems wrong from our results. Is anybody familiar with the BIOLOG technique and could provide helps? Thank you very much.
Hui
@Farah Dear Farah, this data is BIOLOG AWCDs of the two soils during incubation period. The AWCD is much higher in the forest soil than in the agricultural soil than makes me confused. As I know, the forest soil has higher substrate content, microbial biomass and activity and dominated by bacteria. We estimated a opposite pattern between these two soils should occur. We cannot figure out why. Are you familiar with BIOLOG technique?
Dearest colleagues, I used BIOLOG several years ago, for tracking some specific rhizobial strain in the rhizosphere with relative success. I think that no technique alone is infallible itself. Perhaps in the forest soil you evaluated occurred sudden chemical processes that temporarily affected microbiota and thus seems lower microbial activity as compared with the agricultural soil. I recommend you to try with other parallel techniques before going into a desperation conclusion. By the way: are you sure that in the agricultural soil no biofertilizers were applied prior to the evaluation? Hope I could help you with my modest comments.
@Carlos Thank you Carlos for your kindly reply. We also used PLFAs to investigate the total microbial size and community structure but the results will be returned soon. I will at least check whether the total PLFAs amount (indicating microbial biomass) is in the pattern as expected.
I have noticed, that the results of Biolog EcoPlate approach is pH-dependent. I have examined different soil types and found that in the lower pH there is a much lower substrates utilization.
Have you made any other determination to know the amount of microorganisms? Some authors criticize BIOLOG because the dye itself can be harmful to microorganisms. Is the inoculum density the same between the two soils?
In recent studies I received similar results. In soil with high content of C, N, biomass and high activity of dehydrogenases I obtained a lower AWCD, compared to soil with lower values of the above parameters. However, my EcoPlate results correlate with NGS results. That is, in soil with a higher AWCD we identified more different microorganisms. I think that the type and diversity of soil microorganisms is more important for the utilization of substrates on EcoPlate than their abundance (biomass content).
I have been using Biolog Ecoplates for some time. The soils I use are very near to neutral, so I use water. I do however see on the Biolog website that they now suggest using a buffer. Maybe that could work if you are looking at soils with high or low pH. I regard Biologs as a very efficient tool, but I should think that one tool is not enough. And my understanding is that Biolog Ecoplates show diversity rather than abundance. Jay Garland is on RG as far as I know and he has done a lot of work on Biolog Ecoplates.
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