biol 346 lab 1

Worksheet for Lab 1: Soil properties and microbial cell counts /24 1. Report the average pH and standard deviation for the four pH treatments. (2 marks) Sample Calculation: Field soil pH in dH20 Average= 6.39+6.68+6.86/3 = 6.643 Standard Deviation= square root of sum of (6.39-6.64333)^2+(6.68-6.64333)^2+(6.86- 6.64333)^2/ n-1 =square root of (-6.38999667)^2+(0.036667)^2+(0.21667)^2 / 3-1 = square root of (40.83205744)+ (0.001344469)+ (0.046945889)/ 2 =square root of (20.39188354) = 0.237 Field Soil pH in CaCl2 Average= 5.613 Standard Deviation= 0.250 Forest Soil pH in dH20 Average= 5.347 Standard Deviation= 0.075 Forest Soil pH in CaCl2 Average=4.277 Standard Deviation=0.047 2. What are the advantages/disadvantages of the two techniques used (H2O and CaCl2)? Did the choice of technique influence your result, or are pH trends robust between both types of measures? (Note: See the Ohio State University lab manual excerpt posted on LEARN for clarification on this point) (3 marks) One of the disadvantages of using the technique of finding the active acidity in soil using CaCl2 is that if there is an overwhelming amount of cations there will be a decrease in buffering capacity therefore the amount of CaCl2 that can be used is limited unlike H2O. An advantage of using CaCl2 is that it can act as a sink or source for soil acidity. When active acidity is increased, acid cations have a sink from the exchange complex. And conversely, when active acidity is decreased the exchange complex becomes a source. Choice of technique does not influence my results as much since the exchange complex can absorb H+ allowing for very little effect on the active acidity, as well as being buffered against change. 3. Report the average wet weight, dry weight, water weight, and % moisture, along with the standard deviation for % moisture for the field and forest soils (2 marks)

Field Soil (subtracting tray weight from each) Average wet weight= 10.1117g Average Dry weight= 8.3522g Average water weight= 1.7595g Average % moisture= 17.4% Standard Deviation= 0.2309% Forest Soil Average wet weight= 10.1418g Average Dry weight= 8.0530g Average water weight= 2.0888g Average % moisture= 20.6% Standard Deviation= 0.0238% 4. Provide a table of your plate count results, similar to the one in the lab manual but with all media and both soils included. State which dilution you selected for your calculations for each soil and medium combination. (4 marks) Forest Soil Field Soil A B C A B C AA 10^-2 TNTC TNTC TNTC TNTC TNTC TNTC AA 10^-3 65 74 78 TNTC TNTC TNTC AA 10^-4 6 10 12 40 55 60 AA 10^-5 NA NA NA 13 9 8 NA 10^-2 TNTC TNTC TNTC TNTC TNTC TNTC NA 10^-3 TNTC TNTC TNTC TNTC TNTC TNTC NA 10^-4 TNTC TNTC TNTC TNTC TNTC TNTC NA 10^-5 21 13 21 61 79 53 NA 10^-6 4 5 5 9 8 7 SEA 10^-2 TNTC TNTC TNTC NA NA NA SEA 10^-3 174 162 120 TNTC TNTC TNTC SEA 10^-4 42 49 34 183 176 179 SEA 10^-5 12 16 6 65 57 55

number of colonies unable to be counted in even the higher diluted samples. AA was the agar in which the fewest of morphology colonies were formed. When comparing NA and SEA media it can be seen that both of these agar allowed a numerous amount of colonies to form however the NA agar still showed to have more variable colonies and a higher number. It is evident that these media select for different microorganisms. The nutrient agar is an all around agar that allows for favorable conditions for a lot of microbes to form colonies that is why it is expected to have a high plate count. However, Soil Extract Agar selects specifically for microbes within soil particularly to be favorable to this agar. Therefore, it can be distinguished that microbes normally forming within soil were selected for by the SE Agar. 7. Describe the key limitations of the methods used, as well as (briefly) sources of error. (2 marks) Some key sources of error that could be made using the methods used is that inaccurate transferring will lead to less accurate dispensing and could ultimately lead to different results. As well, when doing variable counts, the higher the dilution is, the more likely an error can be made in counting. 8. How might pH, soil moisture, or land use type affect the microbial communities at the two sites? Could these changes be measurable by a plate count? If not, what other methods might be needed? (4 marks) pH, soil moisture and land use type can certainly affect the microbial communities at the two sites. Having a higher pH in soil can affect the types of microbial communities present in the soil. High pH can be an unfavorable condition for certain microbes and therefore if a soil has higher pH fewer microbial communities may be present or specific pH resistant microbes will be present instead. Soil moisture also has the same effect where higher moisture would be more favourable for certain microbial communities while dryer soil may be unfavorable. These changes can be measurable by plate count due to seeing how many colonies are able to form in soils of different environments. For instance, a soil with more neutral pH and abundance of moisture may have a lot higher plate count and more colonies will form compared to a soil sample of high pH. Some other methods that could be used or might be needed is a method to identify and characterize the microbial colonies present in the samples. If one were able to identify the microbes, it can be possible to see that the soil with the more favorable conditions may have a larger variety of different microbes present as well as an abundance of them. While soil with unfavorable microbial conditions may only show and allow identification of certain microbes that are resistant to the unfavorable conditions.