Welcome to BIO121/ESS120: Introduction to Environmental and Ecological Microbiology at UC Merced! This page provides additional online content associated with the course, including short video lectures by Professor Beman, additional videos and interactives, and additional reading materials.
Terrestrial Microbiology – Part 2
We previously learned about microbial life in soil and how water affects soil microbes. We saw that water supplied via precipitation or irrigation can eventually lead to methanogenesis in soils due to changes in redox conditions. We also read an intro to Earth’s climate system, which sets up this second session on terrestrial microbiology.
This week we will examine the variations in soil microbiology that occur across Earth’s land surface. We will see how these variations relate to the dominant plant types found in different ecosystems, as well as to different soils found in different locations. And, as we will see, all of these are connected to climate.
A key point is that soil microbes are constantly interacting with land plants, leading to some interesting patterns across soils. We will then see some implications of this, including the question you have all been asking, ‘why is ground brown?’ You’ll see that this isn’t as stupid as it sounds!
5.1 Climate and Biomes. One of the most striking patterns that we see across Earth’s surface is the variation in plants. Even from satellite images or photos from the moon, you can see dark green forests in some areas, and tan deserts in other areas. Last week you read an intro to the climate patterns that we see across Earth’s surface. Precipitation and temperature, in turn, dictate which ‘biomes’ are found in different locations. (You may have learned this concept before.)
Please read this article that covers Earth’s terrestrial biomes, paying particular attention to Figures 1 and 4. I also think it is really interesting to see the variations in different locations across the Earth, see photos of this, and think about where I’d love to travel in the future.
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5.2 Soil Formation. You just read about how climate affects the distribution of biomes. Climate is also one important influence on the formation of soils. Please read this page from the Soil Science Society of America, which briefly discusses soils and how they form, including the strange but useful acronym ‘CLORPT:’
https://www.soils.org/about-soils/basicsLinks to an external site.
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5.3 Soil Orders. The differences in soils that you just read about lead to the concept of organizing soils into different ‘soil orders.’ The US Department of Agriculture recognizes 12 soil orders (which you may have seen pictures of). This page from the University of Idaho provides a good introduction to the 12 soil orders. Please first read the general overview, then click through each of the soil orders to learn about them. Be sure to view the images/diagrams below the text, as these are most interesting:
https://www.uidaho.edu/cals/soil-ordersLinks to an external site.
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5.4 Global Soil Microbiology. You just learned about how climate patterns affect which biomes are found where, and especially that forests are found where precipitation is high enough to allow large trees to grow (in the tropics and near 60 degrees north and south latitude). You also read about how climate patterns affect soil formation and orders. In this video lecture, we will see how this results in one major pattern in soil microbes. (Note that there are several ways to pronounce ‘fungi’ that vary from place to place. I use several of them here. Fun-guy, fun-gee, and fun-jai are all ok by me!)
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5.5 Soil Microbial Ecology. In this video lecture, we will take a more detailed look at some of the ecological patterns displayed by soil microbes. Much of this is very new information due to the development of new DNA/RNA sequencing technologies, as well as coordinated sampling around the world. (We will get into some of the technical details later on.) We will cover scientific papers directly from the literature. Pause, rewind, and take notes, as there is significant scientific detail here!
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5.6 Brown Ground. This video lecture covers the paradox of the ‘brown ground.’ We spent a week learning that oxygen is a great oxidant and organic matter is a great reductant, falling towards the top and bottom of the redox ladder. Many living things make use of this to generate energy, and so we are dependent on oxygenic photosynthesis to produce oxygen and organic matter.
But not all organic matter that is produced is consumed! The organic matter in soils comes from plants and gives soils their darker colors—i.e., the ground is usually brown. This sounds stupid, but when you think about it from a redox standpoint, why is there any organic matter present in soils? Organic matter is present, but so is oxygen (except when soils are flooded with water)—so why isn’t all the organic matter consumed by soil microbes that oxidize organic matter using oxygen? Why is the ground still brown? That brown color—organic matter—represents a source of energy! This is the paradox, and we discuss some of the reasons for this in this video lecture.
Pause, rewind, and take notes, as this covers a lot of scientific ground…
Beman Lab, University of California, Merced 