Soil Food Web 1
What is the rhizosphere?
The soil surrounding a root and influenced by root exudates.
Why are there higher numbers of microbes in the rhizosphere than in the rest of the soil?
The plant feeds the microbes with its exudates.
Why is bulk density important?
It indicates how much pore space is in a soil. It indicates how compacted a soil is.
How do bacteria contribute to soil aggregation?
They excrete sticky substances that glue soil particles together.
When using a microscope, which objective lens do you start with?
4X, the lowest power, the shortest one
Some fungi catch and eat nematodes. How do they do it?
They form loops of hyphae and when a nematode puts its head through a loop, it contracts and catches the nematode.
What are the 3 classes of protozoa?
Amoeba, flagelate, cilliate
What is the relationship between bulk density and porosity?
Lower bulk density means higher porosity
How do fungi cintribute to soil aggregation?
They excrete substances that soil stick particles together (for example Glomalin) and their hyphae wrap around soil particles, holding them together.
When do you use the coarse focus on a microscope and when do you not use it.
Use the coarse focus to obtain the initial focus with the lowest power objective lens. Do not use it with higher power objective lenses.
How do both the plant and the fungus benefit from a mycorrhizal relationship?
The fungus gains food from the plant in the form of sugars and other organic compounds. The plant gains water and mineral nutrients that the fungus extracts from the soil.
What are the 2 most common types of mycorrhizal fungi and what is the main difference in how they interact with the plant root?
Endomycorrhizal fungi extend into the cells of plant roots. Ectomycorrhizal fungi surround the root and grow into the plant root but remain between the cells, not inside of the cells.
What is bulk density and how is it measured?
It is the weight per volume of soil as it is on site. It is measured by collecting a known volume of soil without compacting it or disturbing it's structure and finding the dry weight of the soil.
What are 2 ways that plant roots contribute to soil aggregation?
They excrete polysaccharides that stick soil particles together and their roots wrap around soil particles, holding them together, and they feed bacteria and fungi that also contribute to soil aggregation.
Describe how to make a 1:10 dilution of a soil sample for microscope viewing.
Start with 1 ml of soil and add water until the total is 10 ml.
What are 3 benefits of mycorrhizal fungi?
They provide mineral nutrients to the plant, protect the plant from pathogens, improve soil aggregation, increase accumulation of organic matter in the soil, decompose organic matter, and are food for some other organisms in the soil food web.
Different types of nematodes eat different things. What are 3 things a nematode might eat?
Bacteria, fungi, other nematodes, plants.
Why is aggregate stability important?
Stable aggregates will maintain soil structure even with disturbance, such as tillage, moving water, or the impact of rain drops.
In what way do bacteria and fungi each influence soil pH?
Bacteria increase pH, fungi decrease pH.
How do the populations of bacteria and fungi change as a plot of land goes from disturbed soil and weeds to grasses to perennials to shrubs to forest?
The amount of bacteria stays about the same but at each step there is more fungi, resulting in a higher fungal to bacteria ratio.
Describe the steps and the types of organisms involved starting with plant roots exuding sugars and ending with the plant roots absorbing needed minerals.
Bacteria and fungi eat the sugars and other plant exudates. The bacteria and fungi digest organic matter and use their enzymes and organic acids to extract minerals from soil particles. Protozoans, microarthropods and nematodes eat the bacteria and fungi and excrete some of minerals that the bacteria & fungi got from the organic matter and soil particles. These minerals are excreted in forms that the plant can easily take up and use.
Relate the Science of Consciousness principle that the whole is more than the sum of the parts to the soil food web.
Each member of the soil food web is just doing what it needs to do to gain nourishment and survive, but the soil food web, as a whole, creates healthy soil, healthy plants, healthy people and other animals that eat the plants, prevents erosion, sequesters carbon, etc.
When we measure soil respiration, what are we measuring and what does it mean?
We are measuring the CO2 given off by the respiration of soil organisms and it gives an indication of how many and how active the organisms are. More CO2 means more activity of soil organisms.
What are mineralization and immobilization?
Mineralization is making plant nutrients into soluble mineral forms, such as nitrate and ammonium. This happens when a predator eats an organism and it's waste contains the unneeded nutrients. Immobilization is when an organism consumes a soluble nutrient and incorporates it into its body.
What types of plants do ectomycorrhizal fungi associate with?
Conifers and some hardwood trees