Biosphere III

Question 1

How does shoot biomass vary between communities with only plants, plant and bacteria, and plants, bacteria, and protozoa? Explain why.

Answer 1

From lowest to highest: plants, only, plants and bacteria, protozoa. This is because plants grow best with a complete community, and the additional microfauna help with nutrient cycling and the retention of nutrients in biomass, including nitrogen.

Question 2

What is the role of nematoda in soil?

Answer 2

They occupy multiple trophic levels and can prey on plant roots, bacteria, and fungi. They can be free living or parasitic.

Question 3

How can different types of nematodes be distinguished from one another?

Answer 3

They can be distinguished by their mouthparts.

Question 4

Describe the impact of parasitic nematodes on ecosystems.

Answer 4

They can infect plant roots, forming root lesions and draining the plant’s photosynthate and nutrients. It is the cause of 5% of global crop loss.

Question 5

What preys on parasitic nematodes?

Answer 5

Over 200 species of predatory fungi.

Question 6

Name 2 ways to reduce parasitic nematode populations.

Answer 6

1. Crop rotation, which can interrupt their lifecycle.
2. Increase OM to increase fungal abundance, which will reduce their populations.

Question 7

How big are soil mesofauna?

Answer 7

100 micrometers to 2 mm.

Question 8

What are the main roles of soil mesofauna?

Answer 8

They are key for litter fragmentation. They are decomposers, predators, and herbivores.

Question 9

What are the two major types of soil mesofauna? Which is more common?

Answer 9

Collembola (springtails) and soil mites (acari). Mites are more common.

Question 10

Where are collembola and mites located in the soil?

Answer 10

Collembola are located near the surface and soil mites are located throughout the soil profile.

Question 11

Compare the diets of collembola and mites.

Answer 11

Collembola: mostly eat plant litter and fungal hyphae
Mites: mostly eat plant detritus, sometimes microbial predators

Question 12

what is the major significance of collembola in the soil ecosystem?

Answer 12

They are responsible for 30% of respiration of all soil invertebrates

Question 13

What is the major significance of soil mites in the soil ecosystem?

Answer 13

They are early colonizers of organic matter in the early stages of decomposition.

Question 14

How can decomposition be measured in the field?

Answer 14

Put litter in a bag and weight it. Then weight it after some time has passed. The difference corresponds to how much has been lost to decomposition. The size of the holes in the bag dictates what soil organisms can access it and contribute to decomposition.

Question 15

Describe how decomposition rates changes between litter bag mesh sizes of 0.01 mm, 0.1 mm, 1 mm, and 7 mm.

Answer 15

0.01 mm: all fauna excluded, no decomposition.
0.10 mm: microfauna only, some decomposition
1 mm: microfauna and some mesofauna, more decomposition
7 mm: microfauna and mesofauna but no macrofauna, even more decomposition

Question 16

How big are soil mesofauna?

Answer 16

100 micrometers to 2 mm.

Question 17

How big are macrofauna?

Answer 17

> 2 mm

Question 18

What is the major role of macrofauna? Explain what this means.

Answer 18

They are ecosystem engineers. This means that they make major alterations to their physical environment that influence the habitats of many other organisms.

Question 19

Give 4 examples of soil macrofauna.

Answer 19

Earthworms, gophers and other rodents, termites, ants

Question 20

Name 2 ways in which earthworms influence soil fertility.

Answer 20

They burrow, which provides important pathways by which roots can penetrate dense soil layers and increase water infiltration.

They ingest soil and expel it and casts of OM mixed with mineral soil. This enhances the aggregate stability of the soil.

Question 21

How do earthworm casts compare to soil in terms of:
a) Bulk density
b) Structural stability
c) CEC
d) Soluble P

Answer 21

a) Lower in cast than soil
b) Higher in cast than soil
c) Higher in cast than soil
d) higher in cast than soil (very nutrient rich)

Question 22

What is the northern earthworm dilemma?

Answer 22

Earthworms have been spreading into boreal forests with climate change. This increases decomposition rates in these ecosystems and increases nitrogen availability to plants. These nutrients allow nonnative plants to thrive, which can push out endemic plants and change the composition of Boreal forests.

Question 23

What role can termites play in ecosystems?

Answer 23

They can hold back desertification in dryland ecosystems by changing the moisture and chemistry in the soil around their mounds, as they hold water and nutrients well.

Question 24

Describe how termites interact with other organisms in the soil.

Answer 24

Termites will forage and consume woody materal, which they will excrete. Fungi will then break it down and release nutrients. These nutrients can then be taken up by the terminates again (not sure)

Question 25

Do ecosystem engineer alter the physical or chemical environment in soil?

Answer 25

Both. In altering the physical environment, they alter the chemical environment as well.

Question 26

What is the rhizosphere?

Answer 26

It is the zone of the root’s influence on the soil.

Question 27

What are the major characteristics of the rhizosphere?

Answer 27

It is nutrient and energy rich.

Question 28

How does the quantity and diversity of microoganisms in the rhizosphere compare to the rest of the soil?

Answer 28

Because the root can create a unique environment, it selects for specific species from the general pool in the soil. There is typically less diversity right around the root, but the species there usually have unique capacities to boost plant growth. In terms of quantity, microbes are 10X to 100X more numerous in the rhizosphere than in the bulk soil.

Question 29

What are mycorrhizae?

Answer 29

Mycorrhizae is the symbiotic relationship between fungi and roots.

Question 30

How many plants make myccorhizal associations?

Answer 30

70-80%.

Question 31

What are the two major types of mycorrhizae?

Answer 31

Ecto-mycorrhizae and arbuscular mycorrhizae.

Question 32

What do plants and fungi provide one another with in mycorrhizal trade?

Answer 32

From the fungus: nutrients (N, P) and water
From the plant: sugars from the carbon they fix

Question 33

Name 3 benefits of mycorrhizae.

Answer 33

1. Increases soil volume that can be accessed by the plant, thus more nutrient and water uptake
2. Organic matter breakdown
3. Provide resources for saprotrophs