Module 4: Loss of Soil Biodiversity

Question 1

What are the main groups of soil organisms? And how do they interact?

Answer 1

MACRO-ORGANISMS:
1. Plants
2. Soil fauna:
a. without legs (e.g. worms, pot worms)
b. with legs (e.g. springtails, mites, isopods)

MICRO-ORGANISMS:
3. Soil microbes:
a. Fungi
b. Bacteria
4. Soil micro-fauna (e.g. nemathodes)

Question 2

What is the relationship between soil biodiversity and soil functions?

Answer 2

In the soil food web, nutrients are in excess and thus made available for the plants. In the mineral cycle soil biodiversity plays an important role.

Question 3

What are the processes that cause a loss of soil biodiversity and what are their effects?

Answer 3

Threats to the things they need to survive: water, air, or food.
1. Water: too much, too little, low quality (e.g. salinity, pollution)
2. Air: too little air through soil sealing, soil compaction
3. Food: no plants due to deforestation, overgrazing, …

Question 4

What are measures and strategies to prevent loss of soil biodiversity?

Answer 4

Avoid pollution, maintain nutrient balance, feed soil biota with SOM, maintain vegetation, prevent erosion through terracing and contour working,

Question 5

What are nematodes?

Answer 5

Very small worms only visible with a microscope.

Question 6

How are soil organisms classified?

Answer 6

By their waist circumference.

Question 7

What are hypha? What are they collectively called?

Answer 7

The long, branching, filamentous structures of fungi. This is their main mode of vegetative growth and collectively called mycelium.

Question 8

What are protozoa? How are they different from bacteria?

Answer 8

Protozoa are one-celled organisms, like bacteria. But they are bigger than bacteria and contain a nucleus and other cell structures, making them more like plant and animal cells.

Question 9

What is this organism?

Answer 9

Springtail

Question 10

What is this soil organism?

Answer 10

Isopods

Question 11

What is this soil organism?

Answer 11

Protozoa

Question 12

What are the trophic levels in the soil food web?

Answer 12

1. Autotrophs: the plants that make energy from carbon dioxide, sunlight, water and nutrients.
2. Lowest trophic level: primary consumers. Fungi, bacteria, plant-eating nematodes.
3. Secondary consumers: fungivores and bacterivores. Protozoa, bacterial & fungal feeding nematodes, fungal feeding mites, fungal feeding springtails.
4. Tertiary consumers: carnivores. carnivorous nematodes, -springtails, -mites. Centipedes!!

Question 13

What is detritus? What are the organisms that feed on it? Provide examples.

Answer 13

Detritus = plant residue/litter. The organisms that feed on it are called detrivores. For example: bacteria, earth worms, pod worms, isopods.

Question 14

What functions do soil organisms have in general?

Answer 14

1. Help produce soil organic carbon and cycle nutrients.
2. Provide nutrients for plants.
3. Medical purposes, e.g. discover new forms of antibiotics
4. Soil structure formation
5. Decompose pollutants.
6. Disease & pest regulation
7. A quarter of world’s biodiversity is harboured.

Question 15

How are soil organisms categorised?

Answer 15

By their width and length: micro-organisms, mesh-organisms, and macro-organisms.

Question 16

What is the biomass associated with each of the categories of soil organisms and what are their roles?

Answer 16

Meso-organisms: they feed on microbes and other soil organisms. Therefore they decompose litter, mineralise nutrients, and control pests and disease. Rewatch video 4.3.1 from 5.00 a few minutes.

Question 17

What is bioturbation and how does it link to the “ecosystem engineers”?

Answer 17

Bioturbation is the alteration of soil structure and sediments. Ecosystem engineers make biotic and abiotic changes to the soil.
- Their burrows improve soil airation and infiltration.
- They create new habitats for other soil organisms.
- Their casts are decomposed organic and nutrients aggregated.

Question 18

What kinds of roots do plants have?

Answer 18

Primary, secondary, and root hair roots. The root hairs are mainly responsible for nutrient and water uptake as they can branch out into the soil.

Question 19

What mutually beneficial symbiosis do legume roots and soil organisms have?

Answer 19

Legumes for symbiosis with fungi and bacteria.
1. FUNGI: specifically mycorrhizal fungi. C: plant –> fungus. P: fungus –> plant. They have arbuscular mycorrhizal fungi AMF.
2. BACTERIA: rhizobia.
C: plant –> rhizobia. N: rhizobia –> plant.
Legumes specifically grow nodules in their roots which house the rhizobia that fixate N from the air for the plant.

Question 20

Which two types of mycorrhizal fungi are there?

Answer 20

1. Arbuscular mycorrhizal fungi that live inside the root and in the soil.
2. Ectomycorrhizal fungi. These live outside of the root. Trees often have these.

Question 21

What does soil life need in order to perform its functions?

Answer 21

1. Water –> 25%
2. Air –> 25%
3. Food: soil organic matter –> 5%
   (4. the rest of the soil is mineral particles and covers the remaining 45%)

Question 22

What are measures and strategies to resolve loss of soil biodiversity?

Answer 22

Remediate polluted soils through phytoremediation, revegetation against erosion, revegetation of desired plants to re-establish nutrient balances. Diminish soil sealing by creating small green patches.

Question 23

What are the different forms of phytoremediation?

Answer 23

1. Phyto-extraction: the plant takes up the pollutant which is then removed with the plant.
2. Phytostabilisation: pollutants are made less mobile through root exudates.
3. Photo-stimulation: the plant stimulates the soil biota to degrade the contaminants.
4. Photo-degradation: certain plants produce enzymes that degrade pollutants in their roots.