Root and the Rhizosphere

Question 1

Where does 80% of the sugar consumed in Europe come from?

Answer 1

The sugar beet (which is a root)

Excess also used for biofuel

Question 2

What is a nutriceutical? Example

Answer 2

Foods that people believe are good for their health

Example: American Ginseng

Question 3

What fertiliser is running low in stock?

Answer 3

Phosphate

Easily lost to insoluble, inaccessible forms

Question 4

What are corn rootworms?

Answer 4

Western corn rootworm and Northern corn rootworm are leaf beetles that feed predominantly on corn. Rootworms overwinter as eggs that were deposited by adult females in the soil during the late summer months of the previous growing season. Larvae feed on corn root systems for 3-4 weeks during which time they pass through 3 growth stages commonly referred to as the first, second and third instars (third is 1/2 an inch in length)

Question 5

What are two disease that rot the roots of plants?

Answer 5

Phytophthora

Rhizoctonia

Question 6

What are buttress roots?

Answer 6

Common in rainforests where soil is shallow but trees are tall
Can supply up to 60% of the anchorage of the plant

Question 7

What are pneumatophores

Answer 7

Produced by trees in aquatic habitats such as mangroves to access oxygen from the air

Question 8

4 types of root that make up root systems

Answer 8

• Basal (hypocotyl-borne root)
• Shoot-borne root
• Tap (embryonic first root)
• Lateral (branch of another root)

Question 9

Examples of tap roots

Answer 9

Carrots
Parsnip
Sugar beet

Question 10

Examples of shoot-borne roots

Answer 10

Prop roots

Buttress roots

Question 11

Lateral root example

Answer 11

Madder roots

Question 12

What occurs in the underground root communities?

Answer 12

• Competition for nutrients and water
• Cooperation to release nutrients
• Warn each other about pests and pathogens

Question 13

What do aquaporins allow?

Answer 13

Water molecules to pass through biological membranes without interacting with the hydrophobic interior of the membrane

Question 14

What does mineral uptake require?

Answer 14

Transport proteins

Some enter by passive diffusion and others by active transport

Question 15

How does water move up the xylem?

Answer 15

Due to the combined effects of transpiration, cohesion and tension. Evaporation from the leaf produces tension in the mesophyll cells, which pulls up a column of water

Question 16

What are the problems of lakes experiencing anthropogenic eutrophication?

Answer 16

• Turbidity: less light reaches submerged plants
• Sediment: shortens lifespan of lake
• Primary productivity much higher: extensive algal/bacterial blooms
• Dissolved oxygen decreases: organisms decompose and oxygen used by decomposers
• Decreased biodiversity of primary producers: eventually blue-green bacteria and some bulrushes dominate
• Fish populations dominated by surface-dwelling coarse fish eg pike and perch due to lack of oxygen
• Zooplankton decrease: fewer water plants to hide in
• Drinking water quality declines
• Water causes human health problems due to microbe-secreted toxins

Question 17

What happens to roots in low phosphate environment?

Answer 17

-Primary root growth strongly inhibited
-Root hair production and length increase
-More lateral roots form
-Extension of lateral roots
Improves phosphate uptake by increasing root absorption surface and by favouring foraging of topsoil, which is where phosphate accumulates as plant material decays

Question 18

How is nitrate fertiliser made?

Answer 18

Made from anhydrous ammonia which is produced in the Claude-Haber process
Very expensive due to high temperatures and pressures needed, and high carbon cost

Question 19

Why is half the nitrate applied not taken up by plants?

Answer 19

Nitrate very soluble in water
Leaching: nitrates dissolve in rain/irrigation water and enter field drains or watercourses
Farming responsible for 50% of nitrogen pollution in Europe

Question 20

How do roots grow where nitrate levels are high?

Answer 20

-More lateral root initiation
-Longer lateral roots
These chances in root architecture improve nitrate uptake by increasing the root absorption surface

Question 21

When was the Ordovician period?

Answer 21

490-443 Mya

Algal biofilms dominated as plant root systems had not yet evolved and broken down rocks and produced soils

Question 22

Silurian period

Answer 22

444-416 Mya

By early Silurian there were small land plants with shallow rooting structures that could accumulate some organic matter

Question 23

Devonian period

Answer 23

420-360 Mya

Root systems gradually evolved that could accumulate and hold deeper soils

Question 24

Gilboa mid-Devonian forest

Answer 24

“First forest”
Contained three types of tree-sized plant:
1. Very large, non-woody Eospeatopteris (hollow, reed-like, leafless)
2. Large, woody, scrambling aneurophytaleans (leafless)
3. Giant club moss (Lycopsida)

Question 25

How did root evolution benefit river banks?

Answer 25

In the late Silurian and Devonian, more complex and deep root systems formed. These stabilised river banks and allowed development of deep channels, meandering rivers and muddy floodplains

Question 26

Carboniferous period

Answer 26

359-299 Mya
Deep soils fully established
Soil provides opportunities for microorganisms
Rich habitat, copious food and moisture
The period that produced coal

Question 27

How long does it take to form 1cm of topsoil?

Answer 27

1000 years

Question 28

What is the largest terrestrial pool of carbon?

Answer 28

Soil

Question 29

How much animal life can live in one hectare of soil?

Answer 29

5 tonnes

Question 30

How much land on Earth has undergone soil erosion?

Answer 30

1/4 of vegetated land

Question 31

How much fertile land lost to erosion annually?

Answer 31

12 million hectares

Montgomery, 2007

Question 32

Mycorrhizas

Answer 32

Beneficial interactions between soil microorganisms (arbuscular mycorrhiza and ectomycorrhiza) and land plants

Question 33

Example of ectomycorrhizae

Answer 33

Paxillus involutus

Poisonous mushroom which forms ectomycorrhizae with pines and other tree species

Question 34

What eats white rot fungus (and what is latin name)

Answer 34

Phanerochaete velutina eaten by Collembola (springtails)

Question 35

What are endomycorrhizae also known as? + features

Answer 35

Vesicular-arbuscular mycorrhizae (VAM)
These fungi do not form a sheath around the root, but instead penetrate the cell walls and make a close association inside the plant cells
70% of plants have then, including all grasses (except sedges), most herbaceous plants and some trees
Structures inside cells are called arbuscules and are surrounded by a specially made plant membrane

Question 36

What is the effect of fertiliser addition on ectomycorrhizae?

Answer 36

Adding nitrogen fertilisers to soils containing mycorrhizae ruins the relationship between the fungus and plant
Recovery if ectomycorrhizae can happen 6-15 years after stopping the addition of nitrogen fertilisers

Question 37

How do nitrogen-fixing bacteria provide plants with nitrogen?

Answer 37

Nitrogenase inactivated by oxygen
Oxygen is a byproduct of photosynthesis so plant cannot fix nitrogen
Some bacteria fix nitrogen whilst living in soil and plants take up fixed nitrogen
Others live symbiotically inside root nodules which exclude oxygen (legumes produce CWDEs to let bacteria into its cells)