Root and the Rhizosphere Flashcards
Where does 80% of the sugar consumed in Europe come from?
The sugar beet (which is a root)
Excess also used for biofuel
What is a nutriceutical? Example
Foods that people believe are good for their health
Example: American Ginseng
What fertiliser is running low in stock?
Phosphate
Easily lost to insoluble, inaccessible forms
What are corn rootworms?
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)
What are two disease that rot the roots of plants?
Phytophthora
Rhizoctonia
What are buttress roots?
Common in rainforests where soil is shallow but trees are tall
Can supply up to 60% of the anchorage of the plant
What are pneumatophores
Produced by trees in aquatic habitats such as mangroves to access oxygen from the air
4 types of root that make up root systems
- Basal (hypocotyl-borne root)
- Shoot-borne root
- Tap (embryonic first root)
- Lateral (branch of another root)
Examples of tap roots
Carrots
Parsnip
Sugar beet
Examples of shoot-borne roots
Prop roots
Buttress roots
Lateral root example
Madder roots
What occurs in the underground root communities?
- Competition for nutrients and water
- Cooperation to release nutrients
- Warn each other about pests and pathogens
What do aquaporins allow?
Water molecules to pass through biological membranes without interacting with the hydrophobic interior of the membrane
What does mineral uptake require?
Transport proteins
Some enter by passive diffusion and others by active transport
How does water move up the xylem?
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
What are the problems of lakes experiencing anthropogenic eutrophication?
- 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
What happens to roots in low phosphate environment?
-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
How is nitrate fertiliser made?
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
Why is half the nitrate applied not taken up by plants?
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
How do roots grow where nitrate levels are high?
-More lateral root initiation
-Longer lateral roots
These chances in root architecture improve nitrate uptake by increasing the root absorption surface
When was the Ordovician period?
490-443 Mya
Algal biofilms dominated as plant root systems had not yet evolved and broken down rocks and produced soils
Silurian period
444-416 Mya
By early Silurian there were small land plants with shallow rooting structures that could accumulate some organic matter
Devonian period
420-360 Mya
Root systems gradually evolved that could accumulate and hold deeper soils
Gilboa mid-Devonian forest
“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)
How did root evolution benefit river banks?
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
Carboniferous period
359-299 Mya Deep soils fully established Soil provides opportunities for microorganisms Rich habitat, copious food and moisture The period that produced coal
How long does it take to form 1cm of topsoil?
1000 years
What is the largest terrestrial pool of carbon?
Soil
How much animal life can live in one hectare of soil?
5 tonnes
How much land on Earth has undergone soil erosion?
1/4 of vegetated land
How much fertile land lost to erosion annually?
12 million hectares
Montgomery, 2007
Mycorrhizas
Beneficial interactions between soil microorganisms (arbuscular mycorrhiza and ectomycorrhiza) and land plants
Example of ectomycorrhizae
Paxillus involutus
Poisonous mushroom which forms ectomycorrhizae with pines and other tree species
What eats white rot fungus (and what is latin name)
Phanerochaete velutina eaten by Collembola (springtails)
What are endomycorrhizae also known as? + features
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
What is the effect of fertiliser addition on ectomycorrhizae?
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
How do nitrogen-fixing bacteria provide plants with nitrogen?
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)
