WEEK 7 LECTURE- PLS-1-Root Systems and Soil Formation Overview

Interactions with symbionts

The relationship roots have with other organisms that can benefit the plant.

Dicots roots

typically have taproots.

Monocot roots

typically have fibrous roots.

Primary roots

Roots formed from the radicle in the seed that give rise to secondary roots.

Seed coat

The protective outer layer surrounding the seed.

Cotyledon

The seed leaf within the seed.

Plumule

The beginning state of the shoot or stem.

Epicotyl

Part of the early stem within the seed.

Hypocotyl

The early part of the stem within the seed.

Hilum

The part that attaches the early seedling to the inside of the seed.

Micropyle

A small opening in the surface of the ovule.

Adventitious root

Roots that form from stems or leaves.

Adventitious prop root

A type of adventitious root that provides support.

Buttress Roots

Large above-ground roots that provide structural support.

Taproot

A single, thick primary root that grows downward, adapted for anchoring and storing nutrients.

Fibrous Root

Many small roots efficient for absorbing water and nutrients from soil.

Aerial Root

Roots that grow above ground or above water. This is a type of adventitious root, While they both grow from the stem, some adventitious roots may grow on the underground part of the stem, so this is a differentiating term between the two.

Storage Root

Roots modified to store nutrients and water. sweet potato and carrots are examples.

Haustorial Root

A parasitic root that burrows into a host plant to steal water and nutrients.

Root Hairs

Extensions of the epidermis of the root that absorb most of the water.

how to identify cross section of Dicot Root

Characterized by a star or x shape to the vascular bundle.

how to identify Monocot Root

Characterized by a ring shape of the vascular bundle.

Pericycle in roots location and function

Layer just inside the endodermis that controls secondary root growth in the root (controls secondary vascular growth in the stem)

Endodermis

The layer just outside the pericycle that regulates the flow of water and nutrients in and out of the vascular bundle.

Suberin

A substance that coats the endodermis and controls water and nutrient entry. Stops

Epidermis

The outer-most layer of cells that protects the root and aids in water absorption.

Exodermis

The secondary layer beneath the epidermis that reduces water loss.

Cortex

Layer of parenchyma cells for storage and transport of nutrients.

Vascular Cylinder

Located at the center of the root containing xylem and phloem tissues.

Xylem

Transports water and dissolved minerals from roots to the rest of the plant.

Phloem

Transports sugars and other metabolic products downward from leaves.

Monocot Roots how to visually identify

Phloem cells are interspersed in a circle pattern between the xylem cells.

Pith definition, makeup and function

In monocot roots not dicot roots, it is the central part of the vascular system, made up of parenchyma cells, involved in storage.

Secondary growth occurs in monocots or dicots roots?

Dicots undergo secondary growth while monocots do not.

Water Uptake in Roots occurs through what process- describe the process

Water enters the roots through osmosis, because the water concentration outside the root is greater than that of the water concentration inside the root.

Osmotic Pressure Control- define

Roots can intake solutes like phosphorus to lower the water concentration inside the root, making uptake easier with lower water availability outside the root.

Water Cycle in Plants

Water goes from the soil, into the root, up the plant, and out into the atmosphere in a constant cycle.

Simplastic Flow

Water moves through the cells via chloroplast. this process is more selective, and slower.

Cortex Tissue

Water moves through cortex tissue, which are underground parenchyma cells, for short-distance transport and storage.

Casparian Strip

The Casparian Strip is located on the outside of the endoderm and stops symplastic movement of water into the vascular bundle.

Apoplast Pathway

Movement of water and solutes around the cells, via the extracellular spaces

Pros of Apoplast Pathway

Fast transport, bypasses membrane and transport barriers.

Cons of Apoplast Pathway

Blocked by Casparian strip in endodermis: less selective.

Symplast Pathway

Movement through the cells via the cytoplasm of cells interconnected by plasmodesmata.

Pros of Symplast Pathway

Selective: controlled by cellular processes.

Cons of Symplast Pathway

Slower due to crossing all membranes.

Root Nitrogen Fixation

Symbiosis of Rhizoids in the Fabaceae family contains nodules on roots and includes peas.

Rhizobia function

Nodules on roots that contain Rhizobia, which are bacteria that can break down N2 to ammonium, nitrite (N0), and nitrate (N0).

N2 in Soil usable or not usable to plants?

N2 is not usable by plants

N0 usable or not usable to plants?

A form of nitrogen usable by plants.

Rhizoids do what when present on roots?

When present on roots, can take N2 and convert it directly to N0 and give it to the plant.

Mycorrhizal relationships

Fungi form relationships with plants to exchange nutrients.

Mycorrhizal network

Contains mycelium beneath the soil.

Saprotrophic Nutrition

Fungi feed on non-living, dead or decaying organisms in the soil.

Enzyme expulsion by fungi- define this part of saprotrophic nutrition

Fungi expel enzymes into the soil and absorb nutrients after they are digested.

Heterotrophic

One organism relies on another for nutrients.

Fungi sugar acquisition

Fungi obtain sugars through a relationship with another plant like a tree.

Mycorrhizal net function

Surrounds a root, receives sugars from another plant, and provides minerals in return.

Mycorrhizal network communication

Connects plants and helps them communicate potential pest threats and run an ongoing nutrient sharing community.

Nutrient sharing

Mycorrhizal networks help share nutrients between plants.

what are Soil Horizons

Layers of soil with distinct characteristics.

O Horizon- define

Organic layer containing dead animals, dead plants, and decomposing materials.

A Horizon- define

Minerals and organic growth, good for plants; roots almost always reach here.

B Horizon

Rich in minerals, leached down, with not much organic material.

C Horizon

Parent material that develops into soil, consisting of broken down parent material.

R Horizon

Bedrock layer.

Soil Texture

Mixed percentages of sand, silt, or clay in the soil.

Sand

Large particles that allow water to fall through.

Silt

Particles measuring 0.05mm (small).

Clay

Particles measuring 0.02mm (super tiny) that hold water.

Water movement in soil define based on size

The size of particles dictates the ability of water to move through the soil. The larger the particle the more water loss.

Soil settling test

Mixing soil types in water to measure how quickly they settle.

Clay settling time

1-2 days.

Silt settling time

2 hours.

Sand settling time

1-2 minutes.

Mixed soil settles in what order

Clay on top, silt in between, sand on bottom.

Soil triangle test is used for what

Used to determine soil type based on percentages of clay, silt, and sand.

Water availability depends on?

Depends on soil type and impacts the water available to plants.

Clay water retention

Can “hold” lots of water, but due to tight compaction, making it less available to plants.

Loamyness- define

Increases water availability for plants by holding onto water and having less tightness in the space between particles due to multiple particle sizes.

Micronutrients

Essential elements only needed in small quantities.

Macro Nutrients

Nutrients required in larger quantities for plant growth.

Limiting Nutrients- define

Nutrients that if not available in sufficient amounts in the soil, will cause the plant's growth to suffer or be stunted.

Nitrogen (N)

A limiting nutrient obtained via the atmosphere.

Phosphorous (P)

A limiting nutrient obtained via the atmosphere.

Potassium (K)

A limiting nutrient obtained via the atmosphere.

Carbon

A nutrient obtained via the atmosphere.

Hydrogen

A nutrient obtained via the atmosphere.

Oxygen

A nutrient obtained via the atmosphere.

Calcium

A nutrient not classified as limiting.

Manganese

A nutrient not classified as limiting.

Sulfur

A nutrient not classified as limiting.

Soil pH, what is ideal?

6.2-7.3 is neutral to slight acidity preferred by most plants.

Nutrient availability dictates what about the soil?

Dictates the soil's pH level.

Toxins in soil what are they, what do they do to plants?

Substances in the soil that can negatively affect plant growth, including size and height of the plant, number of leaves, and size of leaves.

What are the 5 Soil formation factors?

Climate, living organisms, relief, parent material, and time.

Climate

Includes water (rain, rivers, streams, and snow) and temperature affecting soil formation.

Percolation- define

The process of water moving through soil, which can lead to leaching/ loosing of nutrients if excessive.

Leaching- define

Loss of nutrients from the soil due to excessive water.

Temperature effects soil in what ways?

High temperatures can cause rapid decomposition, while low temperatures may slow down decomposition.