Tree Biology – Roots, Shoots & Leaves

Tree Stewards Training

Nick Bomber

ISA Certified Arborist ISA Certified Tree Climber Specialist & Evaluator TCIA Certified Tree Care Professional 10 years experience in “Greens Industry” Operations Manager for SavATree/SavALawn

Introduction

Learn the structures and functions of the bud’s, leaves, wood and roots of a tree.

Understand the interaction of structure and function in tree biology.

Learn the basic composition of a tree’s vascular system and understand how water and carbohydrates are transported within this system.

First Half Agenda

Key Terminology

Key Terms!

Protoplasm

A complex colorless substance forming the living contents of a cell.

Chloroplast

Specialized organelle found in some cells and is the site of photosynthesis.

Abscission Zone

Area at the base of the petiole where cellular breakdown leads to leaf drop.

Absorbing Roots

Fine, fibrous roots that take up water and minerals; most of them are within the top 12 inches of soil.

Adventitious buds

Bud that arises from a place other than a leaf axil.

Anthocyanins

Red, purple, or blue pigments; responsible for those colors in some parts of trees and other plants.

Antitranspirant

Substance sprayed on plants to reduce water loss through the foliage.

Apical bud

Terminal bud on a stem.

Apical dominance

Condition in which the terminal bud inhibits the growth and development of lateral buds on the same stem.

Apical Meristem

The growing points at the tips of shoots.

Auxin

Plant hormone or substance that promotes or regulates the growth and development of plants; it is produced at sites where cells are dividing, primarily in the shoot tips.

Axial Transport

Movement of water, minerals, or photosynthate longitudinally within a tree.

Axillary bud

Bud in the axil of a leaf; lateral bud.

Branch Bark Ridge

Top area of a tree’s crotch where the growth and development of the two adjoining limbs push the bark into a ridge.

Branch collar

Area where a branch joins another branch or trunk created by the overlapping xylem tissues.

Buds

Small lateral or terminal bulge on the stem of plant that may develop into a flower or shoot; undeveloped flower or shoot.

Cambium

Layers of cells that give rise to the phloem and xylem and allow for the diameter to increase.

Carbohydrate

Compound, combining carbon and water, produced by plants during photosynthesis.

Carotenoids

A yellow, orange, or red pigment responsible for those colors in some parts of trees and other plants.

Chlorophyll

Green pigment of plants, found in chloroplasts; it captures the energy of the sun and is essential in photosynthesis.

CODIT

Compartmentalization Of Decay In Trees.

Companion cell

Companion cells provide the energy for the tube cells.

Compartmentalization

Natural process of defense in trees by which they wall off decay in the wood.

Cork cambium

Meristematic tissue from which cork and bark develop to the outside.

Cuticle

Waxy layer outside the epidermis of a leaf.

Cytokinin

Plant hormone involved in cell division.

Bonus Question !!!!!!!!!!!!!

Why do leaves change color?

In the fall, the concentration of chlorophyll decreases in concentration to reveal other pigments. These other pigments have been present throughout the year contributing to photosynthesis but their appearance was masked by the large concentration of chlorophyll pigments.

Deciduous

Tree or other plant that loses its leaves sometime during the year and stays leafless generally during the cold season.

Decurrent

Rounded or spreading growth habit of crown of tree.

Differentiation

Process in the development of cells in which they become specialized for various functions.

Diffuse porous

Pattern of wood development in which the vessels are distributed evenly throughout the annual ring.

Dormant

State of reduced physiological activity in the organs of a plant.

Epicormic

Arising from latent or adventitious buds.

Evergreen

Tree or plant that keeps its needles or leaves year round; this means for more than one growing season.

Excurrent

tree trunk continuous to top; many small lateral branches, slender silhouette.

Fiber

Elongated, tapering, thick-walled cell that provides strength.

Geotropism

Plant growth produced as a response to the force of gravity; it can be positive as in the roots, or negative as in the trunk.

Growth Rings

Rings of annual xylem visible in a cross section of the trunk of some trees.

Guard cells

Pair of cells that regulate the opening and closing of stomate due to a change in water content.

Gymnosperm

Plant with seeds exposed.

Heartwood

Inner, nonfunctional xylem tissues that provide structural resistance to the trunk.

Included bark

Bark that becomes embedded in a crotch between branch and trunk or between codominant stems and causes a weak structure.

Internode

The region of the stem between two successive nodes.

Lateral roots

Side-branching root that grows horizontally.

Lenticel

Opening in the bark the permits the exchange of gases.

Meristem

Growing point in a stem.

Mycorrhizae

A symbiotic association between a fungus and the roots of a plant.

Node

Slightly enlarged portion of stem where leaves and buds arise.

Osmosis

Diffusion of water through a semi-permeable membrane from a region of higher water potential to a region of lower water potential.

Parenchyma cells

Thin-walled, living cells essential in photosynthesis and storage.

Petiole

The stalk or support axis of a leaf.

Phloem

Plant vascular tissue that conducts photosynthate; located to the inside of the bark.

Photosynthate

General term for the products of photosynthesis.

Photosynthesis

The process in green plants by which light energy is used to form organic compounds from water and carbon dioxide.

Phototropism

Influence of light on the direction of plant growth.

Radial transport

Movement of substances in a tree perpendicular to the longitudinal axis of the tree.

Ray

Tissues that extend radially across the xylem and phloem of a tree.

Reaction zone

A natural boundary formed by a tree to separate wood infected by disease organisms from healthy wood; important in the process of compartmentalization.

Respiration

Process by which carbohydrates are converted into energy by using oxygen.

Ring porous

Tree that form wide vessels early in the growing season and narrower vessels later in the season.

Sapwood

Outer wood that actively transports water and minerals.

Sieve cells

Long, slender phloem cells.

Sinker roots

Downward-growing roots that take up water and minerals; most are in the top 12 inches of soil.

Source

Plant part that produces carbohydrates; mature leaves are sources.

Stomata

Small pores between two guard cells on leaves and other green plant parts through which gases are exchanged.

Bonus Question !!!!!!!!!!!!!!!!!!

Why do leaves fall from the tree?

Hormones cause physical changes to cells located between the petiole and stem in an area called the abscission zone. There is controlled cell death in this region allowing the tree to shed the leaf and to protect the exposed stem tissue from desiccation and infection.

Symbiosis

A mutually beneficial association of two different types of living organisms.

Tap root

Central, vertical root that grows right below the trunk and is often choked off by development of other roots.

Terminal bud

A bud at the end of a twig or shoot.

Tracheid

Elongated, tapering xylem cell, adapted for support.

Transpiration

Water vapor loss through the stomata of leaves.

Tropism

Growth movement or variation of a plant as a response to an external stimulus such as light or gravity.

Vessels

Stacked, tube like, water-conducting cells in the xylem.

10 minute break!

Basic Structure: Cells and Tissues

Similarities: Plant and Animal Cells – Both cells have cytoplasm which is basically "cell guts."

– Both cells have an outer cell membrane which separates the external environment from the cell's cytoplasm.

– Both cells have a nucleus containing DNA which controls the activities of the cell.

– Both cells have numerous organelles called mitochondria to convert sugar into a more useful energy molecule.

How does a tree grow?

A tree grows two ways: branches and roots grow longer from buds and the trunk and branches grow wider thanks to an incredibly thin layer of cells located just under the bark called the vascular cambium.

Tissue that has the ability to divide and grow into new structures is called meristematic tissue.

Differentiation of cell basically means the cell gets a job.

Xylem and Phloem

Xylem and phloem tissues are produced by meristematic cambium cells located in a layer just inside the bark of trees and shrubs.

These two tissues extend from the leaves to the roots, and are vital conduits for water and nutrient transport. In a sense, they are to plants what veins and arteries are to animals.

The Xylem has four primary functions:– Conduction of water and dissolved minerals– Support of the weight of the tree– Storage of carbohydrates– Defense against the spread of disease and decay

Tracheid are long and relatively narrow, and transport materials from the roots upward.

Xylem

Phloem

Responsible for the movement of sugars, produced in the leaves, to other plant parts.

Phloem transport requires energy.

The two most common cells in the phloem are the companion cells and sieve cells.

Stems

Be familiar with the following structures, you should know not only where each is located, but you should also be familiar with the function of each structure.

Leaves

FUNCTION OF LEAVES– Leaves are the solar energy and CO2 collectors of

plants.

Two words: photosynthesis & transpiration.

Photosynthesis

Physiological process in which carbon dioxide and water are combined to produce sugar.

The process begins when sunlight strikes chlorophyll, a green pigment, inside of the chloroplasts.

A byproduct of this reaction, oxygen, will diffuse out of the leaf.

Transpiration

A very small amount of the water absorb by the roots actually goes into photosynthesis.

95% of the water that enters the roots travels up through the xylem and out the stomates.

Transpiration can also be thought of as “tree sweating,” this will cool off the tree.

Roots

Serve Four Primary Functions:– Anchorage

– Storage

– Absorption

– Conduction

How do roots grow?

The tip of very young roots are protected by a collection of cells called the root cap.

Behind the root cap is the root apical meristem which is rapidly dividing to produce cells which move forward to become the root cap.

After increasing in size, these cells now undergo differentiation (they get jobs) into xylem, phloem and root hairs.

Tree Physiology- Respiration

Unlike photosynthesis, which is seasonal in most climates, at least some respiration occurs at all times (even during the dormant season).

Respiration is the oxidization of carbohydrates to provide energy to keep cells alive and to fuel growth.

Without a surplus of carbohydrates, tree vigor declines and eventually death occurs.

Excurrent and Decurrent Trees

All tree have apical dominance. Trees that have strong apical control develop an excurrent form while trees with weak apical control develop a decurrent form.

In excurrent trees, the lateral branches remain inferior to the central leader. The central leader is able to maintain this condition because it maintains strong apical control and continually suppresses the development of lateral branches.

In decurrent trees, the central leader is unable to exert strong apical control and the lateral branches begin to grow just as fast as the central leader.

Excurrent or Decurrent

Plant Hormones

Auxins produced in the terminal buds suppress the growth of side buds and stimulates root growth. They also affect cell elongation (tropism), apical dominance, and fruit drop or retention.

Gibberellins affect the rate of cell division, flowering, increase in size of leaves and fruits.

Cytokinins promote cell division, and influence cell differentiation and aging of leaves.

Abscisic acid is considered the “stress” hormone. It inhibits the effects of other hormones to reduce growth during times of plant stress.

Understanding hormones is key to proper pruning

Reduction pruning releases the apical dominance caused by auxins from the terminal bud.– This allows side shoots to develop and the branch

becomes bushier.

Thinning cuts remove a branch back to the branch crotch.– This type of cut opens the plant to more light.

A System of Defense

Compartmentalization is a process by which trees limit the spread of discoloration and decay.

After a tree has been wounded, reactions are triggered that cause the tree to form boundaries around the wounded area.

CODIT – 4 walls

Wall 1 is formed when the tree responds to wounding by “plugging” the upper and lower vascular system to limit vertical spread of decay.

Wall 2 is formed by the last cells of the growth ring, limiting inward spread.

Wall 3 is composed of ray cells that compartmentalize decay by limiting lateral spread.

Wall 4 Is the strongest wall and is the new growth ring that forms after injury.

Thank you!