ISA Study Guide 4th Edition: Chapter 1: Tree Biology

Meristem

The Meristem is the region where cell division and differentiation takes place to produce new specialized cells.

Differentiation

Differentiation is the process which alters the structure of cells to specialize them for a specific function.

Five Organs of the Tree

Leaves, Stems, Roots, Flowers, and Cones/Fruit

Primary Growth

Primary Growth occurs at root tips and shoot tips and increases the length/height of the root/stem.

Secondary Growth

Secondary Growth is growth that increases the thickness of the tree’s stems, branches and roots.

Apical Meristem

The area at the tips of roots and shoots where primary growth occurs. Growth in the apical meristem is responsible for leaf expansion and increases in the length of stems and roots.

Angiosperm

A plant that produces flowers and fruit which contains its seeds

Gymnosperm

A seed-producing plant that does not produce fruit or flower, generally seeds are exposed on the scales of cones

Buds

A bud contains the apical meristem. In temperate climates the apical meristem is protected by overlapping scales. Tropical trees and some temperate species lack this feature instead having “naked buds”.

Root Cap

Protects the apical meristem at the tip of roots

Vascular Cambium

One of two lateral meristems. The cambium is located just under the bark, it produces the vascular tissue of the tree comprised of the xylem, to the inside of the cambium, and the phloem, to the outside of the cambium.

Cork Cambium

One of two lateral meristems. The cork cambium produces outer tissues (periderm) and bark.

Cellulose

The structural component of the primary cell wall. Providing structure to cells

Lignin

Lignin forms a matrix in which long chains of cellulose, microfibrils, are embedded, reinforcing the cell wall. This provides additional rigidity to the cell walls of the cells that form the wood

Xylem

Vascular tissue produced by the vascular cambium also known as secondary xylem or wood. Comprised of both dead and living cells, the cell walls of the dead cells contain cellulose and lignin providing the strength for the wood.

Functions of the Xylem

1. Conduction of water and dissolved elements (sap)

2. Mechanical Support for the tree

3. Storage of carbohydrate (starch) reserves

4. Defence against the spread of dysfunction, disease and decay

Tracheids

Elongated, close-ended, dead cells with pointed ends and thickened walls. Responsible for water conduction and mechanical support

Parenchyma Cells

Living cells responsible for storing carbohydrates and defending against decay.

Wood of Gymnosperms

Composed mostly of tracheids and few parenchyma cells

Eudicotyledon(Eudicot)

Angiosperm with 2 seed leaves

Monocotyledon(Monocot)

Angiosperm with 1 seed leaf

Vessels

Primary conducting elements in angiosperms. Xylem vessels can be thought of as stacks of dead, open-ended, hollow cells forming long tubes.

The wood of eudicotyledon

Eudicotyledon trees are primarily comprised of vessel elements, fibers and parenchyma cells. In some species tracheids may also be present.

Differences in structure between angiosperms and gymnosperms

Parenchyma cells are more abundant in angiosperm trees

Ring porous

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

Diffuse porous

Trees that form vessels of uniform size throughout the growing season

Growth Rings

Rings resulting from the seasonal xylem production, this forms rings due to the relative size and density of the vascular tissues change throughout the growing season. As the season progresses cells become smaller in diameter.

Earlywood

Wood produced early in the season

Latewood

Wood produced late in the season

Non-Porous Wood

Conifers do not have vessels thus are considered to have non-porous wood

Sapwood

Xylem that conducts water containing many living parenchyma cells.

Heartwood

Old layers of sapwood that are deeper within the tree cease to conduct water and cells that made up the sapwood die turning the sapwood into Heartwood. Heartwood contributes to mechanical support of the tree and resist disease.

Photosynthates

The sugar products of photosynthesis, the building blocks for many other compounds required by the plant

Rays

Radial transport of photosynthates, extend across the xylem and phloem. Moves carbohydrates into and out of sapwood. Formed of parenchyma cells thus also stores carbohydrates and assist in resisting decay.

Bark

Outer layer of the tree, formed of old phloem that is crushed and cell walls used to reinforce bark. Moderates temperature inside stem, reduces water loss and protects against damage.

Lenticels

Small openings in the bark that allow gas exchange.

Apical Buds/Terminal Buds

Buds at the end of a twig, containing the apical meristem

Axillary Buds

Buds that occur along the stem, still containing a meristematic zone but often dormant.

Apical Dominance

The process of the terminal bud chemically inhibiting the growth and development of laterals on the same stem.

Adventitious buds

Buds produced along the stem where primary meristems aren’t normally found. They may be activated by the loss of the apical meristem.

Latent Buds/ Epicormic shoots

Buds that are suppressed beneath the bark unless growth is triggered by light or tree damage. The shoots produced by latent buds are called epicormic shoots.

Node

Enlarged portion of a twig where leaves and buds develop.

Internode

The area between nodes, can be used to measure annual growth by measuring the length between the terminal bud scars and leaf scars.

Branch Collar

A shoulder or bulge around the branch base as a result of annual growth at the junction of the branch to the stem.

Branch Union

Junction between the stem and branch.

Branch Bark Ridge

A ridge of bark at the top of the branch collar resulting from specialized wood that is particularly dense and features a whirled grain.

Included Bark

Bark that has become embedded into the junction weakening the attachment.

Chlorophyll

Green primary leaf pigment that absorbs sunlight

Chloroplasts

Cell components that contain chlorophyll

Photosynthesis

The process through which sunlight is converted to chemical energy in the form of carbohydrates.

Transpiration

The second function of the leaf, transpiration is the controlled loss of water through the stomata of the leaf, cooling the surface of the leaf.

Cuticle

Waxy outer layer of the leaf that minimizes desiccation(drying out) of the leaf

Stomata

Small openings generally on the underside of the leaf that regulate transpiration using guard cells to adjust openings and thus the amount of carbon dioxide absorbed and water released.

Guard Cells

Cells responsible for opening and closing stomata in response to environmental conditions such as light, temperature, and humidity.

Leaf Veins

Bundles of vascular tissue made up of xylem and phloem.

Deciduous

Trees that shed there leaves periodically, generally annually. Typically this is in response to environmental changes such as day length, temperature, and/or rainfall.

Evergreen

Trees that do not shed leaves.

Abscission Zone

Formed at the base of the petiole to enable leaf drop and protect the region of the stem from which the leaf has fallen

Petiole

Leaf stalk

Anthocyanins

Red/purple pigments that become prominent in autumn when chlorophyll breaks down that protect the leaf cells from UV radiation while sugars and amino acids are absorbed by the tree.

Carotenoids

Yellow/orange/red pigments that become prominent in autumn when chlorophyll breaks down that protect the leaf cells from UV radiation while sugars and amino acids are absorbed by the tree.

Purpose of the roots

1. Anchorage

2. Storage

3. Absorption

4. Conduction

Absorbing Roots

Small, fibrous primary tissues growing at the ends of and along the main woody roots, mostly found in the top 30cm of soil. They utilize root hairs to aid in water and mineral uptake as well as a primary meristematic zone.

Lateral roots

Roots that grow horizontally out from the trunk.

Sinker Roots

Roots that grow vertically downward off the lateral roots for added anchorage and better access to deeper water reserves

Taproot

Root that grows downward on a young tree, usually replaced with root expansion or diverted from downward growth

Root Crown

Where roots meet the main stem, beginning the “zone of rapid taper” where roots quickly narrow and spread, spreading as far as 2-3 times the trees canopy.

Mycorrhizae

Fungal roots resulting from the symbiotic relationship between fungus in the soil and the tree’s root system. The fungus feed on tree roots and in return the fungus aids in the absorption of water and essential mineral elements.

Symbiosis

A mutually beneficial relationship between two organisms.

Respiration

The process by which the carbohydrates are converted in a controlled manner into energy; it is independent of light.

Energy Balance

It is essential that photosynthesis exceeds respiration to ensure that the plant is producing more energy than it is using. If this is not the case the tree is forced to use stored carbohydrates.

Cell Turgor

The pressure of water inside the guard cells.

Osmosis

The movement of water from an area of high concentration to an area of low concentration. Minerals in the ground reduce the waters concentration, when too many minerals(ex. over fertilization) are present in the soil it can lower concentration enough that water flows from the roots to the soil damaging the tree.

Movement of carbohydrates in the Phloem

The movement of carbohydrates through the phloem is an active process that requires energy. The phloem moves carbs from source to sink. Leaves are the source as they produce carbs. The sink is any area throughout the tree requiring energy. Most photosynthates are utilized close to where they are produced but can move anywhere through the phloem.

Axial Transport

Transport systems that move along stems

Radial Transport

Transport systems that move carbs between xylem and phloem

Plant growth regulators/ Plant hormones

Chemical messengers that regulate plant growth and development.

Major Hormone Groups

Auxins, gibberellins, cytokinins , ethylene, and abscisic acid

Auxins

Plant growth regulators linked to numerous functions of the tree. Despite being produced primarily at shoot tips it has been shown that they have a large impact on root growth and when additional auxins are supplemented to a tree it can stimulate root growth. As well as this crown pruning can reduce the roots ability to regrow after damage due to the reduction in auxin production.

Cytokinins

A plant growth regulator produced in the roots which is essential to shoot initiation and growth.

Tropism

The directional growth of a tree in response to environmental factors such as light or gravity.

Geotropism

Growth in reaction to gravity.

Phototropism

Growth in reaction to light.

Decurrent Tree

A tree with a rounded structure as a result of lateral shoots overtaking leaders at the start of the growing season due to auxin production being “reset” at the start of the new growing season. Typically seen in deciduous trees.

Excurrent Trees

A tree with a straight, upright shape as a result of strong apical dominance. Typically seen in conifers.

Compartmentalization

Compartmentalization is the process by which trees seal wounds to prevent pests, rot and disease from entering the tree at the site of a wound.