Unit 4: Plant Growth and Development (Lesson 14)

Plant Hormones (1)

The chemicals are a substance produced in one part of an organism that has a target elsewhere in the organism > These chemicals in plants play a central role in controlling the way plants grow and develop > They regulate the growth of the individual parts and integrate them to produce the forms we recognize as plants 1. Auxins

Insects

The frequency, duration, and extent of these little guys are predicted to increase with climate exchange > Example: mountain pine beetle lays its eggs in the bark of pine trees in western Canada and the larvae burrow onto the tree, creating holes that eventually lead to the death of the tree

Soil pH

The measure of the acidity or alkalinity of soil > All plants have a different pH preferences > Mosses (grow in acidic soils) -- The pH of soil directly affects the availability of essential nutrients for plant growth > Acidic: minerals such as zinc, aluminum, manganese, and copper are soluble and available for plant uptake > Too acidic: these minerals can be absorbed in excessive quantities, becoming toxic -- Alkaline soil may contain a higher quantity of bicarbonate ions and can affect optimum growth in plants by interfering with the normal uptake of other ions -- Common Range of Soil pH: 4 to 8 > Optimal availability of plant nutrients for most crops is: 6.5 to 7.0 pH

Hormones

A chemical in the body that controls and directs activity in other cells

Auxins (2)

A class of plant hormones produced in the meristem (growth area) of plants > They are responsible for cell elongation, a process that is required before differentiation of a cell can occur > These support elongation by promoting the intake of water, which increases elasticity of the cell as it copes with the greater amount of water taken in -- Two Main Functions: (tissue growth & formation) 1. Role in Root & Shoot Growth 2. Role in Bud Formation

Soil (7)

A complex living community that is vital to the growth and development of plants > This and organisms that live in, determine the nutrient and water availability for plants -- Organisms living in Soil: decompose organic matter, cycle nutrients, enhance soil structure, and control the populations of other organisms - beneficial and harmful --> In turn, plant residues and the by-products of growing roots feed soil organisms 1. Healthy Soil Functions 2. Soil Structure 3. Soil Formation 4. Humus 5. Soil pH 6. Soil Compaction 7. Careers in Soil Science

Nitrogen (N)

A component of proteins, amino acids, nucleic acids, and chlorophyll -- D: light green to yellow appearance of leaves (*chlorosis*), especially to older leaves; stunted growth; poor fruit development -- E: dark green foliage which may be susceptible to lodging, drought, disease, and insect invasion. Fruit and seed crops may fail to yield -- * The picture shows the plant with pale green leaves with a yellow appearance, a sign of deficiency in this micronutrient (chlorosis)

Fertilizers (2)

A fertilizer is any material, organic or inorganic, natural or synthetic, that provides the necessary nutrients for plant growth and optimal yield > They can be applied to soil before seeds are sown at the time of planting, or while the plants are growing > They can also be applied while transporting vegetables, flowers, trees, shrubs, and other types of plants -- Almost all contain the three essential nutrients (N, P, and K) and often show in rations such as: 10N:5P:5K 1. Organic Fertilizers 2. Inorganic Fertilizers

Dought

A period of low rain fall and the absence of sufficient water-fall

Nitrogen Fixing in Agriculture

Composed by rhizobia bacteria, this process is of great importance to agriculture: 1. Legumes (peas/lentils/beans/soybeans) help feed the meat-producing animals of the world as well as humans 2. Legumes also grow well in poor soils where there is not enough nitrogen to support other types of plants 3. Legumes are used to enrich soils for uptake by later crops - after harvest, the legume roots are left in the soil to decay, releasing organic nitrogen compounds for next generations

Phosphorus (P)

D: leaves may develop purpose coloration (*anthocyanosis*): stunted plant growth; delayed plant development -- E: may cause micronutrient deficiencies, especially iron or zinc, resulting in chlorosis or *necrosis* (death)

Potassium (K)

D: older leaves turn yellow initially around margins (chlorosis) and die (necrosis); irregular fruit development -- E: causes deficiencies in magnesium and possibly calcium, resulting in chlorosis and possible stunted growth

Symptoms of Primary Macronutrient Deficiency or Excess (4)

Deficiency = D | Excess = E | 1. Nitrogen (N) 2. Phosphorus (P) 3. Potassium (K) 4. Fertilizers

Plant Adaptations

Deforestation and climate change are occurring so quickly that plants now have little or no time to adapt to their altered environments

Nitrogen Fixing in Farming

Farmers take advantages of this natural fertilization by plating a leguminous crop one season, followed by a non-leguminous crop in the same field the next season > This process is known as *crop rotation* and reduces the need for commercial fertilizers --> Overall: saving money and helps prevent the problems brought by excessive use of commercial fertilizers

Importance of Plant Growth (1)

In Canada, harvesting of wood through the forestry industry is a major economic force (particularly the boreal and coastal forests of the north and West) > There are regulations on clear-cutting to reduce the impacts of it > Tropical forests face the threat of unregulated and illegal logging; 1. Climate Change

Soil Structure

Is made of three components: minerals, organic matter (plants/animal), and the organisms that live in its upper layers > It is formed slowly as rock (the parent material) erodes into tiny pieces near the earth's surface by the natural weathering action of wind water, glaciers, and temperature changes > These weathering agents break rock into finer and finer grains & are eventually deposited on the ground in layers > Decaying organic matter than mixes with the inorganic material (rock particles, minerals, and water) to form this -- Many different types, each with their own unique characteristics such as colour, texture, structure, and mineral content > The depth also varies > The types of this organic matter in an area helps determine what plants can grow there

Organic Fertilizers

Made from natural materials such as manure, crop residues, household waste, compost, and woodland litter -- Advantage(s): 1. Compared to mineral fertilizers, they are usually found on the farm naturally and available at low costs 2. Increased organic matter in the soil, reduced erosion, and better water retention 3. Lasts years after first application/use of it (+ increasing yields) -- Disadvantage(s): 1. Generally slower acting than inorganic fertilizers

Soil Formation

Micro-organisms in the soil convert the decaying plant material into organic molecules that can be used by other organisms -- Some are simple molecules: sugars, amino acids, and cellulose - which are readily consumed by many organisms > For this reason, they do not remain in the soil very long -- Other complex molecules from plants, such as *resins* and *waxes*, are more difficult for soil organisms to break down and, eventually residues help form humus

Role in Bud Formation

Most plants have lateral buds located at nodes (where leaves attach to the stem) > Buds are embryonic meristems maintained in a dormant state > The presence of auxins, like IAA, in lateral areas of the plant (in b/t the root and shoot tip can prevent lateral growth --> Remove the apical bud = the removal of IAA --> With auxin concentration being much lower, later buds can now grow (this is why you cut the top off some plants when the lower parts suddenly start growing new branches) -- Auxins are now responsible for leaves falling off deciduous trees in autumn > As days grow colder and the rate of photosynthesis drop: the auxin levels decline --> A lack of auxin in the lateral areas of the stem results in the formation of a separation layer (*abscission*) where the leaf petiole joins the stem --> As a result, the abscission weakens the leaf's connection with the plant and soon causes it to fall off

Rhizobial Bacteria

Nitrogen is one of the most important chemical elements for plants > One source of nitrogen in the soil comes from the air: the atmosphere contains 78% of nitrogen in the form of N2 (nitrogen gas) --> Plants cant use his form of nitrogen so the plants use their ability to form a *symbiotic* relationship with a type of *r-bacteria* --> This converts N2 into NH4+ (ammonia) which plants can use ------ The bacteria live inside the root hairs of the plant and naturally produce ammonia in a process called: *nitrogen fixing*(1)

Soil Compaction

Occurs when soil particles are pressed together, reducing the space between them: *pore space* > Heavily compacted soils such as those found in urban centres contain few pores, and have a reduced rate of both water infiltration and drainage from the compacted layer --> This occurs because large pores are the most effective for water to move through the soil --> In addition, the exchange of gases are slower in compact soils, cause and increase in the problems related to poor aeration > Plants have a hard time growing in compacted soil because their roots must exert greater force to penetrate the compacted layer

Role in Root and Shoot Growth

One of the most common auxins is *indole acetic acid (IAA)*: this affects the root and shoot tips of the plant > Depending on its location, IAA promotes or inhibits growth --> An effect of adjusting the level of IAA is to allow the plant to bend forward or away from light (*phototropism*) --> This happens because IAA are found in the shoot tip and are broken down by exposure to sunlight > The part (or side) of the shoot tip exposed to direct sunlight will have less auxin while the part (or side) in the shade will have more --> The extra auxin present on the shaded side promotes more cell division and elongation, which makes the shaded side longer (causing the plant to bend toward the sunlight) * Note: Helps plants seek sunlight when competing in the shadows of other plants

Eutrophication

Over-fertilization of rivers, lakes, and acid rain

Careers in Soil Science

Pedologist: a scientist who studies soil > Geography, renewable resources, or earth sciences > Major areas of study: biology, soil chemistry, soil physics, sort fertility, soil classification, mineralogy and conservation, soil contamination and remediation, land classification, and forest soil

Healthy Soil Functions

Some functions in this healthy s-ecosystem: 1. Decomposing organic matter into humus 2. Retaining water 3. Retaining nitrogen and other nutrients 4. Making retained nutrients available to the plant 5. Binding soil particles together for optimal structure 6. Protecting roots from disease and parasites 7. Producing hormones that help plants grow

Nitrogen Fixing (3)

The plant forms nodules (lumps) around where the bacteria are living > These nodules are the sources for the ammonia that get taken up by the plants roots > *Symbiotic Relationship*: the plants benefit from obtaining the nitrogen for growth - while the bacteria benefit from being protected inside the plant's roots and obtaining some of the food produced by the plant * Note: the majority of nitrogen-fixing plants on earth are legumes like beans, clovers, and peas & some trees, like the alder 1. Agriculture 2. Farming 3. Eutrophication

Humus

The result of successive steps in the decomposition of organic matter > This term is food but known by gardeners to mean the organic material that makes soil brownish, but not all of that is this material -- It is made up of the non-cellular parts of organisms after they decompose > During decomposition, everything else in the cell breaks down and gets recycled into other organisms, leaving this in the soil --> In nature, this accumulates in soil because it lasts for 100's-1000's of years ------ Enhances plant growth > Some function as natural plant hormones (auxins/gibberellins) > Capable of improving seed germination, root initiation, and uptake of plant nutrients > Other substances help create the physical conditions that keep the soil moist, cook, and capable of supporting a diversity of soil organisms

Conditions for Plant Growth (3)

Three conditions must be met for plant growth to flourish: 1. Soil 2. Nutrients 3. Rhizobia (type of bacteria)

Inorganic (Mineral) Fertilizers

Traditionally mined from mineral deposits such as lime (calcium), potash (potassium), or phosphate rock (phosphorus) > Can be manufactured through chemical processes, often using fossil fuels as the source, to produce nitrogen fertilizer -- Advantages(s): 1. They make nutrients rapidly available to plants and that the exact number of a given element can be measured before feeding plants -- Disadvantages(s): 1. Nutrients are released very quickly in the soil after application which means they may run off or leach out of the soil during rain or irrigation to pollute local streams 2. They can also rapidly build up in the soil, forming salts that can eventually become toxic to plants

Climate Change (1)

Two of the largest outbreaks on forests are *insects* and *fires* > Fire is a natural and critical part of healthy forest ecosystems in Canada but the fires are becoming more large-scale --> Climate warms and the direr conditions create even more severe droughts, which make fires more likely 1. Insects

Nutrients (1)

Unlike animals - which obtain their nutrition from the food they eat: plants obtain their nutrition from the soil and atmosphere > Sunlight: main energy source, plants are capable of making all the organic macromolecules they need by modifying the sugars they form through photosynthesis > Several minerals are needed for growth: which enter from the root system 1. Essential Plant Nutrients: elements necessary for plants to complete their life cycle --> Each of these nutrients has a critical function in plants, and is required in varying amounts of plant tissue ------ Macronutrients: required in the largest amount of nutrients - *nitrogen, phosphorus, potassium, calcium, magnesium, and sulphur* Micronutrients: required in smaller amounts - *iron, copper, manganese, zinc, boron, molybdenum, and chlorine* -- Nutrient deficiency(ND) or toxicity symptoms often differ among species and varieties of plants > (ND): Occurs when a nutrient is not present in sufficient quantity to meet the needs of the growing plant > Toxicity occurs when a nutrient is present in excess quantity 1. Symptoms of Primary Macronutrient Deficiency or Excess