UNIT 3 PLANTS

Plants are living things that are made up of cells. They need air, water, soil, and sunlight to live. They cannot move from place to place, but their leaves move to catch the sun and their roots move towards water. Their seeds can be carried by animals or blown by the wind. We get food from all different parts of the plant: flowers, fruits, vegetables, seeds, nuts, stems, and leaves. Grass gives us a cool, soft place to walk. Some plants give us medicine, and trees are used to make paper and furniture.

Plants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants is known as botany. As of 2010, botanists have identified more than 315,000 species of plants, of which 281,821 are flowering, 12,000 are ferns and fern allies, and 16,236 are bryophytes.  Green plants, sometimes called Viridiplantae, obtain most of their energy from sunlight via photosynthesis. This process uses chlorophyll contained in chloroplasts, which gives plants their green color.

Plants are alive, just like people and animals. How do we know this? Living things all do certain things:

They grow and die.

They need energy, nutrients, air, and water.

They produce young.

They are made up of cells.

They react to what's around them.

Importance

The study of plant uses by people is termed economic botany or ethnobotany; some consider economic botany to focus on modern cultivated plants, while ethnobotany focuses on indigenous plants cultivated and used by native peoples. Human cultivation of plants is part of agriculture, which is the basis of human civilization. Plant agriculture is subdivided into agronomy, horticulture and forestry.

Food

Much of human nutrition depends on land plants, either directly or indirectly.

Human nutrition depends to a large extent on cereals, especially maize (or corn), wheat and rice. Other staple crops include potato, cassava, and legumes. Human food also includes vegetables, spices, and certain fruits, nuts, herbs, and edible flowers.

Beverages produced from plants include coffee, tea, wine, beer and alcohol.

Sugar is obtained mainly from sugar cane and sugar beet.

Cooking oils and margarine come from maize, soybean, rapeseed, safflower, sunflower, olive and others.

Food additives include gum arabic, guar gum, locust bean gum, starch and pectin.

Livestock animals including cows, pigs, sheep, and goats are all herbivores; and feed primarily or entirely on cereal plants, particularly grasses.

Nonfood products

Wood is used for buildings, furniture, paper, cardboard, musical instruments and sports equipment. Cloth is often made from cotton, flax or synthetic fibers derived from cellulose, such as rayon and acetate. Renewable fuels from plants include firewood, peat and many other biofuels. Coal and petroleum are fossil fuels derived from plants. Medicines derived from plants include aspirin, taxol, morphine, quinine, reserpine, colchicine, digitalis and vincristine. There are hundreds of herbal supplements such as ginkgo, Echinacea, feverfew, and Saint John's wort. Pesticides derived from plants include nicotine, rotenone, strychnine and pyrethrins. Drugs obtained from plants include opium, cocaine and marijuana. Poisons from plants include ricin, hemlock and curare. Plants are the source of many natural products such as fibers, essential oils, natural dyes, pigments, waxes, tannins, latex, gums, resins, alkaloids, amber and cork. Products derived from plants include soaps, paints, shampoos, perfumes, cosmetics, turpentine, rubber, varnish, lubricants, linoleum, plastics, inks, chewing gum and hemp rope. Plants are also a primary source of basic chemicals for the industrial synthesis of a vast array of organic chemicals. These chemicals are used in a vast variety of studies and experiments.

Aesthetic uses

Thousands of plant species are cultivated for aesthetic purposes as well as to provide shade, modify temperatures, reduce wind, abate noise, provide privacy, and prevent soil erosion. People use cut flowers, dried flowers and houseplants indoors or in greenhouses. In outdoor gardens, lawn grasses, shade trees, ornamental trees, shrubs, vines, herbaceous perennials and bedding plants are used. Images of plants are often used in art, architecture, humor, language, and photography and on textiles, money, stamps, flags and coats of arms. Living plant art forms include topiary, bonsai, ikebana and espalier. Ornamental plants have sometimes changed the course of history, as in tulipomania. Plants are the basis of a multi-billion dollar per year tourism industry which includes travel to arboretums, botanical gardens, historic gardens, national parks, tulip festivals, rainforests, forests with colorful autumn leaves and the National Cherry Blossom Festival. Venus Flytrap, sensitive plant and resurrection plant are examples of plants sold as novelties.

Scientific and cultural uses

Tree rings are an important method of dating in archeology and serve as a record of past climates. Basic biological research has often been done with plants, such as the pea plants used to derive Gregor Mendel's laws of genetics. Space stations or space colonies may one day rely on plants for life support. Plants are used as national and state emblems, including state trees and state flowers. Ancient trees are revered and many are famous. Numerous world records are held by plants. Plants are often used as memorials, gifts and to mark special occasions such as births, deaths, weddings and holidays. Plants figure prominently in mythology, religion and literature. The field of ethnobotany studies plant use by indigenous cultures which helps to conserve endangered species as well as discover new medicinal plants. Gardening is the most popular leisure activity in the U.S. Working with plants or horticulture therapy is beneficial for rehabilitating people with disabilities. Certain plants contain psychotropic chemicals which are extracted and ingested, including tobacco, cannabis (marijuana), and opium.

Negative effects

Weeds are plants that grow where people do not want them. People have spread plants beyond their native ranges and some of these introduced plants become invasive, damaging existing ecosystems by displacing native species. Invasive plants cause billions of dollars in crop losses annually by displacing crop plants, they increase the cost of production and the use of chemical means to control them affects the environment.

Plants may cause harm to people and animals. Plants that produce windblown pollen invoke allergic reactions in people who suffer from hay fever. A wide variety of plants are poisonous to people and/or animals. Toxalbumins are plant poisons fatal to most mammals and act as a serious deterrent to consumption. Several plants cause skin irritations when touched, such as poison ivy. Certain plants contain psychotropic chemicals, which are extracted and ingested or smoked, including tobacco, cannabis (marijuana), cocaine and opium. Smoking causes damage to health or even death, while some drugs may also be harmful or fatal to people.[29][30] Both illegal and legal drugs derived from plants may have negative effects on the economy, affecting worker productivity and law enforcement costs.[31][32] Some plants cause allergic reactions in people and animals when ingested, while other plants cause food intolerances that negatively affect health

The Plant Kingdom

The Plant Kingdom is a way to classify (or organize) plants. They are divided into groups based on the traits they have in common. Scientists change the way plants are classified from time to time, when they discover new types of plants or learn new things about plants.

The two main groups are vascular plants (plants that use stems and veins to transport food and water), and non-vascular plants (plants with no roots, stems, or leaves).

Vascular plants can divided into smaller groups, one of which is seed plants. This group includes flowering and non-flowering plants.

Flowering plants include monocots (one seed leaf) and dicots (two seed leaves). The non-flowering plants can also be divided into several groups, including cycads, conifers, and ginkgo.

About Non-Flowering Plants

All green plants that have flowers are called flowering plants. Scientists have grouped these according to the number of seed leaves found in each plant.

Monocots (or monocotyledons) have one seed leaf; dicots (or dicotyledons) have two seeds leaves. These leaves provide the food the young plant needs until it can make its own food. Flowering plants consist of four main parts: (1) roots, (2) stem, (3) leaves, and 4) flowers.

Plants without flowers are called non-flowering plants, or gymnosperm. While they do produce seeds, the seed is not enclosed in a flower (and eventually a fruit) the way seeds are in flowering plants.

Non-flowering plants are very common, and include conifers (evergreens), cycads, and ginkgo. Popular types of conifers include fir and pine trees. These trees are characterized by sharp needles and produce cones that hold the seeds.

There are two different types of trees: non-flowering trees that have seeds that are not enclosed, and flowering trees that have seeds that are enclosed. An example of a non-flowering tree would be an pine tree. An example of a flowering tree would be a fruit tree, such as peach or orange.

Flowering trees are deciduous; that is, they shed their leaves every year. Other trees are conifers; they grow new leaves before shedding old ones, and stay green all year round (“evergreen”). Trees consist of roots, trunk (stem), branches, twigs, and leaves. The tallest trees in the world are the redwoods of

Some of the food we eat comes from roots, like carrots, beets, turnips, radishes, and potatoes. These are roots that store food for the growing plant. Radishes—an edible root.

Leaves help plants make their own food. Within the leaf is a green material called chlorophyll. Chlorophyll absorbs sunlight to make a natural sugar that the plants uses for food. This process is called photosynthesis. During photosynthesis, carbon dioxide is used by the plant, and oxygen is released. This makes trees and plants a great way to keep the air on earth fresh and clean.

The leaf has veins for carrying this sugar to other parts of the plant. The flat, green part of the leaf is called the blade. The edge of the leaf is called the margin. A good nickname for leaves is “suncatchers”, because they catch the sun that the plant needs

to make food. In the fall, leaves lose their chlorophyll. That allows the other colors in the leaf to show, so that we see yellow, orange, red, and even purple leaves.

Plants use flowers to reproduce (make more of themselves). The flower’s job is to produce a fruit, which contains seeds. Flowers are used by humans to add beauty to outdoor and indoor areas, and some flowers can also be eaten.

Flowers, or blossoms, are made up of petals, called the corolla, which are usually brightly colored. The bright colors attract birds and insects, who spread pollen from one flower to another. This fertilizes the seeds and allows new plants to grow. Other parts of the flower include the calyx, the green leaves that surround the petals; the stamen, which produces the pollen; and the pistil, which receives the pollen from another flower to fertilize the plant.

Many plants use seeds to reproduce. A plant produces a very small version of itself, called an embryo. This embryo, together with its stored food, is covered with a thin covering called the testa (seed coat). The embryo, stored food, and testa make up the seed. This seed will grow into a new plant. The seed uses the stored food to grow until it is big enough to make its own food, using its leaves. The seed coat protects the seed until it is ready to grow. For a seed to germinate (start to grow), it needs to be in moist soil. The water causes the testa to split apart. Then the root tip of the seeds can grow into the ground. Plants spread their seeds in many ways. Some seeds are blown by the wind; others are carried by insects, birds, or mammals. Nuts, a type of seed, are often buried in the ground by animals and some result in new plants. Some seeds fall into water and are carried to new places. Some plants grow a covering for their seeds. This ripened part of the seed is called fruit. Tomatoes, apples, and peaches are some of the plants that grow in this way. Vegetables are actually the fruit part of the plant. Generally, the ripened part of the plant is called “fruit” if it is sweet, and “vegetable” if it is savory, or less sweet. The outer skin of the fruit is called the exocarp. The fleshy part of the fruit, the part we eat, is called the mesocarp. The inner part of the fruit that covers the seeds is called the endocarp. All three of these layers put together are called the pericarp. Humans and animals use fruits and vegetables as a great source of food. Most fruits can be eaten raw, although they can also be cooked or baked. Vegetables generally taste better after being cooked.

There are several different types of stems. Flowering plants like carnations and tomatoes have soft stems. Trees and bushes have hard, woody stems. Woody stems have an outer covering called bark. Underneath the bark is a layer of growing cells called cambium. Every year, trees grow another layer of cambium. Counting these layers (or rings) tells you how old the tree is.

The stem of a plant has four main jobs: (1) to support the leaves, flowers, and fruit of the plant; (2) to act as a highway, bringing water and nutrients to the plant; (3) the storage of food for the plant; (4) producing new living tissue for the plant.

Some stems are edible—asparagus and celery are two examples.

The four types of plants and their role

Four types of edible plants are available for conducting a grazing enterprise. They are annuals, perennial grasses, perennial edible shrubs and fodder trees. Each type is very different in so many ways, with each type having a specific role. Those who have managed in both good and bad years, quickly come to realise that there was no such thing as the best plant. In good years the most productive plants are most appreciated and in the bad years the hardy ones. Each type has different management requirements and each type has a particular mechanism that ensures survival.

 The four plant types animals rely on for energy and protein annuals, perennial grasses, perennial edible shrubs and fodder trees How well these different groups are understood and how well they are managed, will make or break the grazing business and the landscape. When the four plant types are discussed, it is important to remember that there are the two seasons, summer and winter. There is also extreme variation in rainfall from year to year. Just as animals need a variety of plants in the landscape for production and survival, likewise, soils function better if there is a variety of plants to allow carbon flows to be maximised over time. Nutrient cycling is more successful with a variety of plants. Some decompose quickly to release their nutrients, while others have deeper roots and are able to source nutrients that have escaped deep into the soil and return them to the surface. If there is going to be climate change, due to global warming, then the location of specific species may move further south, as that is where their ideal environment will be.  Annuals are the opportunists of the pasture system and can be either grasses or broadleaf plants. They grow rapidly from seed when moisture and nutrients allow, and escape the adverse periods. With climate change, they might become less available due to increased variability in rainfall.

Perennial grasses are less palatable than the annuals, but supply the bulk of feed over time, if they are present. Perennial grasses are our most valuable resource, as they stabilise the landscape, trap nutrients and moisture, and provide animals with a readily available long term feed reservoir.

There are two basic groups of perennial grasses, the C3 group and the C4 group. The two groups absorb carbon dioxide differently through the process of photosynthesis. The two groups have different optional growing temperatures, with the C4 group functioning better at higher temperatures. The C3 plants need higher moisture and have higher nutrient requirements. In the areas suited to both groups, which is a large area of Australia, it is management which determines the availability of the more palatable C3 grasses.

Perennial edible shrubs include a variety of species, but the focus here will be on the main type, the saltbushes (chenopods). They are drought resistant, frost resistant and kangaroos do not eat them, so they are a long term source of "green leaf". It is their deep roots of up to 4 metres, and slower growth that makes them drought resistant. They can obtain moisture at depth during dry times, like trees do. Their leaf structure reduces transpiration, which increases water use efficiency.

Saltbushes are often criticised for being less palatable than the herbages and grasses, but this is their attribute as it guarantees they are still available for animal production and survival, when all other plants have failed. They are often incorrectly promoted as a fodder supply for dry times. Their true role under these conditions is to supply protein to allow ruminant animals to digest unproductive grasses and leaves.

For many, saltbush is just part of the nostalgia of the early settlers and the outback of Australia, as we like to romanticise it. The reality is that saltbush is a management tool supplying ecosystem services to the environment. An example of an ecosystem service supplied by Old Man Saltbush is its ability to change the soil structure in degraded landscapes, and so allow more water and air in. This results in the landscape becoming a more friendly environment for grasses to then enter. With the arrival of perennial grasses between the Old Man Saltbush, there is further ongoing introduction of carbon into the landscape.

Fodder trees include the edible component of the trees in the landscape. Examples are mulga, leucaena and tree lucerne. They are able to utilise past rainfall further into the future and they are part of the reliable component of the fodder supply.

Leucaena and mulga have the added advantage of directly introducing nitrogen into the landscape. If they are not a monoculture, then they can enhance the ability of grasses to introduce more carbon into the landscape.

In a country where we have the most unreliable rainfall in the world, the emphasis must be shifted to increasing the percentage of perennial plants in the pasture, be they grasses or shrubs. It is the perennials that can respond to isolated single falls of rain, while annuals can't.

It is the perennial grasses that are best at introducing carbon into the landscape. It is the perennials that we are thinking of with the statement "carbon makes carbon". Just as having money and managing it properly leads to more money, so having perennial grasses and managing them correctly, leads to more perennial grasses, (and hence further additions of carbon).

A correct balance of plants leads to ongoing photosynthesis (carbon storage) under all seasonal and climatic conditions, with the possible exception of extreme drought.

Maximising landscape carbon and soil carbon is all about trapping sunlight at a multiple of levels. Recycling of nutrients is all about having different depths of roots to bring the nutrients to the surface. Nutrients and carbon go hand in hand. Planting fodder trees, Old Man Saltbush, or any tree, into areas of straight grass, is returning the vegetation layers, just as thinning dense regrowth and allowing grass to grow is returning a vegetation layer.

How plants function

Root growth and leaf growth are related. Therefore animal grazing affects both the leaves and the root system. Excessive removal of leaves reduces the ability of plants to build and maintain good root systems. Plants need an extensive root system in order to extract what they need to produce an abundance of fodder for animal production.

At the end of dry times, perennial grasses are dry old butts that have no green leaves to promote photosynthesis. Yet they grow with the arrival of rain, so obviously they have a mechanism to start growth after rain. We know that plant growth requires energy, so it is obvious that they must be sourcing energy from somewhere.

To explain this last point, the roots hold reserves of plant carbohydrates (starches/energy) needed to stimulate growth when growing conditions arrive. Some reserves are also held in the crown of perennial grasses. Apart from instigating growth after dormancy, these root reserves are also important for maintaining tissue during drought, when photosynthesis is not occurring.

The most dangerous time for perennial grasses is a run of marginal years when stock eat all the new growth every time there is some rain. This results in root reserves being drawn on regularly with little replacement, and so some plants eventually die. This is what David Freudenberger of CSIRO refers to it as the paradox of average years. Green pick is ongoing so root reserves are at risk.

Plants are the ultimate net workers who supply partners everywhere in order to get what they want done. Plants need food and water the same as humans. Apart from the carbon in the atmosphere being a food source, plants get the other things they need out of the soil. For this reason they have to ensure that their helpers in the soil construct a soil that is full of nutrients, water and air. These helpers either leave the construction site or die if plants do not feed them. Stressed and dying plants lead to unhealthy soil as they do not feed the below ground food chain

The carbon: nitrogen ratio

The carbon : nitrogen ratio (C:N ratio) of living things and their residues is essential for determining the outcomes of many processes. This ratio is always discussed in papers looking at landscape function and animal performance, yet it is rarely discussed in literature available to rural producers.

The first thing to understand about plants is that the carbon is fairly constant in the break-up, it is the nitrogen that varies. Most trees are about 50% carbon while grasses are about 45% carbon. Like all figures used in plant analysis, this is based on a dry weight.

As the plants are the start of the two food chains, above and below the ground, the C:N ratio of the plants will determine how efficient these other consumption processes are.

In plants, nitrogen is necessary for chlorophyll synthesis, and as part of the chlorophyll molecule, is involved in photosynthesis. It is chlorophyll that gives the plant its green colour. Lack of nitrogen and chlorophyll means that the plant will not utilise sunlight as an energy source to carry out its essential functions such as nutrient uptake. A badly managed pasture with low soil carbon levels, and hence lower nitrogen levels, struggles with carbon introduction following rain, due to a lack of nitrogen. Dysfunctional landscapes become increasingly infertile, because they have a low potential for capturing new resources.

Discussions often focus on how different plants have different nitrogen levels. However, it is also important to appreciate that the nitrogen levels vary within a plant. This is why animals, especially sheep, will select certain plant parts over others.

In the future, more attention will be placed on the C:N ratio of the diets of ruminant animals, as it influences the production of methane per kg of production.