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of the Environment

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By this term we mean everything that surrounds the plant and affects it. This is made up of:

Non-living components – Abiotic

Living components - Biotic

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These components may be grouped in three categories:

Atmosphere – including climate and weather

Soil – including its physical and chemical composition

Water – found both in the atmosphere and soil

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Because of its presence in both atmosphere and soil, water will be included in both the other two categories.

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The main environmental factors of the atmosphere are:

Light – quality, intensity, duration

Temperature – cold and heat

Meteoric Phenomena –wind, rain, hail, etc.

Composition of the air –pure elements and compounds.

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Sunlight is the primary source of energy in nearly all ecosystems.

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Visible light is of the greatest importance to plants because it is necessary for photosynthesis.

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Light is the energy that is used by green plants (which contain chlorophyll) during the process of photosynthesis; a process

during which plants manufacture sugar by combining water (found in the soil) and carbon dioxide obtained from the air.

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Photosynthesis is the ‘knitting’ together of carbon dioxide from the air and water from the soil to produce simple sugars. The energy needed to do this comes from light.

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Light requirements of plants differ and, as a result, distinct layers, or stratification, can be observed in an ecosystem.

Plants which grow well in bright sunlight are called heliophytes(Greek helios, sun) while plants which grow well in shady conditions are known as sciophytes (Greek skia, shade ) 12

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Factors such as the following all play an important part in an ecosystem.

• quality of light,

• intensity of light

• length of light period (day length)

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Quality of light refers both to its wavelength and its colour.Plants absorb blue and red light during photosynthesis.

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The intensity (i.e “strength”) of the light reaching earth varies according to the latitude and season of the year.

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The northern hemisphere receives more than 12 hours of sunlight between 21 March and 23 September, less than 12 hours during the following six months.

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The northern hemisphere receives more than 12 hours of sunlight between 21 March and 23 September, less than 12 hours during the following six months.

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Certain plants flower only during certain times of the year. One of the reasons for this is that these plants are able to "measure" the length of the night (dark periods).

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However, it was at first thought that it is the day length (light periods) to which plants reacted and this phenomenon was termed photoperiodism.

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Photoperiodism is the relative length of daylight and darkness that effects the physiology and behaviour of an organism.

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These plants flower only if they experience nights which are longer than a certain critical length. Chrysanthemum and poinsettia are examples of short day plants.

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These plants flower if they experience nights which are shorter than a certain critical length. Spinach, wheat and radish are examples of long-day plants.

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The flowering of day-neutral plants is not influenced by night length.

Tomato and maize are examples of day-neutral plants.

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Phototropism is the directional growth of plants in response to light.

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Photonasty is the movement of parts of a plant in response to a light source, but the direction of the stimulus does not determine the direction of the movement of the plant.

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We can see the dramatic effects of lack of light on a cactus.

The cladodes which have developed in lack of light are small, elongated and pale.

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On this plant we can see where it was growing in dark conditions (the etiolated part).

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Sometimes, lack of light is used by farmers to produce “white” vegetables such as leeks and celery. This is done by covering part of the plant so that it grows in darkness and does not develop chlorophyll.

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Too much light can also be harmful for some plants especially ornamental ones.

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Although most crop plants need plenty of sunlight, this can also become harmful of there is too much of it. In warm places like Malta “overdose” of light is exacerbated because it is always accompanied by high temperatures.

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These are examples of sunburn on fruits.

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The distribution of plants and animals is greatly influenced by extremes in temperature for instance the warm season.

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The occurrence or non-occurrence of frost is a particularly important determinant of plant distribution since many plants cannot prevent their tissues from freezing or survive the freezing and thawing processes.

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The opening of flowers during day or night is often due to temperature differences between them.

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The seeds of some plants normally germinate in spring or summer after having been through a period of low temperatures; a phenomenon known as vernalisation.

This chilling ensures that the seeds don't germinate during autumn so that the seedlings have better chances of survival in the warm weather.

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This can also be observed in bulbs which normally flower in early spring but can be forced to bloom out of season by being subjected to a period of chilling. 44

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Some fruit trees such as the peach require a cold period each year so that they can blossom in spring.

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Deciduous trees lose their leaves in winter and enter into a state of dormancy, where the buds are covered for protection against the cold.

Peach buds Plum buds 46

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Cherry buds Apricot buds

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In deserts, there is a greater temperature variation between day and night and organisms have distinct periods of activity and dormancy.

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High temperatures cause damage not only directly but also because

they are usually accompanied by low humidity and draught. This

causes dehydration of the plant tissues and result in its death.

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Low temperatures can hinder and inhibit the rate of development and cause bloom fall. Most plants are damaged if temperatures drop below 0° C.

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Effects of extreme cold on oranges

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Right: Leaf death due to excessive hot temperatures and dry winds.

Below: Kernel abortion resulting from heat stress to plant.

Bottom rigght: Kernel abortion resulting from heat stress to plant.

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Capsicum under extreme heat.

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By this term we refer to the chemical elements found in the air.

Apart from the natural elements one can also find more complex compounds, some of which are harmful.

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The most important gases used by plants and animals are:

Oxygen (O)is used by all living organisms during respiration.

Carbon dioxide (CO2) is used by green plants during photosynthesis. Nitrogen (N) is made available to plants by certain bacteria and through the action of lightning.

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Winds or air currents arise on a world-wide scale as a result of a complex interaction between hot air expanding and rising (convection) in the mid-latitudes.

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This has various effects on the rotation of the earth and results in a centrifugal force which tends to lift the air at the equator. This force is known as the Coriolis force and tends to deflect winds to their left of the southern hemisphere and to the right in the northern hemisphere.

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Winds carry water vapour which may condense and fall in the form of rain, snow or hail.

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Wind plays a role in pollination and seed dispersal of some plants.

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Wind erosion can remove and redistribute topsoil, especially where vegetation has been reduced and the soil loosened by cultivation

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Diagram showing the effects of wind on soild particles of different sizes.

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Warm dry winds result in desiccation which creates a fire hazard.

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If plants are exposed to strong prevailing winds they often grow in particular shapes to withstand the constant strain.

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In the context of this presentation, “meteoric” is used in the sense of meteorological, that is, weather events. These obviously have a direct effect on plants and animals living in the areas where the occur. 73

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Plant and animal habitats vary from entirely aquatic environments to very dry deserts. Water is essential for life and all organisms depend on it to survive in especially desert areas. 82

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Plants can be classified into 3 groups according to their water requirements:

Hydrophytes

Mesophytes

Xerophytes

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Hydrophytes are plants which grow in water e.g. water-lilies.Mesophytes have average water requirements e.g. most crops.

Xerophytes grow in dry environments e.g cactus.84

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Water cycles through the biosphere in the manner is described in the figure below and on the next slide.

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When rain falls, some of the water sinks or percolates into the ground and saturates the earth to a certain level. The top of the saturation level is called the groundwater table or simply the water table.

Ground water is also sometimes located in a porous layer, called an aquifer, that lies between two sloping layers of impervious rock. Wells can be used to extract some of this water for human consumption.

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The effects of too much or too little water on the plant will be discussed in the soil section of this course.

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As each plant has a specific water requirement and both extremes, too much or too little, are harmful. Even a fluctuating supply can up the plant’s metabolism and be detrimental.

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Waterlogging causes yellowing of leaves, stunted growth, small and shallow root systems in plants.

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Soil flooding for a sufficiently long period of time will cause plant roots to die of asphyxiation.

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Waterlogging prevents the roots from functioning properly and this causes, among other things, wilting and leaf-drop.

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Too much water causes roots to rot, unless the plant is specially adapted to such a condition.

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Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening. As the exposed surface cools at night the moisture in the air condenses and forms water droplets.

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In dry Mediterranean climates, dew is an extremely important source of water for trees in summer. 100

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On the island of Pantelleria, special structures are built around single citrus tree. These are know as “giardini Panteschi” and are essential for the survival of the tree.

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Dew is collected on the stones forming the walls and this provides enough moisture for the orange tree to survive. 103

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Dew is essential for the survival of many plants in hot dry summers but it can also favour the onset of disease as many fungal pathogens thrive in the high relative humidity.

104Mould forming on grapes.

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Many fungal pathogens are so dependent on the right environmental conditions (T and RH) that farmers can predict when attacks will take place by looking at weather forecasts.

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The formation of mist follows the same principle as that of dew. Water moisture in the air condenses and forms tiny droplets.

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Hail damage on tomato plants.

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Deciduous trees drop their leaves to protect themselves from the effects of snow and very low temperatures.

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Conifers have physical adaptations - especially in their leaves - to withstand being covered in snow without suffering injury.

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When immature crops are damaged by frost, yield and quality can all be affected.

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The effect of frost on yield depends on how much leaf area is killed and the stage of development when the frost occurs.

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When only a portion of leaves are killed, those not killed can and will continue to function and contribute to yield if good growing conditions exist after the frost.

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