3.5.1

Factors Affecting Plant Growth

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Factors Affecting Plant Growth

A variety of different factors can impact plant growth and distribution:

Human effects

Human effects

  • Human activity can impact plant distribution.
  • For example, the trampling of small plants and young tree shoots can limit plant growth.
    • This is particularly true in woodlands with multiple walking paths.
  • Other human effects may be pollution, felling, and introduction of new plant species.
Soil pH and aeration

Soil pH and aeration

  • Most plants grown in a pH range of 5-7. Some require acidic or alkaline soils.
    • For example, rhododendrons only grow in acidic soil.
  • Factors that affect soil pH include acid raid, uses of fertilizers, and weathering of rocks.
  • Some plants need adaptions to grow in soils with low aeration.
  • For example, rice plant roots grow completely submerged in water.
    • Rice plants contain a spongy tissue called aerenchyma that allows low-resistance gas exchange between the above water and submerged parts of the plant.
Light intensity

Light intensity

  • Plants need light for photosynthesis.
  • Increasing light intensity increases the rate of photosynthesis because more energy is provided.
  • Tall plants create a lot of shade. As a result, some plants have developed shade tolerance.
    • This means they are adapted to grow at lower levels of light intensity and can grow in the shade of larger plants.
  • Plants the grow in direct light also need adaptions to high light intensity to prevent drying out.
    • These adaptions include UV-absorbing pigments and waxy cuticles.
Temperature

Temperature

  • Temperature plays an important role in the rate of photosynthesis.
  • Rate of photosynthesis increases up to the optimum temperature (about 45°C). Above this temperature, the rate starts to fall.
    • At too high temperatures, enzymes in the plant denature. This means photosynthesis can no longer occur and the plant dies.
  • If temperatures are too low, plants will not be able to grow as the rate of photosynthesis will be to low.
Presence of water

Presence of water

  • Plants need water for photosynthesis.
  • Most plants tend to require moist soils and regular rainfall to grow successfully.
  • Plants that grow climates with little water availability are called xerophytes. They need adaptions such as waxy cuticles and leaves with a small surface area.
    • These adaptions help prevent excess water loss.
  • Cacti are examples of xerophytes.
Mineral ions

Mineral ions

  • Plants need different minerals for growth.
    • For example, plants need nitrates to build proteins, magnesium ions to make chlorophyll, and phosphorus to make DNA.
  • Soils with low mineral ion concentrations can be enhanced with fertilizers.
  • Some plants are also adapted to grow in soils with low mineral ion concentrations.
    • For example, leguminous plants contain root nodules that convert nitrogen gas in air into nitrates the plant can use for growth.
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