Plant Tropism

Plant Tropism advert image shown if present

Image shown for entry if relevant and present

The direction a plant moves in response to an external stimulus. If the plant growth moves towards the stimulus this is called positive tropism, whilst if growth moves away from the stimulus it is called negative tropism. The ability of plants to grow towards or away from certain conditions, helps them to optimise resources for growth and development within the prevailing environment.

There are numerous types of tropism, including:
1. Phototropism: growth moving in response to light, typically towards the light. Plants will bend towards light typically due to a build-up of auxins on the side away from the light source. This causes cells to elongate which then bend and lean towards the light.
2. Gravitropism (also called Geotropism): growth moving in response to gravity, typically with roots growing downwards into a soil (positive tropism) and shoots growing upwards away from gravity (negative tropism).
3. Hydrotropism: growth in response to water, moving towards moist conditions. Encouraging deeper and less frequent watering of a turfgrass surface will encourage deeper rooting to occur.
4. Thigmotropism: growth in response to touch or being touched. Tendrils attaching themselves around obstacles; or leaves folding (closing inwards) in response to touch, e.g. Mimosa.
5. Heliotropism: Growth moving towards the direction of the sun. Especially flowers moving and following the direction of the sun. It is the daily movement of plant features that occurs due to the sun rising in the east and sinking in the west.
6. Chemotropism: in response to chemicals. Plants will attempt to grow away from toxic chemicals and or move towards desirable nutrients within a rootzone. For this latter situation this is a key reason why it is important to ensure fertilisers are well washed into a well aerated rootzone.
7. Thermotropism: Growth in response to a heat source. Plants will start to bend away from temperatures (negative tropism) that exceed the optimum for leaf or root growth; growing towards desirable heat (positive tropism) until this is reached.