A basic understanding of
some major plant processes will help you understand the causes behind
specific growth problems, and what precautions can be taken to solve them.
Photosynthesis is the
process by which sugars are manufactured in a plant:
Importantly, if carbon
dioxide, water or light energy are in limited supply, then photosynthesis
will be restricted. The end result is a reduction in growth due to
insufficient sugars being available for respiration.
Hence the following factors
will have a negative impact on photosynthesis:
1. Restricted carbon
dioxide supply due to poor ventilation.
2. Restricted light supply
due to inadequate lighting or
3. Insufficient water
supply due to poor system design or
Respiration is the process
of converting sugars that are produced during photosynthesis, into
adenosine triphosphate (ATP). ATP is the energy source that is used by
plants for the following processes:
1. Growth in buds, shoots,
root hairs and root tips.
2. Nutrient uptake.
3. Movement of sugars into
the phloem for distribution to other areas of the plant.
Respiration occurs in
'mitochondria', a component of all plant cells. These are very
concentrated in the areas of the most active growth.
Respiration occurs as
The above equation shows
that respiration rates decrease if oxygen availability is limited. Oxygen
availability can be hindered by several factors:
1. Insufficient new root
growth. See section on ‘roots’.
2. Insufficient oxygen in
the nutrient solution due to inadequate
This occurs when plants are subjected to excessive heat and light -
specifically when the temperature exceeds ~35OC (95OF).
In this process plants burn sugars without converting them into ATP.
Depending upon how much sugar is wasted, this causes plant growth to slow
or even cease.
Transpiration is the
process of water evaporating from a plant. This loss of water effectively
draws water, nutrients and oxygen from the growing medium and distributes
them throughout the plant. These ingredients are essential for
photosynthesis and respiration.
Transpiration mostly occurs
through the leaves. As the leaf warms during the day, water is converted
into vapour which then diffuses into the atmosphere via the leaf’s
stomata. Most of the energy absorbed from sunlight is used to warm up the
leaf for transpiration – less than 5% is used for photosynthesis.
Most of the water absorbed
by plants is transpired. The remainder is used as a reagent in
photosynthesis, in keeping cells turgid (or hydrated), and in enabling
various chemical reactions to occur.
will cause poor distribution of nutrients. In cucumbers and tomatoes this
results in symptoms such as 'blossom-end rot' which is due to a calcium
deficiency at the plant's extremities. Factors restricting transpiration
Causes of excessive rates
of transpiration are very bright light, high temperatures and strong