Solar Energy FlowSolar energy flows in one way, from the sun to the earth. Unlike water and minerals it does not cycle.
Solar energy, which is necessary for almost all organisms on the planet to be sustained (although there are a few species in warm ocean environments that are adapted to nil light conditions) is captured and converted to a useable form (very often grass or grain, but also vegetables, fruit, nuts etc) through the photosynthetic process, which only occurs in green leaves, in the presence of chlorophyl.
The process can be considered as a broad based upward and downward flow, where the bases join at the soil surface.
Factors effecting the amount of solar energy captured
The strength of the energy flow onto a piece of land is dependent on:
- The volume of green leaf available to perform photosynthesis.
In its simplest form, a small amount of leaf area captures a small volume of sunlight.
- The time over which photosynthesis is able to occur—usually most influenced by the effectiveness of the water cycle on a piece of land, and by the species present in the local environment, which is a reflection of the level of biological succession, or community dynamics.
If a landscape is green and capable of capturing sunlight for only a short time each year, the amount of sunlight that may be captured is severely limited. The South-west of Western Australia is just such an example, where on a vast scale there is often no capture of solar energy for between 180 and 210 days of each year.
- The rate at which photosynthesis occurs—also a reflection of the effectiveness of the water cycle and the mineral cycle, and of the level of succession of the plant species present.
Narrow leafed plants tend to capture less sunlight than broad leafed plants. Plants such as cactus, and rushes and sedges, who each have a waxy surface are deliberately minimising the amount of sunlight energy they can absorb.
Low successional plants have a number of devices for reducing the amount of sunlight they can capture. They do this because they are adapted to conditions such as ineffective water cycles, where rapid respiration would lead to their own demise.
Many plants reduce their solar capture by reducing the area of leaf exposed to sunlight. Narrow leaves are a common choice in this regard, whilst some plants are able to alter their leaf position relative to the sun, by turning their leaf edge rather than the face of the blade towards the sun.
Many plants have waxy cuticles on their leaves. Members of the cactus species are well known in this regard, as their biological or sucessional niche is towards the low end of the scale. They are adapting to ineffective water cycles. Cactus plants are known as xerophytic or ‘dry’ type plants for this reason—they exist in dry locations
Many of the rushes and sedges have a similar device for minimising solar flow. They are also low successional plants, but are known as hydrophytic or ‘wet’ plants. Such plants tend to exist in water logged, ineffective water cycle conditions which prevent rapid respiration.
The desirable plants from a productive point of view are all known as mesophytic or ‘middle’ type plants. Such plants are characterised by the capacity to respire rapidly when adequate water and sunlight are present.
Not all the energy that is captured is available for productive use. Some energy is utilised just to sustain the basic functions of life such as respiration.
The energy pyramid below shows the heat loss, and how energy is utilised by different organisms in the pyramid, with the ultimate end being decay.
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