Of the approx. 92 chemical elements that occur naturally, only 17 are considered essential for proper plant growth and development: Carbon, hydrogen, oxygen, phosphorus, potassium, nitrogen, sulphur, calcium and magnesium are needed in relatively large amounts; molybdenum, nickel, copper, zinc, manganese, boron, iron, and chlorine in lesser amounts. Of those, plants obtain carbon and oxygen primarily from the atmosphere (the “air”) while they extract the rest from the soil (the “earth”).
Combined in different ways those elements make molecules such as proteins, fats, nucleic acids, and carbohydrates – which are used in the construction of plant cells. Many of the metals act in partnership with enzymes helping to ensure that the biochemistry necessary for proper functioning of the plant takes place. Other metals are involved in processes that produce energy via photosynthesis and by respiration.
The Sun is the ultimate “fire” in the life of plants. But that star produces much more than ‘fire’, the infra-red heating wavelengths of the electromagnetic spectrum. Accordingly, fire is interpreted as the full range of solar wavelengths – which also includes light (visible wavelengths), used importantly in photosynthesis.
Heat from the Sun is thus responsible for providing a suitable temperature range which sustains the life of plants (and other organisms). The Sun’s light is extremely important to plant life; differences in both its quality (wavelength, colour) and quantity are amongst the most influential factors on plant development as underlined by the range of plant biological processes that start with the prefix ‘photo-’ e.g., photosynthesis, phototropism (directional growth of plant parts in response to light), and photomorphogenesis (development of plant form and structure in response to light).
Although our planet’s atmosphere (the air) contains many components, oxygen and carbon dioxide are of most relevance to our elemental view of plant biology. The air therefore provides plants with two essential nutrients – carbon (as CO2), which is incorporated into organic compounds for plant growth by photosynthesis, and oxygen, which is essential for respiration.
And moving air – i.e. wind – can help to mould a plant’s shape, providing a graphic example of the way in which plants can be formed from this fundamental element.
Water accounts for up to 95% of the mass of growing plant tissues and is the major component of the vacuole, often the largest component of the plant cell. The vacuole is essential to plant growth because it causes the cell to expand as it swells to its full volume by uptake of water. It is this expansion of individual cells that ultimately leads to growth of the entire plant.
But water has many other roles that help to make the plant: as the driving force behind many growth movements; as a medium for the transport of sugars from photosynthesis to all growing regions; as a reactant (e.g. in photosynthesis); and as a promoter of germination (hydration of dry seeds is one of the first stages in the germination process).
Getting the balance right
Just as ancient medical practice believed that an imbalance of these four elements caused harm to humans, so too with plants. Generally, you need the right balance of everything for a properly functioning individual. If one, such as water, is in excess – e.g. in flooded soils – or is insufficient as in arid deserts – plant growth will suffer. And this is a problem for Mankind because such fundamental environmental stresses experienced by our crop plants are some of the most serious constraints on current agriculture and future global food security.
We rightly applaud mankind’s ability to create new chemical elements. However, we should also celebrate the amazing achievement of plants who long ago worked out how to make a complete life form from the four fundamental ‘elements’, fresh air, soil, sunshine and water.
[Images: Author’s own]
* I thank Miriam Frankel and Angela White of The Conversation who contributed edits to an earlier version of this piece.