When describing plant food (fertilizers), N-P-K (Nitrogen- Phosphorus - Potassium) are the basic metrics. There are others too, but these are the most important ones.
When describing animal food (and I know only about human foods), the basic metrics like Protein, Carbs, Fats , etc. have the potassium and phosphorus missing. (Nitrogen is there as protein).
Although we are in the same food chain, it seems like Potassium and Phosphorus a basic nutrient for plants but not so important in animals (humans).
To clarify, I am fully aware of the role Potassium and Phosphorus play in the animal system.
The question is: why are plants more prone to Potassium/phosphorus deficiency than animals/humans ? (Or are they ?)
Potassium and phosphorus both have essential roles in plants and animals. The difference is primarily that plants must get these items from the soil, while animals pick them up from the foods they eat. Many foods have adequate phosphorus and potassium, while soils are prone to exhaustion of phosphorus and potassium.
If plants have been growing in the same soil for a while, they may use up the available potassium and phosphorus, so it has to be replaced. Animals of course have opportunities to pick up more P and K every day; plants do not unless you feed them.
Note, however, that potassium and sodium are lower in plant tissues than they are in animal tissue. For this reason herbivores may be prone to deficiencies in this elements and so may need to visit salt licks to acquire them.
Over-simplyfing greatly, and with apologies to Colibri: who’s already given a good treatment:
Plants are autotrophs. They use inorganic, mineral sources, and solar energy to make complex organic molecules to support their life processes. If their local source is depleted, they die, perhaps without reproducing.
Animals are heterotrophs, they absorb complex organic molecules and change them into different complex organic molecules to support life processes. If animals detect a local shortage of high energy pre-made complex molecules, they do something about it, moving, until the problem gets solved. Or they fail and die, possibly without reproducing.
You can’t consider the NPK fertilizer nutrients in a mental vacuum without considering how plants use sun energy to support their life processes.
Also, for plants, potassium is the primary osmoregulator – that is, the ion that makes their tissue fluids the right level of “saltiness” (for lack of a better word) to support life, mostly by folding proteins properly.
For animals, sodium is the primary osmoregulator. Different ion, same use. Not interchageable.
Plants need more magnesium than they do iron, and humans need way more iron than they do magnesium. Notice: I picked elements that fit into a heme, that fits into a large protein, that’s very important for life processes. Although they don’t work analogously in each case.
Thank you for the great responses: I understand the different role of potassium now.
Presumably vegetation has been around a lot longer than animals and they would have exhausted the soil. Why did plants evolve then to be dependent on potassium and phosphorus?
As I understand, animals tried different metals for transporting oxygen in their blood (copper, vanadium, etc.) and settled with iron because of its abundance.
Why did plants keep their dependence on potassium / phosphorus? I ask this specifically because as a Chemical Engineer, I find these minerals to be very limited. While potassium occurs in a few countries like Canada, only one country (Morocco) holds all the world’s Phosphorus.
Actually, these minerals are essential for all life, even bacteria. Phosphorus is needed for ATP (adenosine triphosphate), the basic compound used in energy transfer processes, and is also a crucial part of DNA and RNA, binding the nucleotides together. No organism can do without these. You don’t get to “choose” whether to need these minerals.
Actually, many more animal species, particularly insects and mollusks, use copper compounds (hemocyanin) for oxygen transport than use iron compounds, which include mainly vertebrates. I don’t think abundance has anything much to do with the fact that vertebrates use iron. Vanadium is a very unusual case found in tunicates and ascidians, and it appears they actually use hemocyanin for oxygen transport rather than vanadium.
Phosphorus is the 11th most abundant element in the Earth’s crust. What you are talking about is the mining of phosphate, not phosphorus itself. China is by far the greatest producer of phosphate, with the US being second and Morocco a close third. The potassium in rocks is largely locked up in forms that are not available to plants, and it has to be converted to other forms such as phosphate before they can use it. Historically much phosphate used for fertilizer came from biological sources such as guano. However, even other phosphate deposits may be also derived partly through biological processes.
There are dozens of threads asking why this evolved or that evolved. People will be by shortly to let you know that evolution is a process that just happens – your definition of “fitness” doesn’t apply.
As was said, phosphorus is abundant enough to vegetate the Earth and its oceans for millions of years. Humans have been farming for 40,000 years. Remove all notion from your mind, that plant evolution remotely needed to adapt to the contemporary agribusiness.
Phosphorus is the backbone atom of the DNA molecule. No living thing on Earth is going to “evolve” out of its dependence on DNA – what would it use to evolve new traits with?
