You might have heard it. Ants and Acacia trees have a mutually beneficial agreement. Acacia tree provides its sugar rich sap and shelter to ants. Ants, in turn, protect acacia tree from grasshoppers and weeds.
In fact, every plant and tree on the planet forms symbiotic relationship with soil microbes for its survival.
Plants grow by trading things they produce from photosynthesis (plant sugars) for things excreted by the soil microbes (such as nitrogen, phosphorus, etc.).
In the process of photosynthesis, light energy from the sun is converted to chemical energy held within the bonds of the molecules of sugars produced. Most of the nutrients for plant growth come from the soil microbes which trade these nutrients for the carbon-based sugars produced by the plant’s photosynthesis. The plant exudes these sugars from its roots and attracts the soil biota. This all takes place in a 2 millimeter area around the roots (called the rhizosphere).
This is perfect. Plants need the nutrients like nitrogen and the soil biota need the carbon-based sugars and the chemical energy.
It is a trading economy that has been in place since the beginning of life on Earth.
Soil microbes include various kinds of bacteria, fungi and protozoa. The big microbes (like protozoa) eat the little ones (bacteria). This makes the nutrients in the bacteria’s body (most importantly, Nitrogen) available to plants through the feces of the bigger microbes.
All Carbon-based life forms generally have a ratio of Carbon to Nitrogen of around 25 to 1, but bacteria are very Nitrogen-rich and have a Carbon to Nitrogen ratio of around 5 to 1. So, a big microbe (maybe a protozoa) needs to eat 5 bacteria to get 25 atoms of Carbon, but if it does it will get 5 atoms of Nitrogen. This is 4 more than it needs, so the extra Nitrogen is excreted and becomes available to plant roots. Luckily, the plants have been clever enough to attract the microbes to the rhizospere by offering all those sugars, so it is easy to get the Nitrogen.
