Combustion and decombustion would be extremely slow
without nitrogen our bodys would over oxygenate (get to much oxygen). nitrogen is important for plants, after all they breath in nitrogen and breath out oxygen.
if bacteria could not fix nitrogen in the soil ,the plants would have died and even all of us would not survive as there would be no food for us to eat. ---Lighting would be the main source of Nitrogen Fixation (plato)
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It is not so much the class of plants that do this directly but rather a class of plants that support nitrogen binding bacteria in their root nodules - these plants are the 'legumes' such as peas, beans and clover.
Most plants absorb nitrogen from Nirates in the soil. A notable exception are insectivorous plants such as the Venus Fly Trap, which lives in soils which do not have much Nitrogen - so have adapted to obtain it from another source.
possibly to much nitrogen based fertiliser
If there was only oxygen and no nitrogen present, the burning process would be more efficient and the flames would burn brighter and hotter. Nitrogen in the air can act as a diluent, which can dampen the combustion process.
Plants need nutrients but nitrogen can kill it. People say that if you put fresh manure fertilizer it can "burn" the plant its true. Sometimes it does nbut it depends on the size of the plant.
Nitrogen actually is a big part of chlorophyll which is the chemical that gives plants their dark green color. During fall plants turn colors other than green because they lose their chlorophyll. So Nitrogen does give plants the dark green color that looks so great. However, if you get too much nitrogen in the soil, then it will start hurting the plant.
Carnivorous plants don't actually EAT stuff. Plants need nitrogen as much as we need minerals so that to keep healthy, but some plants live in places where there isn't much nitrogen, and so they have to trap insects to get nitrogen from them. It may actually be FATAL to it. So you better not take the risk. Whether it is insect or food like Cheerios, Flytraps will trap it.
If the earth got pulled in closer to the sun, or if the sun expands significantly, then the earth will get much warmer. That said, nothing like that is going to happen for a couple billion years yet.