Late to the party, but I want to answer your question more directly than others have, because while they might be correct in part, they are missing, perhaps some of the most important and direct aspects of an answer, which is, yes there is a reason for this, and the answer is evolution, but almost assuredly not in the way you might be thinking.
Specifically, its that the composition of the atmosphere itself is a result of evolution. And the nature of how nitrogen fixation needed to evolve, the specific conditions required, and the shift to oxygen as the terminal electron receptor resulted in the singularly most massive shifts in all of biological history of all time. So yes, “evolution”, but actually, the order of operations goes in the other direction, and the very nature of nitrogen fixation is an evolutionary artifact of this.
Life on early earth was almost entirely anaerobic. They did not use oxygen as the “terminal electron receptor”, which in a molecular sense is far more “down hill” from other molecules, and thus, you can get far more energy if you can land your electrons on oxygen at the finish line. However, oxygen is a greedy fucking bastard who will basically tear apart anyone or anything to get back to that ground state; hence the need for so many antioxidants in plants, animals, fungi: because our shit gets fucked up by oxygen. Early earth simply didn’t have oxygen in any significant amounts. Why? See the previous point. Oxygen is a greedy fucking bastard that doesn’t want to stick around. Its desperate to get back to a more neutral ground state.
In the absence of oxygen, there are other options one can use as a terminal electron receptor, and specifically, N2 can be used to be that ground ground state. However, the enzyme which catalyzes those reactions, nitrogenase, gets its shit COMPLETELY fucked by oxygen. But for literally billions of years, life worked without oxygen, and nitrogenase was central to this process.
Enter the period of about 2.5 billion years ago, and introduce the “Great Oxygen Holocaust”. Basically, what happened, is some cunt of a cyanobacteria figured out a way to perform oxygen photosynthesis, effectively splitting water, which both uses and creates oxygen (which is a bi-product of the reaction) to create significantly more energy. Its no coincidence that the spectral absorbance lines of chlorophyll and the spectral emission lines of hydrogen line up like they do. But what about nitrogen? All my homies LOVE nitrogen still. What happened?
What happened was the total and complete destruction of the worlds ecosystems as they would have been. This was the great oxygen holocaust and it literally changed earth systems beyond recognition. Evolution had gone so far as to literally make the types of chemistry and geology that were happening before the evolution of oxygen photosynthesis impossible.
And with that, nitrogen fixation is totally fucked in the context of an oxygen atmosphere. Like it just literally can’t happen, but just because some organisms found a better way to do photosynthesis, doesn’t mean that they stopped needing nitrogen. They still need it, but they were now pretty fucked in their ability to create it. And we see that in the types and approaches for nitrogen fixation that are still present today. If you want to do if you want to do nitrogen fixation today, is you have to create special cells, with extremely thick walls to concentrate and exclusively fix nitrogen, like Nostoc. Or you have to separate the process temporally (Anabaena), or if you are real tricky you hire a contractor like how legumes form nodules of Rhizobia in their roots, which are far away from where the oxygen gets generated (leaves), or tripartite cyanolichens where they create special structures for oxygen exclusion.
So yes, short answer, evolution. But its actually the other way around: Plants didn’t evolve to our atmosphere; plant evolution constructed and maintains the atmosphere we live in.
Late to the party, but I want to answer your question more directly than others have, because while they might be correct in part, they are missing, perhaps some of the most important and direct aspects of an answer, which is, yes there is a reason for this, and the answer is evolution, but almost assuredly not in the way you might be thinking.
Specifically, its that the composition of the atmosphere itself is a result of evolution. And the nature of how nitrogen fixation needed to evolve, the specific conditions required, and the shift to oxygen as the terminal electron receptor resulted in the singularly most massive shifts in all of biological history of all time. So yes, “evolution”, but actually, the order of operations goes in the other direction, and the very nature of nitrogen fixation is an evolutionary artifact of this.
Life on early earth was almost entirely anaerobic. They did not use oxygen as the “terminal electron receptor”, which in a molecular sense is far more “down hill” from other molecules, and thus, you can get far more energy if you can land your electrons on oxygen at the finish line. However, oxygen is a greedy fucking bastard who will basically tear apart anyone or anything to get back to that ground state; hence the need for so many antioxidants in plants, animals, fungi: because our shit gets fucked up by oxygen. Early earth simply didn’t have oxygen in any significant amounts. Why? See the previous point. Oxygen is a greedy fucking bastard that doesn’t want to stick around. Its desperate to get back to a more neutral ground state.
In the absence of oxygen, there are other options one can use as a terminal electron receptor, and specifically, N2 can be used to be that ground ground state. However, the enzyme which catalyzes those reactions, nitrogenase, gets its shit COMPLETELY fucked by oxygen. But for literally billions of years, life worked without oxygen, and nitrogenase was central to this process.
Enter the period of about 2.5 billion years ago, and introduce the “Great Oxygen Holocaust”. Basically, what happened, is some cunt of a cyanobacteria figured out a way to perform oxygen photosynthesis, effectively splitting water, which both uses and creates oxygen (which is a bi-product of the reaction) to create significantly more energy. Its no coincidence that the spectral absorbance lines of chlorophyll and the spectral emission lines of hydrogen line up like they do. But what about nitrogen? All my homies LOVE nitrogen still. What happened?
What happened was the total and complete destruction of the worlds ecosystems as they would have been. This was the great oxygen holocaust and it literally changed earth systems beyond recognition. Evolution had gone so far as to literally make the types of chemistry and geology that were happening before the evolution of oxygen photosynthesis impossible.
And with that, nitrogen fixation is totally fucked in the context of an oxygen atmosphere. Like it just literally can’t happen, but just because some organisms found a better way to do photosynthesis, doesn’t mean that they stopped needing nitrogen. They still need it, but they were now pretty fucked in their ability to create it. And we see that in the types and approaches for nitrogen fixation that are still present today. If you want to do if you want to do nitrogen fixation today, is you have to create special cells, with extremely thick walls to concentrate and exclusively fix nitrogen, like Nostoc. Or you have to separate the process temporally (Anabaena), or if you are real tricky you hire a contractor like how legumes form nodules of Rhizobia in their roots, which are far away from where the oxygen gets generated (leaves), or tripartite cyanolichens where they create special structures for oxygen exclusion.
So yes, short answer, evolution. But its actually the other way around: Plants didn’t evolve to our atmosphere; plant evolution constructed and maintains the atmosphere we live in.