Nitrogen makes up most of our atmosphere, it gets fixed by bacteria, legumes, etc., and enters the soil in a different form to be used by plant life. The nitrogen gets buried in sedimentary rock over time until it is released into the atmosphere by tectonic activity. Nitrogen in the soil is a limiter, in most places there's more growth and plant activity than there is in the soil. Increasing the supply in the soil could change soil composition in a good way or eventually at a high enough rate I am sure in a bad way. On earth nitrogen can negatively effect certain ecosystems so I would expect plant life on a world to evolve differently. I also know that nitrogen narcosis puts the limit on pressure at 2-4 Atmospheres for humans. So I ask how much more nitrogen in an atmosphere and soil could an alien world have, and what kind of changes to plant life or the equivalent would people see. I don't think I want more than 2 bar or atm.
Edit: logging in through gmail is a hassle, anyways, the Question is somewhat correct, and somewhat wrong. There is a large amount of activity within the nitrogen cycle, but after looking at the surface has to offer, it appears that we should focus first on nitrates and nitrites in the soil. These have limits for plant life, eventually too much in the soil will prevent plants from finding anything else it needs, and it can lead to "root burn" or damage to it's leaves. There is also the question of storage and how much can the soil store before runoff becomes an issue. The answer and another place to store the nitrogen is within the plants themselves, it is possible as mentioned by myself that instead of increasing atmospheric nitrogen it could be drained for resources. So a better two questions would be in what ways can Plant or Fungal life use more nitrogen and how can we change nitrification or denitrification in a system Some answers would be to change photosynthesis and the use of sugars, cellulose, or really anything that a plant uses Carbon for.
So some possibilities would be in replacement of glucose with something that uses more nitrogen as energy storage seems to be a significant source of a demand for carbon in a plant, this is a good place as leaves use CO2, and the source of demand will be where it could take in N2.