I am writing a sci-fi setting with space travel. In this there is an alien world important enough to require that I put thought into the ecosystem.
Unfortunately, due to plot reasons, the usual methods for advancing the nitrogen cycle aren't good enough, and to get more nitrogen oxides into the air, I need lightning.
A previous idea was to make lightning more frequent by lowering the voltage required to generate it, this does not work because low voltage lightning doesn't break apart nitrogen.
First, a summation of the planet. It is a planet warmer and a little smaller than earth but still in the habitable zone with a shallow ocean running around the equator and some ice at the poles. There are continents covered in various forms of flora and fauna. One of the continents is particularly mountainous, another one is more prehistoric with a dash of alien. Think how the world would look if all the plants had shiny stalks and dark leaves and there was no grass anywhere. The final continent has fungal lifeforms as the dominant form of stationary life.
How do I seriously up the amount of lightning planet-wide in a realistic way? I would like as plausible an answer as possible. Maths is useful but not required.