There’s bacteria that grow in the roots of legumes that are capable of capturing gaseous nitrogen. That nitrogen makes its way to the soil, where the trees can suck it up to produce protein, like sunflower seeds. I eat those and by the time I urinate and die the nitrogen has been so concentrated within me that I burn a small hole in the ground for the fungus, sun, and time to decay and heal.
If I could photosynthesize the carbs needed to bootstrap this operation I would. If I could plant a piece of myself and feed it rainwater and atmospheric nitrogen to grow a steak I would. If I could leave behind shelter I wood.