Nitrogen fixers that tolerate partial shade
Tall trees
Smaller trees/large shrubs
Smaller shrubs
Perennials
Potassium
Potassium is more difficult to supply on site than nitrogen. Potassium is particularly important for making the cell walls thick, which in turn is important for resistance to diseases, pests and animals. Almost all soils have plenty of potassium, but most of it is unabsorbable and is made available by weathering. Wormwood and certain ferns have a high content, which it releases every fall. A woodland garden attracts plenty of birds, which in turn add a lot of potassium via their droppings. Wood ash is also a good alternative if you want to add something from the outside. Plants rich in potassium that they release in the fall:
Phosphorus
The soil generally contains more than enough phosphorus and you rarely need to do anything extraordinary. Artificial fertilizers have unnecessarily large amounts in them. Again, wood ash is a good alternative if there is a phosphorus deficiency in the soil.
However, the phosphorus deficiency in the world's phosphorus mines is a growing problem for the world's food supply. Fungi absorb many minerals, including phosphorus, which they release in an easily absorbable form through exchange or by dying and rotting. Psilocybin mushrooms in particular absorb large amounts of phosphorus to synthesize the psilocybin molecule which can contain as much as 2% of the mushroom's mass. Psilocybin mushrooms are easy to grow, and can be co-planted with annual crops. Cultivation guides for mushrooms are being prepared here.
Other sources of fertilizer
Wormwood is the easiest plant to grow that adds plenty of extra nutrients to the soil. The reason for this is that it develops very deep roots that draw up minerals from deeper layers of the soil.