Four main factors influence the rate of photosynthesis - soil water, atmospheric carbon dioxide, light levels, and the air temperature. Other factors, such as soil acidity, can affect photosynthesis by making the plant unhealthy. Atmospheric oxygen and nitrogen would have no effect, and plants cannot directly use carbohydrate in soil. Nitrites are not usually absorbed by plant roots - which prefer nitrates or ammonium as their sources of nitrogen for making proteins.
