Ian Holdich
Member
Diana Walstad in her book Ecology of the Planted Aquarium actually talks about the beneficial aspects of having anaerobic conditions under the substrate near the plant roots. She has around several inches of soil as the substrates in her tanks. The anaerobic bacteria will use most anything for an energy source, reducing nitrates is just one of them. The bacteria can also reduce iron, sulfur, manganese, and so on. The great thing for plants is that these reduced forms are much more easily taken up, so anaerobic conditions help the plants get their micronutrients.