Newly mobile manganese may be taken-up into the tree, poisoning the shoot. As saturated soil conditions continue with no oxygen present, and nitrogen and manganese are used-up as electron acceptors, iron becomes a respiration element. Iron respiration allows insoluble forms of iron to be changed into soluble forms. Like manganese, soluble iron can produce many toxicity problems. After a time, cells have trouble transferring electrons to the environment because the concentration of electrons inside the tree andoutside the tree are about the same.
Sulphur becomes the next element used by soil organisms as an electron accepter.
Sulphur respiration can cause hydrogen-sulfide to be produced, which is highly toxic to tree roots. Sulphur respiration also causes many compounds to bond with sulfides making them insoluble and unusable. At the end of the respiration process with no oxygen, comes fermentation. Fermentation is the transfer of electrons to carbon. Compared with normal respiration, fermentation respiration consumes twenty times the amount of food for the same amount of energy produced.