The role of oxalic acid and bicarbonate in calcium cycling by fungi and bacteria: some possible implications for soil animals

Fungi can accumulate Ca in excess of t.heir apparent physiological needs by release of oxalic acid to form thesparingly soluble Ca oxalate. Fungal release of oxalic acid may also form stable complexes with other metalliccations, which would influence both soil weathering processes and release of P from Fe and Al hydroxy-phosphates. Both saprophytic and mycorrhizal fungi may be utilizing similar functional nutrient cyclingmechanisms with respect to Ca accumulation. Bacteria and Streptemyces sp. can decompose Ca oxalate, whichrecycles the cation and permits for ration of calcium bicarbonates or carbonates. Oxalate decomposing bacteriaand actinornycetes were isolated from the digestive systems of oribatid mites, earthworms, a springtail and twoimmature aquatic detritivores, a may fly and a stonefly. Earthworms and oribatid mites are among soil animalsknown to utilize or cycle substantial amounts of Ca. A proposed Ca cycle, operative by fungi, bacteria, and soilanimals in the context of the soil ecosystem, is presented.