ABSTRACT
Soil-surface CO2 efflux is commonly divided into autotrophic and heterotrophic respiration. In reality it is, however, quite complex and technically difficult quantitatively to make the separation between autotrophic and heterotrophic soil respiration. Plant root respiration should be the sole and dominant autotrophic respiration component. Mycorrhizal fungi are, like other fungi, classified as heterotrophs, but serve as an integral and functional extension of the root system of the autotrophic plant. This chapter suggests they be classified as autotrophs, in line with their function, rather than based on their taxonomic position. To elaborate further, there are achlorophyllous plants, which are functional heterotrophs. Among these are mycoheterotrophs, which receive their carbon from autotrophic plants via a common mycorrhizal fungus. Complex organic molecules, containing carbon, are to a minor extent also taken up from the soil by autotrophic plants. Soil-surface CO2 efflux accounts for roughly two-thirds of forest ecosystem respiration, and can be divided into heterotrophic and autotrophic components.
