The carbon origin of arbuscular mycorrhizal fungi estimated from δ 13 C values of individual spores

Abstract

The origin of carbon in the spores of arbuscular mycorrhizal (AM) fungi was quantified based on their obligate symbiosis with C3 and C4 plants showing clearly different δ13C values. The δ13C values of individual spores of the AM fungus Gigaspora margarita were analyzed. In monoculture pots of a C3 or a C4 plant species, spore δ13C values were ca. 3.5‰ lower than those of host roots. In coculture pots of a C3 and a C4 plant species, spore δ13C values varied between those of the roots of C3 and C4 plants, and increased linearly from the C3 to the proximity of the C4 plant (P<0.01). This reflects the higher δ13C values in C4 plants than in C3 plants. Thus the carbon origin of G. margarita spores changed with growth state and combination of host plants. In the presence of fresh plant residue instead of living host plants, spore δ13C values did not vary with distance from the residue. This finding supports the current view that AM fungi are obligate symbionts.