Interactions between an arbuscular mycorrhizal fungus and a soil microbial community mediating litter decomposition

We investigated arbuscular mycorrhizal fungi ( AMF ) alteration of microbial mediation of litter decomposition. AMF ( G lomus hoi ) were either allowed access to or excluded from P lantago lanceolata L . root litter embedded in soil; litter was labeled with either 13 C only or 13 C and 15 N . Plant N uptake was significantly increased if AMF accessed the litter, and 15 N analysis of the plant material indicated that 2–3% of plant N originated from litter. Succession of the soil community mediating decomposition was assessed by phospholipid fatty acids ( PLFA ) combined with 13 C ‐ PLFA . During the first 21 days of decomposition, saprotrophic fungi and G ram‐negative bacteria were the dominant consumers of litter C . As decomposition progressed however, 13 C content of the fungal biomarkers declined substantially, and G ram‐negative and G ram‐positive bacteria became the primary reservoirs of labeled litter C . The putative PLFA marker for AMF (16:1ω5 c ) originated primarily from non‐ AMF sources. In AMF ‐invaded root litter, G ram‐negative, G ram‐positive, and 16:1ω5 c markers became less 13 C ‐enriched relative to their counterparts in non‐ AMF ‐invaded microcosms during active decomposition. These patterns of 13 C : 12 C enrichment may result from AMF supply of 12 C from the plant to the decomposing soil microbial community; such C inputs could alter the microbial mediation of litter decomposition.