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 (Glomus hoi) were either allowed access to or excluded from Plantago lanceolata L. root litter embedded in soil; litter was labeled with either 13C only or 13C and 15N. Plant N uptake was significantly increased if AMF accessed the litter, and 15N analysis of the plant material indicated that 23% of plant N originated from litter. Succession of the soil community mediating decomposition was assessed by phospholipid fatty acids (PLFA) combined with 13C-PLFA. During the first 21 days of decomposition, saprotrophic fungi and Gram-negative bacteria were the dominant consumers of litter C. As decomposition progressed however, 13C content of the fungal biomarkers declined substantially, and Gram-negative and Gram-positive bacteria became the primary reservoirs of labeled litter C. The putative PLFA marker for AMF (16:1?5c) originated primarily from non-AMF sources. In AMF-invaded root litter, Gram-negative, Gram-positive, and 16:1?5c markers became less 13C-enriched relative to their counterparts in non-AMF-invaded microcosms during active decomposition. These patterns of 13C: 12C enrichment may result from AMF supply of 12C from the plant to the decomposing soil microbial community; such C inputs could alter the microbial mediation of litter decomposition.