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 (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 Gram-negative bacteria were the dominant consumers of litter C. As decomposition progressed however, (13) C 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 (16:1ω5c) originated primarily from non-AMF sources. In AMF-invaded root litter, Gram-negative, Gram-positive, and 16:1ω5c 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.