Soil microbial and arbuscular mycorrhizal communities in afforested ecosystems of the Nebraska National Forest

The soil microbial community (SMC) links below- and above-ground process. By offering various benefits, arbuscular mycorrhizal fungi (AMF) promote plant growth. The Nebraska National Forest at Halsey (NNF), a hand-planted forest of dominantly Juniperus virginiana L and Pinus ponderosa, provides an ideal location to study the influence of vegetation changes on SMC structure and AMF diversity. Three research objectives were undertaken: (1) to determine the influence of afforestation on SMC structure at the NNF using fatty acid methyl ester (FAME) analysis; (2) to develop a denaturing gradient gel electrophoresis (DGGE)-cloning based method to characterize AMF community structure; and, (3) to characterize the diversity of AMF in roots of eastern red cedar (Juniperus virginiana L) invasive to grassland at the NNF. Although soil microbial biomass decreased with depth under the three vegetation types, microbial community composition at all depths reflected the current vegetation. Plant roots coupled with the downward movement of carbon may largely account for this similarity. Thus, plant species were more important controls on soil microbial community structure than physiochemical changes in soil properties with depth in the highly sandy parent materials of the NNF. Nested polymerase chain reaction (PCR) and DGGE were combined with cloning of fungal 18S ribosomal gene fragments for the rapid comparison of AMF community structure. Nested PCR-DGGE produced distinct banding patterns that provided non-subjective discrimination among samples. Construction of clone libraries enabled collection of reliable sequence information for bands of interest. The high throughput of DGGE combined with selected cloning makes this approach suitable for tracking AMF communities in ecological studies. The majority of the sequences obtained using this method were classified into Glomus group A. Roots of ERC seedlings harbor the most diverse AMF communities, which may foster the establishment of young seedling into grassland by tapping into existing AMF hyphal networks. AMF diversity in roots of ERC decreased with increasing stand age and canopy closure. Temporal changes in AMF community diversity may reflect different life histories and adaptive strategies of AMF species, and the interaction of biotic and abiotic factors with the expansion of ERC in grassland. Shifts in SMC structure and loss of AMF diversity on afforestation has impacted ecosystem services, such as carbon storage and nutrient cycling