Spatial characterization of arbuscular mycorrhizal fungal molecular diversity at the submetre scale in a temperate grassland

Although arbuscular mycorrhizal fungi (AMF) form spatially complex communities in terrestrial ecosystems, the scales at which this diversity manifests itself is poorly understood. This information is critical to the understanding of the role of AMF in plant community composition. We examined small-scale (submetre) variability of AMF community composition (terminal restriction fragment length polymorphism fingerprinting) and abundance (extraradical hyphal lengths) in two 1 m2 plots situated in a native grassland ecosystem of western Montana. Extraradical AMF hyphal lengths varied greatly between samples (14–89 m g soil−1) and exhibited spatial structure at scales <30 cm. The composition of AMF communities was also found to exhibit significant spatial autocorrelation, with correlogram analyses suggesting patchiness at scales <50 cm. Supportive of overall AMF community composition analyses, individual AMF ribotypes corresponding to specific phylogenetic groups exhibited distinct spatial autocorrelation. Our results demonstrate that AMF diversity and abundance can be spatially structured at scales of <1 m. Such small-scale heterogeneity in the soil suggests that establishing seedlings may be exposed to very different, location dependent AMF communities. Our results also have direct implications for representative sampling of AMF communities in the field

Suitability of mycorrhiza-defective mutant/wildtype plant pairs (Solanum lycopersicum L. cv Micro-Tom) to address questions in mycorrhizal soil ecology

Despite the importance of arbuscular mycorrhizal fungi (AMF) to ecosystem processes, few experimental tools are available to quantify AMF contributions to process rates. In this study we examine the efficacy of an experimental system consisting of wildtype (WT) and different non-mycorrhizal (Myc−) genotype pairs of tomato (Solanum lycopersicum L.), specifically focusing on cv Micro-Tom. Two conditions necessary to make such a system useful were examined; (1) that the Myc− genotype(s) do not get colonized in a full soil AMF community background, while the WT does, and B) that there are no non-target effects of the Myc− phenotype on soil microbes. We assessed the second condition by growing Myc− genotypes and WT in non-mycorrhizal soil, monitoring plant growth (root, shoot biomass; root length; root diameter size distribution) and soil microbial community structure (PLFA analysis) as indicators of any changes in root tissue quality or rhizodeposition. All tested Myc− genotypes showed a drastically reduced colonization in mycorrhizal soil. However, in non-mycorrhizal soil, M161 had greater root biomass and M20 greater microbial biomass compared to WT. Only one of the Myc− mutants examined fully met the criteria. We conclude that the BC1/WT pair is a powerful experimental system and recommend caution when using Myc− mutants in mycorrhizal ecology

Invasive plants rapidly reshape soil properties in a grassland ecosystem

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in mSystems 2 (2017): e00178-16, doi:10.1128/mSystems.00178-16.Plant invasions often reduce native plant diversity and increase net primary productivity. Invaded soils appear to differ from surrounding soils in ways that impede restoration of diverse native plant communities. We hypothesize that invader-mediated shifts in edaphic properties reproducibly alter soil microbial community structure and function. Here, we take a holistic approach, characterizing plant, prokaryotic, and fungal communities and soil physicochemical properties in field sites, invasion gradients, and experimental plots for three invasive plant species that cooccur in the Rocky Mountain West. Each invader had a unique impact on soil physicochemical properties. We found that invasions drove shifts in the abundances of specific microbial taxa, while overall belowground community structure and functional potential were fairly constant. Forb invaders were generally enriched in copiotrophic bacteria with higher 16S rRNA gene copy numbers and showed greater microbial carbohydrate and nitrogen metabolic potential. Older invasions had stronger effects on abiotic soil properties, indicative of multiyear successions. Overall, we show that plant invasions are idiosyncratic in their impact on soils and are directly responsible for driving reproducible shifts in the soil environment over multiyear time scales.Sean Gibbons was supported by an EPA STAR Graduate Fellowship and National Institutes of Health training grant 5T-32EB-009412. Other funding for this project was provided by MPG Ranch and DOE contract DE-AC02-06CH11357

<i>Poa secunda</i> local collections and commercial releases: A genotypic evaluation

<div><p>The genetics of native plants influence the success of ecological restoration, yet genetic variability of local seed collections and commercial seed releases remains unclear for most taxa. <i>Poa secunda</i>, a common native grass species in Intermountain West grasslands and a frequent component of restoration seed mixes, is one such species. Here, we evaluate the genetic variation of local <i>Poa secunda</i> collections in the context of wild populations and commercial seed releases. We evaluated AFLP markers for seven <i>Poa secunda</i> collections made over a 4000-hectare area and four commercial releases (High Plains, MT-1, Opportunity, and Sherman). We compare the genetic distance and distribution of genetic variation within and between local collections and commercial releases. The extent and patterns of genetic variation in our local collections indicate subtle site differences with most variation occurring within rather than between collections. Identical genetic matches were usually, but not always, found within 5 m² collection sites. Our results suggest that the genetic variation in two <i>Poa secunda</i> releases (High Plains and MT-1) is similar to our local collections. Our results affirm that guidelines for <i>Poa secunda</i> seed collection should follow recommendations for selfing species, by collecting from many sites over large individual sites.</p></div

Adapters and primers used in AFLP genotyping.

<p>Adapters and primers used in AFLP genotyping.</p

Local <i>Poa secunda</i> collection sites.

<p><i>Poa secunda</i> collection sites are indicated by white dots and letters. Approximately 20 plants were collected from each site. The red line outlines the boundary of MPG Ranch.</p

Distribution of variation within and between <i>Poa secunda</i> source identities.

<p>Distribution of variation within and between <i>Poa secunda</i> source identities.</p

<i>Poa secunda</i> commercial release source information.

<p><i>Poa secunda</i> commercial release source information.</p

<i>Poa secunda</i> genetic matches within and between local collections.

<p>Percentage of <i>Poa secunda</i> individuals with one or more genetic match within (black bars) or between (white bars) local <i>Poa secunda</i> collections. Pooled collections indicate variation in genetic matches within and between all collections and the overall percentage of individuals with one or more genetic match (gray bar).</p