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John N Klironomos

Publications and source records attributed to John N Klironomos.

13 recordsLinked to original sources
PubMed2006

Small-scale spatial heterogeneity of arbuscular mycorrhizal fungal abundance and community composition in a wetland plant community.

Although it has become increasingly clear that arbuscular mycorrhizal fungi (AMF) play important roles in population, community, and ecosystem ecology, there is limited information on the spatial structure of the community composition of AMF in the field. We assessed small-scale spatial variation in the abundance and molecular diversity of AMF in a calcareous fen, where strong underlying environmental gradients such as depth to water table may influence AMF. Throughout an intensively sampled 2 x 2 m plot, we assessed AMF inoculum potential at a depth of 0-6 and 6-12 cm and molecular diversity of the AMF community using terminal restriction fragment length polymorphism of 18S rDNA. Inoculum potential was only significantly spatially autocorrelated at a depth of 6-12 cm and was significantly positively correlated with depth to water table at both depths. Molecular diversity of the AMF community was highly variable within the plot, ranging from 2-14 terminal restriction fragments (T-RFs) per core, but the number of T-RFs did not relate to water table or plant species richness. Plant community composition was spatially autocorrelated at small scales, but AMF community composition showed no significant spatial autocorrelation. Saturated soils of calcareous fens contain many infective AMF propagules and the abundance and diversity of AMF inoculum is patchy over small spatial scales.

DNA, Fungal↗
PubMed2006

Invasive plant suppresses the growth of native tree seedlings by disrupting belowground mutualisms.

The impact of exotic species on native organisms is widely acknowledged, but poorly understood. Very few studies have empirically investigated how invading plants may alter delicate ecological interactions among resident species in the invaded range. We present novel evidence that antifungal phytochemistry of the invasive plant, Alliaria petiolata, a European invader of North American forests, suppresses native plant growth by disrupting mutualistic associations between native canopy tree seedlings and belowground arbuscular mycorrhizal fungi. Our results elucidate an indirect mechanism by which invasive plants can impact native flora, and may help explain how this plant successfully invades relatively undisturbed forest habitat.

Brassicaceae↗
PubMed2006

Biotic interactions and plant invasions.

Introduced plant populations lose interactions with enemies, mutualists and competitors from their native ranges, and gain interactions with new species, under new abiotic conditions. From a biogeographical perspective, differences in the assemblage of interacting species, as well as in abiotic conditions, may explain the demographic success of the introduced plant populations relative to conspecifics in their native range. Within invaded communities, the new interactions and conditions experienced by the invader may influence both its demographic success and its effects on native biodiversity. Here, we examine indirect effects involving enemies, mutualists and competitors of introduced plants, and effects of abiotic conditions on biotic interactions. We then synthesize ideas building on Darwin's idea that the kinds of new interactions gained by an introduced population will depend on its relatedness to native populations. This yields a heuristic framework to explain how biotic interactions and abiotic conditions influence invader success. We conclude that species introductions generally alter plants' interactions with enemies, mutualists and competitors, and that there is increasing evidence that these altered interactions jointly influence the success of introduced populations.

Animals↗
PubMed2006

The promise and the potential consequences of the global transport of mycorrhizal fungal inoculum.

Advances in ecology during the past decade have led to a much more detailed understanding of the potential negative consequences of species' introductions. Moreover, recent studies of mycorrhizal symbionts have led to an increased knowledge of the potential utility of fungal inoculations in agricultural, horticultural and ecological management. The intentional movement of mycorrhizal fungal species is growing, but the concomitant potential for negative ecological consequences of invasions by mycorrhizal fungi is poorly understood. We assess the degree to which introductions of mycorrhizal fungi may lead to unintended negative, and potentially costly, consequences. Our purpose is to make recommendations regarding appropriate management guidelines and highlight top priority research needs. Given the difficulty in discerning invasive species problems associated with mycorrhizal inoculations, we recommend the following. First, careful assessment documenting the need for inoculation, and the likelihood of success, should be conducted prior to inoculation because inoculations are not universally beneficial. Second, invasive species problems are costly and often impossible to control by the time they are recognized. We recommend using local inoculum sources whenever possible. Third, non-sterile cultures of inoculum can result in the movement of saprobes and pathogens as well as mutualists. We recommend using material that has been produced through sterile culture when local inoculum is not available. Finally, life-history characteristics of inoculated fungi may provide general guidelines relative to the likelihood of establishment and spread. We recommend that, when using non-local fungi, managers choose fungal taxa that carry life-history traits that may minimize the likelihood of deleterious invasive species problems. Additional research is needed on the potential of mycorrhizal fungi to spread to non-target areas and cause ecological damage.

Agriculture↗
PubMed2006

Phylogeny of arbuscular mycorrhizal fungi predicts community composition of symbiosis-associated bacteria.

Many physicochemical and biotic aspects of the soil environment determine the community composition of bacteria. In this study, we examined the effects of arbuscular mycorrhizal fungi, common symbionts of higher plants, on the composition of bacterial communities after long-term (7-8 years) enrichment culture in the presence of a plant host. We showed that the phylogeny of arbuscular mycorrhizal fungal isolates was a highly significant predictor of bacterial community composition, as assessed by cluster analysis, redundancy analysis and linear discriminant analysis of phospholipid fatty acid patterns. Numerous phospholipid fatty acids differed between the phylogenetic groupings; this pattern also held for fungal-origin phospholipid fatty acids and in a combined bacterial/fungal analysis, suggesting that categorizing phospholipid fatty acids into predominantly bacterial and fungal origin did not affect the overall outcome. The mechanisms underlying this observation could include substrate quality (and quantity) effects, interactions mediated by the host plant (e.g. rhizodeposition) and direct biotic interactions between arbuscular mycorrhizal fungi and bacterial populations. Our results suggest that aspects of arbuscular mycorrhizal fungal functions may be partially explained by the symbiosis-accompanying bacterial communities, a possibility that should be explicitly considered in studies examining the roles of arbuscular mycorrhizal fungal species diversity in soil and ecosystem processes.

Bacteria↗
PubMed2005

Quantitation of transgenic plant DNA in leachate water: real-time polymerase chain reaction analysis.

Roundup Ready (RR) genetically modified (GM) corn and soybean comprise a large portion of the annual planted acreage of GM crops. Plant growth and subsequent plant decomposition introduce the recombinant DNA (rDNA) into the soil environment, where its fate has not been completely researched. Little is known of the temporal and spatial distribution of plant-derived rDNA in the soil environment and in situ transport of plant DNA by leachate water has not been studied before. The objectives of this study were to determine whether sufficient quantities of plant rDNA were released by roots during growth and early decomposition to be detected in water collected after percolating through a soil profile and to determine the influence of temperature on DNA persistence in the leachate water. Individual plants of RR corn and RR soybean were grown in modified cylinders in a growth room, and the cylinders were flushed with rain water weekly. Immediately after collection, the leachate was subjected to DNA purification followed by rDNA quantification using real-time Polymerase Chain Reaction (PCR) analysis. To test the effects of temperature on plant DNA persistence in leachate water, water samples were spiked with known quantities of RR soybean or RR corn genomic DNA and DNA persistence was examined at 5, 15, and 25 degrees C. Differences in the amounts and temporal distributions of root-derived rDNA were observed between corn and soybean plants. The results suggest that rainfall events may distribute plant DNA throughout the soil and into leachate water. Half-lives of plant DNA in leachate water ranged from 1.2 to 26.7 h, and persistence was greater at colder temperatures (5 and 15 degrees C).

DNA, Plant↗
PubMed2005

Abrupt rise in atmospheric CO2 overestimates community response in a model plant-soil system.

Attempts to understand the ecological effect of increasing atmospheric CO2 concentration, [CO2], usually involve exposing today's ecosystems to expected future [CO2] levels. However, a major assumption of these approaches has not been tested--that exposing ecosystems to a single-step increase in [CO2] will yield similar responses to those of a gradual increase over several decades. We tested this assumption on a mycorrhizal fungal community over a period of six years. [CO2] was either increased abruptly, as is typical of most [CO2] experiments, or more gradually over 21 generations. The two approaches resulted in different structural and functional community responses to increased [CO2]. Some fungi were sensitive to the carbon pulse of the abrupt [CO2] treatment. This resulted in an immediate decline in fungal species richness and a significant change in mycorrhizal functioning. The magnitude of changes in fungal diversity and functioning in response to gradually increasing [CO2] was smaller, and not significantly different to those with ambient [CO2]. Our results suggest that studies may overestimate some community responses to increasing [CO2] because biota may be sensitive to ecosystem changes that occur as a result of abrupt increases.

Analysis of Variance↗
PubMed2005

The effects of perennial ryegrass and alfalfa on microbial abundance and diversity in petroleum contaminated soil.

Enhanced rhizosphere degradation uses plants to stimulate the rhizosphere microbial community to degrade organic contaminants. We measured changes in microbial communities caused by the addition of two species of plants in a soil contaminated with 31,000 ppm of total petroleum hydrocarbons. Perennial ryegrass and/or alfalfa increased the number of rhizosphere bacteria in the hydrocarbon-contaminated soil. These plants also increased the number of bacteria capable of petroleum degradation as estimated by the most probable number (MPN) method. Eco-Biolog plates did not detect changes in metabolic diversity between bulk and rhizosphere samples but denaturing gradient gel electrophoresis (DGGE) analysis of PCR-amplified partial 16S rDNA sequences indicated a shift in the bacterial community in the rhizosphere samples. Dice coefficient matrices derived from DGGE profiles showed similarities between the rhizospheres of alfalfa and perennial ryegrass/alfalfa mixture in the contaminated soil at week seven. Perennial ryegrass and perennial ryegrass/alfalfa mixture caused the greatest change in the rhizosphere bacterial community as determined by DGGE analysis. We concluded that plants altered the microbial population; these changes were plant-specific and could contribute to degradation of petroleum hydrocarbons in contaminated soil.

Bacteria↗
PubMed2004

Ecological linkages between aboveground and belowground biota.

All terrestrial ecosystems consist of aboveground and belowground components that interact to influence community- and ecosystem-level processes and properties. Here we show how these components are closely interlinked at the community level, reinforced by a greater degree of specificity between plants and soil organisms than has been previously supposed. As such, aboveground and belowground communities can be powerful mutual drivers, with both positive and negative feedbacks. A combined aboveground-belowground approach to community and ecosystem ecology is enhancing our understanding of the regulation and functional significance of biodiversity and of the environmental impacts of human-induced global change phenomena.

Animals↗
PubMed2004

Methods of studying soil microbial diversity.

Soil microorganisms, such as bacteria and fungi, play central roles in soil fertility and promoting plant health. This review examines and compares the various methods used to study microbial diversity in soil.

Bacteria↗
PubMed2002

Feedback with soil biota contributes to plant rarity and invasiveness in communities.

Understanding the relative abundance of species in plant communities is an unsolved problem. Mechanisms such as competition, resource partitioning, dispersal ability and predation tolerance do not adequately explain relative abundance under field conditions. Recent work suggests that interactions between plants and soil microbes is important. Here I show that such interaction explains a significant proportion of the variance in the relative abundance of species in plant communities. Rare plants exhibited a relative decrease in growth on 'home' soil in which pathogens had had a chance to accumulate, whereas invasive plants benefited from interactions with mycorrhizal fungi. Some plant species accumulate pathogens quickly and maintain low densities as a result of the accumulation of species-specific pathogens, whereas others accumulate species-specific pathogens more slowly and do not experience negative feedback until plant densities reach high levels. These results indicate that plants have different abilities to influence their abundance by changing the structure of their soil communities, and that this is an important regulator of plant community structure.

Canada↗
PubMed2002

Colonization of roots by arbuscular mycorrhizal fungi using different sources of inoculum.

Arbuscular mycorrhizal fungi (AMF) form a number of different infective propagules that are used to form new mycorrhizal associations. These are spores, extraradical hyphae and infected roots. However, not all fungi are equally capable of colonizing roots with all of the above-mentioned propagules and there is conflicting evidence of major differences in colonization strategy between members of the Glomineae and Gigasporineae. In this study, we tested the abilities of eight fungal species from four different genera to colonize roots using three different types of inoculum. Glomus and Acaulospora isolates colonized from all inoculum types, whereas Gigaspora and Scutellospora isolates colonized mainly from spores and to a limited degree from root fragments. Extraradical hyphae were not suitable propagules for the species of Gigaspora and Scutellospora tested. This indicates that AMF have different colonization strategies and that this is largely differentiated at the suborder level. It is unclear why there is such a difference among the fungi in inoculum types. Future research should examine differences in the anatomy and physiology to discern a mechanism for such differences in life-history strategies.

Ascomycota↗