Info

Glomus absent

2.34a

46.83b

Number of colony-forming units (CFU) was estimated on Nash_Snyder medium supplemented with benomyl, while quantitative PCR was used to quantify F. solani DNA. Different letters indicate that F. solani abundance, in the sampled soil compartment, differed significantly between the two Glomus treatments (data from Filion et al., 2003).

Number of colony-forming units (CFU) was estimated on Nash_Snyder medium supplemented with benomyl, while quantitative PCR was used to quantify F. solani DNA. Different letters indicate that F. solani abundance, in the sampled soil compartment, differed significantly between the two Glomus treatments (data from Filion et al., 2003).

abundance of AM fungi in soil, or by spore counts, which may overestimate the abundance of viable propagules.

Technological advances are aiding our understanding of plant_microbial mutualisms. Physiological and molecular markers (e.g., phospholipid fatty acids, proteins) allow for some resolution of microbial identity and abundance in soil and roots. Recent advances in the isolation and quantification of DNA from soil and plant tissue will be extremely valuable for studying the population and community dynamics of soil and root-associated microorganisms in real time. For example, Filion et al. (2003) developed a protocol using quantitative polymerase chain reaction (PCR) to study interactions between G. intraradices and F. solani. Using this protocol, plants inoculated with G. intraradices supported measurably reduced population levels of F. solani, corresponding to reductions in disease severity, that were not detected using culture-dependent techniques (Table 10.2). Soil community fingerprinting using PCR-based techniques (e.g., degrading-gradient gel electrophoresis, terminal restriction fragment length polymorphism) and comparing cloned gene sequences to existing sequence databases are other ways of characterizing microbial communities and determining how components of the soil community differ in response to different biotic and abiotic factors (Fig. 10.9).

conclusions

A diverse assemblage of plant-microbial mutualisms exists in the rhizosphere and rhizoplane. A primary focus of ecological research into plant-microbial mutualisms has been to understand the role that mutualistic symbioses play in promoting plant productivity. Recent research, however, has illuminated the fact that these symbioses likely function along a continuum, from mutualism to parasitism; this new view has enhanced our understanding of how plant communities are structured

FIGURE 10.9 Influence of (A) plant species and (B) soil treatment on the structuring of AM fungal communities, based on the similarity (maximum parsimony) of terminal restriction fragment length polymorphism profiles from individual roots of Agrostis capillaris, Poa pratensis, and Festuca rubra. Each terminal corresponds to the AM fungal community in a single root. Roots belonging to the same plant species were inhabited by similar AM fungal communities relative to those of other plant species. Soil treatment did not appear to have as great an effect on the AM fungal community as did host species. (Reprinted from Vandenkoornhuyse etal., 2003, with permission; copyright 2003, Blackwell Publishing.)

O Biocide

FIGURE 10.9 Influence of (A) plant species and (B) soil treatment on the structuring of AM fungal communities, based on the similarity (maximum parsimony) of terminal restriction fragment length polymorphism profiles from individual roots of Agrostis capillaris, Poa pratensis, and Festuca rubra. Each terminal corresponds to the AM fungal community in a single root. Roots belonging to the same plant species were inhabited by similar AM fungal communities relative to those of other plant species. Soil treatment did not appear to have as great an effect on the AM fungal community as did host species. (Reprinted from Vandenkoornhuyse etal., 2003, with permission; copyright 2003, Blackwell Publishing.)

and may affect how mutualistic symbioses are exploited in agriculture and forestry. The ubiquity of mutualistic symbioses in the rhizosphere and rhizoplane, as well as the high levels of microbial diversity and activity in general, guarantees that these regions are rich in interactions, many of which influence plant growth and fitness, community dynamics, and ecosystem functioning. A greater understanding of these interactions could allow us to better predict the effects of anthropogenic disturbances on the functioning of ecosystems and may lead to more effective microbial inoculants for use in agriculture and restoration. However, our ability to fully understand these interactions has been hampered by the opaque nature of the soil environment, the heterogeneity of soil, and the sheer number of linkages in these interactions. Also confounding matters is our inability to culture the majority of organisms present within the soil. New technologies show great promise for characterizing the composition of microbial communities associated with roots and soil and should allow us to resolve some of the interactions among mutualists, other soil organisms, and plants that are occurring in the soil environment.

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