Investigating the Role of Microorganisms in Soil Seed Bank Management

Authors: Chee Sanford, Joanne; FU, XIANHUI - UNIVERSITY OF ILLINOIS

Submitted to: Current Research, Technology and Education Topics in Applied Microbiology and Microbial Biotechnology
Publication Type: Book / Chapter
Publication Acceptance Date: 7/2/2010
Publication Date: 12/1/2010
Citation: Chee Sanford, J.C., Fu, X. 2010. Investigating the Role of Microorganisms in Soil Seed Bank Management. In: Mendez-Vilas, J., editor. Current Research, Technology and Education Topics in Applied Microbiology and Microbial Biotechnology. Badajoz, Spain: FORMATEX. p. 257-266.

Interpretive Summary: Interest in understanding seed bank processes aimed toward land management and weed control requires new information that integrates methodological approaches that include both plant and microorganisms. Development of experimental approaches that allow a more comprehensive analysis of seeds and associated microbes require procedures that result in meaningful interpretation, which have not previously been done in seed bank studies. We present a general overview of an experimental approach using artificial seed bank constructs that incorporate more stringent procedures for molecular microbial analyses for both seeds and soil, and discuss the importance of obtaining a metadata set that includes microbial characterization, seed characterization, measurements of environmental parameters, and the use of multivariate statistics as the most suitable method to analyze large data sets. We demonstrate concepts using an artificial seed bank study conducted with giant ragweed, an annual species that is problematic in Midwest cropping systems. Data from the study is used to show the application of new experimental approaches, which has applicability to studies with other types of seed banks, including forest and wetlands.

Technical Abstract: The soil seed bank plays an important role in the natural environment of many ecosystems, functioning as natural seed reserves for future regeneration of many plant species. Arable weed seed banks were first studied intensively because of their important economic impacts in agricultural systems. More recently, there has been heightened interest in the role of seed banks for restoration ecology in a variety of natural areas such as forests and wetlands following disturbances. Seed mortality in soil is one of the key factors for the persistence and density fluctuations of plant populations, especially for annual plants. A number of soil microorganisms are known for their important relationships with plants, including seedling development and giving rise to numerous rhizosphere processes and disease protection. The role of microorganisms as important regulators of seed banks, however, is not well-studied. In light of expanding knowlege about soil microbial diversity, we can hypothesize the many roles that natural populations of soil microorganisms may have in relationship to seeds, with consequent effects on seed mortality and plant development. Fungi in particular, have been implicated in seed decay of some plant species, yet little is understood about the extent of the populations involved and the mechanisms of interaction. In this study, we present an approach to examine microbial populations associated with seeds following soil burial over time. An artificial seed bank system was constructed and the burial was conducted at an agricultural field site in northern Illinois. Seeds of giant ragweed (Ambrosia trifida L.), a summer annual species with a persistent seed bank found widespread in the U.S., underwent seed bank losses attributed to germination and decay. Using PCR-based community profiles of fungi (ARISA) obtained from recovered seed specimens taken during seasonal time points, we applied multivariate statistical analyses to the data to determine if there were characteristic microbial populations specifically associated with the outcomes of germination or decay. In the early spring when seed germination was highest, fungal populations were more similar among seeds recovered during the early stage of radicle emergence. In the early to late summer and fall seasons, seeds that underwent presumed fatal germination resulted in microbial communities more similar to seeds that underwent direct decay. Microbial communties shifted over burial time suggesting successional colonization patterns, ultimately resulting in mixed saprophytic populations growing at the expense of decaying seeds. High magnification microscopic examination of seeds indicated instances of direct microbial adhesion to seed surfaces. These results suggest that characteristic microbial populations that originate from the extant soil community form associations with seeds, and the nature of these associations may play a role in the outcome of seed fate. The experimental approaches used in this study can be more broadly extended to other plant species and ecosystems of interest and provide new knowledge regarding seed-microbe interactions that can aid more effective management of seed banks.