Submitted to: Microbial Ecology International Symposium
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/4/2004
Publication Date: 8/22/2004
Citation: Chee-Sanford, J.C., Connor, L.M., Holman, T.J., Williams, M.M., Sims, G.K. 2004. Interactions between microorganisms and weed seeds: novel implications for the microbe relationships. [abstract]. American Society for Microbiology. Paper No. N-114. Interpretive Summary: Buried seed reserves in soil (seed banks) are a major source of future plant emergence. Seed production from many annual weed species is high and the longevity of seed banks suggests existing mechanisms of seed protection. The role of microorganisms in seed fate is poorly described, as are seed bank factors influencing microbial growth, survival, or seed associations. More specifically, we need to know if there are particular microorganisms associated with seeds of different species of weed, and if these microbial populations affect weed survival, persistence, and success. In this study, we examined microbial populations associated with seeds of the common weeds velvetleaf, giant ragweed, Pennsylvania smartweed, jimsonweed, and woolly cupgrass after exposure of the seeds to soil microorganisms. Velvetleaf seeds were extensively decayed after three months, while most seeds of the other weed species tested were not. Genetic analysis indicated certain microbial species may be correlated to individual weed species, but these differed depending on the original soil community the seeds were exposed to. The results of this study suggests that different species of weeds undergo a range in the extent of loss due to seed decay processes, and further, while the potential for seed decay can be widely distributed in many soils, the extent of seed decay under natural conditions in the soil may be far less extensive and due to factors that are currently undefined.
Technical Abstract: Buried seed reserves in soil (seed banks) are a major source of future plant emergence. Seed production from many annual weed species is high and the longevity of seed banks suggests existing mechanisms of seed protection. The role of microorganisms in seed fate is poorly described, as are seed bank factors influencing microbial growth, survival, or seed associations. In this study, we characterized microbial populations associated with seeds of weed species (velvetleaf, giant ragweed, Pennsylvania smartweed, jimsonweed, woolly cupgrass) as affected by exposure to soil inocula. With the exception of velvetleaf, seeds resisted decay during three months exposure to soil microorganisms. Terminal restriction fragment and rDNA sequence analysis indicated correlations between seed associated community structure and soil type. Within a soil, however, common taxa and closely related microbial species were present on replicate seeds, suggesting specific plant-microbe relationships. Few fungi and bacteria were detected microscopically or by PCR on surfaces of seeds collected directly from plants, but abundant growth and diversity of both fungi and bacteria were found on seeds incubated with soil-derived inocula. Major bacterial phylotypes found were Bacteroidetes and subclasses of Proteobacteria. Primary fungal phylotypes included members of Ascomycota and Basidiomycota. The results suggest seeds may provide a selective environment for microbial associations, and for certain weed species, the potential for seed decay by microorganisms is widespread but somehow limited in natural soil. This study investigates an aspect of the fundamental relationships between microorganisms and weed seeds, with broader implications for soil seed bank ecology in natural systems.