DO MICROBES INFLUENCE SEED BANK DYNAMICS?

Authors: Chee Sanford, Joanne; Williams, Martin; Davis, Adam; Sims, Gerald

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2006
Publication Date: 6/1/2006
Citation: Chee Sanford, J.C., Williams, M., Davis, A.S., Sims, G.K. 2006. Do microbes influence seed bank dynamics? Weed Science. 54(3):575-587.

Interpretive Summary: Reduction of seed bank persistence is an important goal for integrated weed management systems. Recent interest in more biological-based weed management strategies has led to closer examination of the role of soil microorganisms. Laboratory studies demonstrate varying potential for seed decay among weed species, ranging from highly susceptible (velvetleaf), to very low susceptibility (giant ragweed). Regardless of whether seed decay is the outcome, the result can be that seeds are densely colonized by soil microorganisms. Microorganisms found associated with four weed species (woolly cupgrass, jimsonweed, Pennsylvania smartweed, and velvetleaf) were distinct from one another. The influence of seeds on microbial growth is hypothesized to be due to nutritional and surface attachment opportunities. With velvetleaf, a large diversity of bacteria can mediate seed decay, whereas fungal associations may be specific to weed species. Microbial decay of seeds presents clear opportunities for weed biocontrol, taking an approach that promotes the function of natural microbial enemies through habitat or cultural management. Understanding of the important soil factors is needed to enhance the activities of microorganisms of interest. The impact of this study is the finding that weed seeds of different species are subject to varying susceptibility to decay by natural soil microorganisms, and that specific biological and environmental factors control this activity in soil. Also, the apparent diversity of microbes that are involved in seed associations may be quite extensive.

Technical Abstract: Reduction of seed bank persistence is an important goal for integrated weed management systems. Recent interest in more biological-based weed management strategies has led to closer examination of the role of soil microorganisms. Seeds of many annual weeds can persist in soils, indicating the presence of yet unknown factors that regulate biological mechanisms of seed antagonism, including those associated with soil microorganisms. A fundamental understanding of interactions between seeds and microbes will have important implications for future weed management systems targeting seed banks. Herein we present current knowledge in this field, including new data. Laboratory studies demonstrate varying potential for seed decay among weed species, ranging from highly susceptible (velvetleaf), to very low susceptibility (giant ragweed). Microscopic examinations revealed dense microbial assemblages whenever seeds were exposed to colonization, regardless whether the outcome was decay. Microbial communities associated with seeds of four weed species (woolly cupgrass, jimsonweed, Pennsylvania smartweed, and velvetleaf) were distinct from one another. The influence of seeds on microbial growth is hypothesized to be due to nutritional and surface attachment opportunities. Closer examination of velvetleaf seeds suggests that diverse assemblages of bacteria can mediate decay, whereas fungal associations may be more limited and specific to weed species. Though microbial decay of seeds presents clear opportunities for weed biocontrol, limited success is met when exogenous microorganisms are introduced to natural systems. Alternatively, a conservation approach that promotes the function of indigenous natural enemies through habitat or cultural management may be more promising. A comprehensive ecological understanding of the system is needed to identify soil management methods that enhance the activities of microorganisms of interest. We describe some of the major challenges and opportunities encountered when studying the in situ relationships between seeds and microorganisms, and present examples of the approaches being taken by the ARS Invasive Weed Management Unit.