The Fungal Community Associated with Seed of Giant Ragweed (Ambrosia trifida L.) in Soil.

Weed seed banks are the greatest sources of future annual weed infestation in crop systems. The high resilience, abundance, and persistence of seeds in soil of many annual weeds make weed control a continuing challenge. Knowledge of mechanisms affecting the mortality of weed seeds in soil is critical for development of long-term and sustainable weed management strategies. Microbe-mediated seed decay is thought to be an important cause of weed seed mortality in soil, however little information is known about the microbial populations or the mechanisms of decay. Artificial seed banks were used to examine the effect of depth, burial time, and related environmental factors on microbe-mediated seed decay of giant ragweed. The molecular-based analysis ARISA was used to characterize the fungal community associated with seed specimens. No seed decay occurred during the period from Dec. 2005 to Mar. 2006, but after four months of burial, the decay ratio increased over time up to the end of a one year time period. The effect of soil depth on seed decay was not significant, but did have a significant effect on the fungal community associated with seeds. Multidimensional scaling (MDS) analysis showed that the fungal community composition changed over time. Canonical Correspondence Analysis (CCA) of the data showed that temperature and soil moisture significantly influenced the fungal community composition on seeds during the growing season. The outcome of the study supported the hypothesis that microbial-mediated seed decay was an important cause of seed bank mortality. This research increases our understanding of the dynamics and mechanism of microbe- associated seed mortality of weed seeds in soil and provides useful information for development of future weed management strategies. Keywords: Soil Microorganisms, Seed decay, Giant Ragweed, Soil seed bank