In this study, straw preservation effects of Arundo donax L. on its allelopathic activity to toxic and bloom-forming Microcystis aeruginosa were investigated. The aquatic extracts of fresh straw significantly inhibited the growth of M. aeruginosa. After 7 d of cultivation, the percentage inhibitions (PIs) of all treated groups were above 60% and the maximum almost reached 100%. However, when the straw was used after two-month preservation, its allelopathic activities decreased significantly with all PIs lower than 60%. To unclose the substance differences between fresh and long-time preserved straws, the contents of dissolved organic carbon (DOC) and ultraviolet-visible and fluorescence characteristics were analyzed. The results show that long-time preserved straw had lower DOC and UV254 values, weaker fluorescence intensities, and fluorescent substance loss. Further, the allelopathic fractions were isolated from the aquatic extracts of the straws by solvent extraction. The potential allelochemicals were analyzed by gas chromatography-mass spectrometry (GC-MS). The strong antialgal fractions of both fresh and long-time preserved straws were found to have various potential allelochemicals, including esters, ketones, alkaloids and phenolic acids. Their number was decreased from 21 to 9 after two-month preservation. The characteristics analysis of potential allelochemicals hinted that fresh A. donax might have more highly-effective allelochemicals than long-time preserved one.

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