Towards Understanding the Nature of Algal Inhibitors from Barley Straw

Abstract

The algal inhibitors released from barley straw decomposing in water and providing the basis for its use in algal control could be either of microbial origin or derived from straw components. We report here that unrotted straw releases algal inhibitors if finely chopped or autoclaved, providing further support for the view that straw, and not microbial colonists, is the primary source of inhibitors. Further support is also provided for the suggestion that inhibitors are or derive from oxidised lignin. Comparisons of lignin-enriched wood (brown-rotted) with lignin-depleted wood (white-rotted) from various deciduous trees show high antialgal activity of the former and little or no activity of the latter. Preliminary studies have shown that solubilised lignin is present in the liquor from rotted barley straw and brown-rotted wood. Since, however, the antialgal effects of deciduous leaf litter appear to depend initially on release of tannins and given that alkaline, oxidising conditions are usually essential for antialgal activity, it is proposed that oxidised polyphenolics, derived from lignin or tannins, are a source of algal inhibitors from plant litter.