The relative sensitivity of algae to decomposing barley straw

Decomposing barley straw has previously been shown to inhibit the growth of a limited number of algae under both laboratory and field conditions. Bioassays were conducted on a range of algae to evaluate their relative sensitivities to straw-derived inhibitor(s). A range of sensitivities was found, including some species that were resistant to the straw-derived inhibitor(s). A microcystin-producing strain of Microcystis aeruginosa was very susceptible to decomposing barley straw. Bioassays using Euglena gracilis suggest that the inhibitory compounds are not derived from the phototransformation of straw decomposition products and do not act primarily by inhibiting photosynthesis. Susceptibility to barley straw appears not to be related to general taxonomic or structural features. Possible implications for algal populations in natural freshwaters are briefly discussed.