The influence of pH on concentrations of protein and phenolics and resource quality of decomposing floating leaf material of Nymphaea alba L. (Nymphaeaceae) for the detritivore Asellus aquaticus (L.).

Senescent floating leaf material of Nymphaea alba L., collected in an acidified moorland pool, was used in decomposition studies in two aquatic systems that differed greatly in pH, alkalinity and nutrient concentration. Concentrations of extractable protein and phenolics in the decomposing leaf material were measured during the incubation period. Protein levels were not significantly different in the leaf material from the two study sites, whereas the concentrations of phenolics in the degrading leaf blades from the acid site remained higher than in the material from the alkaline site. The resource quality of the decomposing leaf material was estimated by feeding tests using Asellus aquaticus (L.) in the laboratory. The effect of an artificially increased level of tannin on the feeding activity of A. aquaticus was also studied. Material from the acid system was consumed at a lower rate than material from the other system. The phenolic content of the material was found to be the most important feeding cue. The protein level of the leaf blade detritus seems to be of less importance. The structure of the decomposing leaf blades may have influenced the resource quality in the later stages of the experiment.