Experimental Study on the Role of Autumnshed Leaves in Aquatic Environments

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Abstract
Preliminary observations were made on the possible role of autumn-shed leaves of Ulmus americana, Alnus rugosa and Quercus alba in aquatic environment. The leaves were fed to Hyalella azteca, Asellus communis and Paraleptophlebia mollis. In all but one experiment there was a significant decrease in the percentage of protein in the unconsumed alder and oak leaves. The unconsumed elm leaves in all the experiments showed a highly significant increase in their protein content. Elm leaves left in an artificial stream also showed an increase, but alder and oak leaves showed a slight decrease. In some cases the increase in protein content perhaps represents an increase in the absolute quantity of nitrogen, as has been observed by some woodland ecologists in the decomposing leaf litter in forests. The results tend to indicate that the increase in the protein percentage in the elm leaves is not attributable to the bacterial population but is associated with the growth of the fungi. There is some sort of competition between the bacteria and the mycoflora developing on the leaves. The effect of temperature was highly significant in altering the protein content of the leaves. Some of the factors that are likely to influence the importance of autumn-shed leaves in aquatic environment are their composition, the type of microflora involved in their decomposition and the quality and temperature of water. In any study of the trophic structure of a body of water in which autumn-shed leaves are used as food, the microbial population deserves more consideration than it has received.

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