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1. Mechanisms of the breakdown of submerged leaves under the warm and dry Moroccan climate, including the interaction between hyphomycetes and invertebrates, were investigated.2. Laboratory experiments were performed on dried leaves of Salix sp. and Nerium oleander.3. During the first month under the experimental conditions, Melanopsis praemorsa, Physa acuta (Gastropoda) and Hydropsyche maroccana (Trichoptera), respectively, were responsible for a loss of weight of 38, 21 and 13% in willow leaves, and 40, 15 and 8% in oleander leaves.4. The weight lost by willow leaves inoculated with the fungi Alatospora acuminata, Anguillospora longissima, Lemonniera aquatica and Tetracladium marchalianum increased with time, but varied according to the fungal species. Loss of weight and increase in nitrate and phosphate content of the leaves were greatest with Lemonniera and smallest with Tetracladium. 5. When the leaves thus colonized by each of the four fungal species were exposed to each of the three invertebrates, the amount of material consumed increased with the time of fungal conditioning and varied according to the fungus and to the invertebrate. Greatest consumption was by Melanopsis feeding on leaves conditioned by Lemonniera., in which case assimilation percentage by the gastropod was as high as 75%.6. Owing to their numbers in the field, and to the quantity of leaf material they ingest, gastropods appear as the main shredders in the streams considered, thus replacing the Crustacea that often play this part under temperate climates. Breakdown seems faster in Morocco than in France, mainly because of a shorter initial time lag in weight loss.

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OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 16130To link to this article :

Breakdown rate of terrestrial and aquatic leaves was found to depend on leaf species and on the biotope considered.As the leaves started decaying at different dates and had different breakdown rates, consumable allochthonous or autochthonous organic matter was fed t o the aquatic system throughout the year, from one summer t o the next.A comparison with former results on the main channel confirms the existence of a transversal gradient in the fluvid network: under the influence of fungal and invertebrate colonization, breakdown was fastest in the channel of the river, slower in an open side-arm, and slower still in a more lateral and closed side arm, in which organic matter accumulated in hypoxic conditions. Contents