An experimental study of the breakdown of submerged leaves by hyphomycetes and invertebrates in Morocco

Abstract

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.

Invertebrate dynamics during the decomposition of dry and fresh willow leaves in Oued Zegzel (Eastern Morocco)

“…We believe that Hydropsyche maroccana would be better classified as both a shredder and a filterer. In fact, Chergui & Pattee (1991) reached the same conclusion following an experimental study : they found that the dried leaves of willow and oleander incubated in the presence of Hydropsyche maroccana lost 13 % and 8 % of their initial weight, respectively, in 30 days. In summer, Trichoptera dominated in the absence of any trophic competition.…”

“…The dependence of invertebrates activity on that of aquatic hyphomycetes was shown by Chergui & Pattee (1991) who found that the percentage of assimilation by Melanopsis praemorsa was greater when willow leaves were conditioned by Lemonniera aquatica. The percentage of assimilation was very low in the presence of Tetracladium marchalianum.…”

The breakdown of leaves of poplar and holm oak in three Moroccan streams : effect of burial in the sediment

“…The prosobranch gastropod Melanopsis, whose impact has been extensively demonstrated by Chergui & Pattee (1991a, 1991b, 1992, was dominant in the Sebou where it was present even in the deeper sediment strata. Thus faster breakdown in this site may be explained simultaneously by greater current velocity, coarser substratum, and their consequences: interstitial water flow, higher oxygen concentration, and the presence of shredders at all depths.…”

“…As the state in which most plant litter reaches the water in the semiarid Northeastern Moroccan climate is still uncertain (Chergui & Pattee 1991b), the leaves were dried to constant weight at 40 °C for 48 h, then weighed to the nearest 0.2 mg by batches of 2 or 3 g and enclosed in plastic bags until they were used.…”

Effects of Leaf Litter Species on Macroinvertebrate Colonization during Decomposition in a Portuguese Stream

“…Shredders in these streams may choose their food sources in function of their nutritional needs, and can feed preferentially on the leaves that are richer initially or that are enriched faster in terms of microbial colonization. When given a choice, shredders preferentially feed or colonize certain leaf species such as alder, or leaves there are already conditioned by microorganisms (CHERGUI and PATTEE, 1991;GRAÇA, 1992, 1995;GRAÇA et al, 1993;NOLEN and PEARSON, 1993). By incorporating leaves into secondary production, they accelerate leaf fragmentation and produce abundant fecal pellets, a source of FPOM to downstream invertebrates (GRAÇA, 2001).…”