RÉSUMÉ
The study estimated the decomposition rate and nutrient dynamics of the litter of three riparian tree species; Mortis nigra L. [Moraceac], and Salix tetrasperma Roxb. and Populus alba L. [Salicaceae]. Dead fallen leaves of the studied species were collected from the banks of El-Khamseen canal; an ultimate Nile branch passing along Saft El-Laban town, Giza Governorate, Egypt. The amount of nutrients released back into eater after the decomposition of the dead leaves' tissues was investigated in plastic tanks located in the ecology lab of Botany Department of Cairo University, at the window side under natural conditions. The litterbag technique was followed. The species detritus decomposition was studied during the autumn season from September 25 to November 25], 2014. In order to determine the decay rates, litterbags [1.5 mm] were applied and collected at seven times intervals for three replications, each. All samples were dried, weighed and analyzed for total soluble sugars, P, N, ash and lignin concentrations. Decomposition of Morus leaf litters A as faster than that of the other two species due to its high quality [lower lignin, higher P and moderate N and total soluble sugars contents], in comparison to other species. More than 50% of the initial leaf masses of the study species were decomposed during two months. The difference in decay rate was affected by the ratios: C/N, C/P, lignin /N and lignin /P. The variation in the microbial activities caused fluctuations in the liter nutrient concentrations and the nutrient content remaining. Bacterial and fungal counts differed on the surfaces of the remaining masses depending on the variation in P and N concentrations. Leaf litter decay of species was mainly dependent on bacterial counts that ranged between limited numbers to uncountable than on fungi. Suitable thermal and aerobic conditions contributed to the explanation of the high decay of the species. There was a strong positive correlation between the species and mass remaining, species and N content remaining and between all nutrient concentrations and all nutrient content remaining. No positive relation was found between harvest time and sugar, P and N content remaining. The leaf litter extracts affected the seed germination of Eruca sativa. Moreover, the extracts caused root growth inhibition and promoted the shoot growth of the seedlings