Dynamique du carbone dans les communautés marécageuses à Cyperus papyrus L. (Cyperaceae) de la ville de Yaoundé et ses environs

Abstract

Cyperus papyrus L. is a Cyperaceaefoundall over Cameroon and isspecifically restricted in wetlands of Yaounde. The species occurs in monospecifical stand in Etang de la Retenue, Lac Municipal and Mvan-Ahala. It is of great ecological importance but knowledge of its natural dynamics on permanently flooded zones is limited.This workaims tostudy the influence ofenvironmental factorsoncarbon dynamicsin swampyC.papyruscommunitiesin Yaoundeand its icinities,throughobservations made indifferentwetlands microhabitats for three consecutive years from july 2007 to july 2010. Based on the microhabitats of the various wetlands, stratified sampling of delineated sitesconsisted of establishing plots of 10 m x 5 m, at the borders and on permanently wet areas. In these plots, the floristic surveys, monitoring of regeneration and floral phenology of C. papyrus were investigated. Destructive method of above and belowground biomass was used to quantify the carbon stocks of C. papyrus, as well as those of herbaceous plants harvested in swamps that were poor in C. papyrus. The evaluation of carbon stocks in soils (0-30 and 30-60 cm) was also undertaken. Forty-seven species of plants were identified in the swamps with C. papyrus. The results on monitoring the population dynamics indicated that C. papyrusconcentratesmostlyin permanently wet areas where vegetative regeneration is remarkable. This species also had affinities with highly anthropic environments, wet and slightly acidic soil. However, it should be noted that one of the essential characteristics of the regeneration dynamics of C. papyrus swamps in and around Yaounde is its dependence with regard to soil water. During the monitoring the floral phenology of C. papyrus, it was observed that the species flowers mainly during the dry season, thus it seems to follow a cycle with tropical characters. The precocity revealed inthe populatingof the compensating pond compared to the other sites can be explained based on differences in soil characteristics. With regards to biomass, swampswith C. papyrus (1,01 ± 0,34 kg MOC / m²) had a higher carbon stock than swamps with Rhynchospora corymbosa and Cyrtosperma senegalense ( 0,034 ± 0,01 kg MOC / m²) , as well as swamps with Echinochloa pyramidalis ( 0,026 ± 0,00 kg MOC / m²) . Also, regardless of the depth, stocks of soil carbon showed higher values for swamps with C. papyrus(66,25kg/m²). At the edges in contrast to permanently wet areas, carbon stocks are lower irrespective of the site. Generally, in the swamps with C. papyrus, carbon allocation is intended for soils with 90,18 % carbon; the litter and above and below ground compartments fixing 0,19 %, 4,06 % and 5,57 % respectively. In addition to biometric characteristics, some ecological factorsstrongly influence these carbon stocks: waterlogging, the depth of silt, pH, clay texture, and to a lesser extent, environmental pollution.