•Soil seed bank characteristics depends on rainforest types (vegetation and soil).•Deep soil layers (up to 20 cm depth) have important seed stocks.•Each soil layer, including the 10–20 cm stratum, ...display exclusive taxa.•Similarity between pioneers of the soil seed bank and tree stand reaches 39–47%.•Timber tree taxa are lowly represented in the seed banks.
This study evaluates the characteristics of soil seed bank in two types of central African rainforests: Celtis forest on clay soils and Manilkara forest on sandy soils. In each study site, 30 samples were collected per soil layers (litter, 0–5 cm, 5–10 cm and 10–20 cm depth). The species diversity and abundance of the soil seed bank were estimated after soil samples were brought to germination. We globally observed 297 seedlings of 53 species for the Celtis forest and 222 seedlings of 39 species for the Manilkara forest. The total densities of germinated seeds were 330 seedlings m−2 and 247 seedlings m−2, respectively. Herbaceous species dominated with percentages of 41.0 and 45.3%, respectively in the Manilkara forest and the Celtis forest. Both forest types displayed a regeneration potential through the soil seed bank. However, this potential seems higher in the Celtis forest. Pioneer taxa were more abundant in the soil seed bank of the Celtis forest (13 woody pioneer species) than the Manilkara forest (9 woody pioneer species). The values of Sorensen similarity index between the standing tree vegetation and the soil seed bank in each site were relatively low: 11.0% for the Celtis forest and 8.8% for the Manilkara forest. But these similarity values were higher when only the pioneer species were considered: 46.8% in the Celtis forest and 38.9% in the Manilkara forest. The highest species richness were obtained in the first two soil layers (0–10 cm depth) while 21.8% and 21.4% of the species were exclusively found in the deepest layer (10–20 cm) in the Celtis forest and the Manilkara forest, respectively. Among the timber species found in the forest, only three were observed in the soil seed bank of the two sites: Nauclea diderrichii, Erythrophleum suaveolens and Staudtia kamerunensis. N. diderrichii was particularly abundant in the soil seed stock of the two sites (14.4–34.4 seeds m−2). Results suggested that to improve regeneration of timber species, planting in open forest habitats with seedlings coming from tree nursery should be more efficient.
In temperate regions the chemistry of the lower troposphere is known to be significantly affected by biogenic volatile organic compounds (VOCs) emitted by plants. The chemistry of the lower ...troposphere over the tropics, however, is poorly understood, in part because of the considerable uncertainties in VOC emissions from tropical ecosystems. Present global VOC models predict that base emissions of isoprene from tropical rainforests are considerably higher than from savannas. These global models of VOC emissions which rely mainly on species inventories are useful, but significant improvement might be made with more ecologically based models of VOC emissions by plants. Ecosystems along a successional transect from woodland savanna to primary rainforest in central Africa were characterized for species composition and vegetation abundance using ground surveys and remotely sensed data. A total of 336 species (mostly trees) at 13 sites were recorded, and 208 of these were measured for VOC emissions at near‐optimal light and temperature conditions using a leaf cuvette and hand‐held photoionization detector (PID). A subset of 59 species was also sampled using conventional VOC emission techniques in order to validate the PID technique. Results of ecological and VOC emission surveys indicate both phylogenetic and successional patterns along the savanna‐rainforest transect. Genera and families of trees which tend to emit isoprene include Lophira, Irvingia, Albizia, Artocarpus, Ficus, Pterocarpus, Caesalpiniaceae, Arecaceae, and Moraceae. Other taxa tend to contain stored VOCs (Annonaceae and Asteraceae). Successional patterns suggest that isoprene emissions are highest in the relatively early successional Isoberlinia forest communities and progressively decrease in the later successional secondary and primary rainforest communities. Stored VOCs appear to increase along the savanna‐rainforest succession, but these data are more tentative. These findings are consistent with successional patterns of isoprene and terpene fluxes in North American forests and highlight the feasibility of constructing better predictive models of VOC emissions.
The present study focused on the diuretic activity of the essential oil (EO) of Cymbopogon densiflorus(Steud.) Stapf and the citral (majoritaire compound). The analysis of the chemical composition of ...this oil bygas chromatography coupled with mass spectrometry (GC/MS) made it possible to identify several molecules.It emerges from this study that only EO at 150 mg/kg causes significant diuretic activity (V.U.E = 168.39%)such as furosemide; the latter being modest (V.U.E = 143.62%) for citral at a dose of 75 mg/kg. In treatedmice, removal of sodium was significant and potassium was spared compared to mice treated with distilledwater. The diuretic effect of EO of C. densiflorus leaves demonstrated in the present study is a mode of actionof this plant that justifies its use in traditional medicine against high blood pressure.
Lake Télé has a nearly perfect ellipsoidal shape and is surrounded by swamps and barely penetrable flooded forests in the heart of the Congo—Zaire watershed basin, and has intrigued the international ...scientific community for decades. In June 1992, a first Franco—Congolese multidisciplinary scientific expedition was finally able to reach the lake which is vast (23 km
2) and shallow (3 m). Its volume is estimated at 71 × 10
6m
3 and is 40% filled with an organic silt layer a metre thick. Its hydrological exchanges are almost exclusively vertical with very little lateral contribution from the surrounding swamp. This leads to the observation that the waters are very slightly mineralized (< 3 mg 1
−1), but are very rich in organic carbon (44% of suspended matter and of total dissolved matter) and are very acidic (pH < 4). In addition, a magnetic anomaly of some hundred nanoTesla from a magnetic body at shallow depth has been detected in the lake's northern half, although its origin remains unknown. Botanical and palynological observations suggest the persistence of a strongly hydromorphic forest environment for at least the last 6600 years. Identified pollen taxa, whether ancient or recent, come mainly from pioneer and colonizing taxa such as
Macaranga, which tends to indicate that the forest is continuing to gradually fill in the lake.
Le lac Télé, vaste lentille d'eau ellipsoïdale située au cœur de la forêt équatoriale du Nord-Congo, présente des échanges hydriques essentiellement verticaux qui confèrent une très faible ...minéralisation à ses eaux, par ailleurs très riches en carbone organique et très acides (pH < 4). Les observations palynologiques anciennes et récentes indiquent la pérennité d'un milieu forestier hydromorphe, durant au moins 6 600 ans. Son origine par impact météoritique est l'une des hypothèses pouvant expliquer l'anomalie magnétique du lac, qui continue à se refermer comme une lente cicatrisation sous la pression de la forêt environnante…
Lake Tele, a vast elliptic water body, located in the equatorial forest of north Congo, shows hydrological exchanges almost exclusively vertical, which are the reason for the low mineralisation of its waters. However, these are very rich in organic materials and highly acid (pH < 4). Palynological observations indicate that a highly hydromorphic forest environment persisted for… at least 6 600 years. One hypothesis for its origin suggests meteoric impact, which could explain its magnetic anomaly. The identified pollen species tend to show that this forest continues to progressively enclose the lake, like the slow closing-up of a scar.
PDF
