Caractéristiques et stock de carbone de la végétation ligneuse des systèmes d’utilisation des terres de la commune de Coumbacara (Kolda, Sénégal)

Forest degradation causes carbon loss and indirectly contributes to climate change. Thus, the objective of this study is to assess the contribution of land use systems in the commune of Coumbacara to climate change mitigation through an estimate of woody diversity and their carbon stock. Thus, an inventory of woody vegetation was carried out on 72 plots of 30 m x 30 m in the forests adjacent to the fields and 50 m x 50 m in the hut and bush fields. The measurements related to the total height (m), the diameter at breast height (DBH) ≥ 10 cm and the crown diameter (m) of individuals of woody species. In addition to the diversity of this vegetation, the dendrometric data collected made it possible to develop the structure of woody vegetation, to estimate aboveground and belowground biomass as well as carbon stocks using allometric equations. In the forests adjacent to the fields, Combretaceae (61.9%) and Mimosaceae (52.4%) dominate. The woody population of this land use system has a decreasing exponential type structure with a specific richness of 7.85 ± 3.48 species and a density of 4.92 ± 0.39 feet/ha. The carbon stored there rises respectively by 1.57± 0.19 tC/ha for the aboveground biomass and 1.58±0.57 tC/ha for the belowground biomass. At the level of bush fields and hut fields, Anacardiaceae and Malvaceae are the most frequent. These agroforestry systems have a decreasing exponential type structure for the bush fields and an irregular structure for the hut fields. The bush fields have a species richness of 3.31±1.82 against 1.63±1.09 species for the hut fields. The density there is 3.01±0.57 feet/ha (bush fields) and 1.89±0.65 feet/ha (home fields). In addition, the amounts of carbon stored in the aboveground biomass of these systems are respectively 1.05 ±0.3 tC/ha and 0.99 ±0.51 tC/ha for the bush and hut fields against 0. 51±0.37 tC/ha and 0.54±0.49 tC/ha for underground woody biomass

Functional groups of Sahelian trees in a semiarid agroforestry system of Senegal

Aims Addressing plant responses to water stress is critical to understand the structure of plant communities in water-limited environments and to forecast their resilience to future changes in climate. In a semiarid agroforestry system in the Sahelian savannah of Leona (Senegal), we selected nine common tree species and explored their stress-resistance mechanisms. These species represent a variety of life forms and are of high regional socio-economic importance. We hypothesized that different species would show different suites of traits to cope with water stress and expected to identify functional groups differing in strategies to withstand water shortage. Methods Along a dry and a wet season, we monitored four traits reflecting above- and below-ground strategies of resource acquisition such as predawn leaf water potential (ψpd), specific leaf area (SLA), leaf thickness and leaf area index (LAI). We also measured two morphological traits: trunk diameter and tree height. LAI and ψpd were measured six times during the dry and rainy seasons, and the other traits were measured once. Important Findings We identified two functional classes subdivided into two functional groups of each class. The first class included deciduous and semi-deciduous species that generally had large SLA, low leaf thickness and small-to-intermediate inter-seasonal variations in ψpd. The second class included evergreen species of two functional groups that differ in SLA, leaf thickness and the magnitude of inter-seasonal variations of ψpd throughout the year. The four functional groups identified in this study represent plant strategies differing in their response to changing environmental conditions. Keywords: Acacia tortilis, Adansonia digitata, Balanites aegyptiaca, Celtis integrifolia, Combretum glutinosum, Faidherbia albida, functional traits, Neocarya macrophyla, Sclerocarya birrea, Tamarindus indica, water stressacceptedVersio

Carbonic anhydrase and ribulose 1,5-bisphosphate regulate ribulose 1,5-bisphosphate carboxylase/oxygenase affinity for carbon dioxide

The carboxylase activity of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) was assayed in cowpea (Vigna unguiculata [L.] Walp. var. Bambey 21), a C3 plant, with or without carbonic anhydrase (CA) and ribulose 1,5-bisphosphate (RuBP) added to the reaction mixtures. The apparent K(m) (CO2) and V(max) were determined using the statistical formula of Wilkinson and by the direct linear plot method of Cornish-Bowden and Eisenthal. During the experiments, V(max) remained constant whereas K(m) changed according to the assay conditions. It was found that K(m) (CO2) of Rubisco decreased below the commonly accepted value in the absence of added CA and with high concentrations of RuBP. The variations of K(m) were discussed on the basis of the relative implication of RuBP and CA in the carboxylase activity. The practical applications of these experiments were also highlighted.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Germination, growth and physiological responses of Senegalia senegal (L.) Britton, Vachellia seyal (Delile) P. Hurter and Prosopis juliflora (Swartz) DC to salinity stress in greenhouse conditions

Salinity is among the most widespread environmental threats to global plant  production, especially in arid and semi-arid climates. Thus, the selection of salt tolerant species is necessary for sustainable plant productivity. The purpose of this study was to measure and understand the salt tolerance of three multipurpose trees used in reforestation programs in many Sahelian countries (Senegalia senegal, Syn. Acacia senegal; Vachellia seyal, Syn. A. seyal, and Prosopis juliflora). The effect of salinity was evaluated at seed germination stage on Petri dishes containing water agar (0.9%, w/v) with seven concentrations of NaCl (0, 86, 171, 257, 342, 428, and 514 mM). Our results showed that all the species had a germination rate higher than 85% at 257 mM. However, it decreased at 342 mM with a reduction of 70 and 20%, respectively for S. senegal and V. seyal. For plants growth and physiological responses, seedlings were individually cultivated in plastic bags (25×12 cm) containing non-sterile soil and watered with four salt solutions (0, 86, 171 and 257 mM NaCl). Four months after the plants’ cultivation, the results showed that for all species, the salinity reduced significantly the height, the collar diameter, the shoot and root dry biomass as well as the total chlorophyll, K+ and K+/Na+ ratio. In the meantime, proline content, Cl- and Na+ accumulation in leaves were increased. It was also found that S. senegal and V. seyal tolerated high concentrations of NaCl (257 mM) and developed physiological and  molecular mechanisms, such as salt tolerance genes (NHX1), which allow them to be considered as moderated salt tolerant species and seemed to be potential species for the restoration of salt-affected land as P. juliflora.Key words: Multipurpose leguminous trees, abiotic stress, salt tolerance, Senegal

Response of Pearl Millet to nitrogen as affected by water deficit

In the Sahelian zone, low soil N could be as limiting as drought in pearl millet production. Although growth and crop productivity depend on several biochemical reactions in which the nitrogen metabolism plays a great role, there is little information available on how N uptake and key enzymes, nitrate reductase and glutamine synthetase, are affected by nitrogen and water interaction in millet. For this purpose, the millet variety cv. Souna III was grown in the field during the dry season under three levels of nitrogen fertilization (NO = 0.0, N1 = 17.13, and N2 = 68.50 kg N ha-1) and different water regimes (well-watered and water-stressed) in a split-plot experimental design. Irrigation was stopped for water-stressed plants during tillering, and the grain formation and filling phases, thereby giving rise to two water deficit cycles. A major quantity of mobilized N (79-100%) was taken up before flowering in all N treatments. Nitrogen uptake declined significantly only during the second water deficit cycle. During the first water deficit cycle, aboveground biomass was reduced and the maintenance of the N uptake resulted in increased N and nitrate concentrations. The water deficit reduced nitrate reductase activity jn all treatments and the effect was greater under high N. The increase in nitrate concentration under water deficit conditions showed that the reduction in nitrate reductase activity was probably not due to limiting nitrates. Glutamine synthetase activity was higher under the low N treatments, N1 and N0, showing the absence of a stimulating effect of glutamine synthetase activity by nitrate or ammonium. These results are discussed on the basis of their effect on grain N and grain yield.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Higher leaf nitrogen content is linked to tighter stomatalregulation of transpiration and more efficient water use acrossdryland trees

The least-cost economic theory of photosynthesis shows that water and nitrogen are mutu-ally substitutable resources to achieve a given carbon gain. However, vegetation in the Sahelhas to cope with the dual challenge imposed by drought and nutrient-poor soils.We addressed how variation in leaf nitrogen per area (Narea) modulates leaf oxygen andcarbon isotopic composition (δ18O,δ13C), as proxies of stomatal conductance and water-useefficiency, across 34 Sahelian woody species.Dryland species exhibited diverging leafδ18O andδ13C values, indicating large interspecificvariation in time-integrated stomatal conductance and water-use efficiency. Structural equa-tion modeling revealed that leaf Nareais a pivotal trait linked to multiple water-use traits. LeafNareawas positively linked to bothδ18O andδ13C, suggesting higher carboxylation capacityand tighter stomatal regulation of transpiration in N-rich species, which allows them toachieve higher water-use efficiency and more conservative water use.These adaptations represent a key physiological advantage of N-rich species, such aslegumes, that could contribute to their dominance across many dryland regions. This is thefirst report of a robust mechanistic link between leaf Nareaandδ18O in dryland vegetation that is consistent with core principles of plant physiology. δ13C, leafδ18O, plant isotopic composition,plant water-use strategies, Sahel, stomatalconductancepublishedVersio

Higher leaf nitrogen content is linked to tighter stomatalregulation of transpiration and more efficient water use acrossdryland trees

The least-cost economic theory of photosynthesis shows that water and nitrogen are mutu-ally substitutable resources to achieve a given carbon gain. However, vegetation in the Sahelhas to cope with the dual challenge imposed by drought and nutrient-poor soils.We addressed how variation in leaf nitrogen per area (Narea) modulates leaf oxygen andcarbon isotopic composition (δ18O,δ13C), as proxies of stomatal conductance and water-useefficiency, across 34 Sahelian woody species.Dryland species exhibited diverging leafδ18O andδ13C values, indicating large interspecificvariation in time-integrated stomatal conductance and water-use efficiency. Structural equa-tion modeling revealed that leaf Nareais a pivotal trait linked to multiple water-use traits. LeafNareawas positively linked to bothδ18O andδ13C, suggesting higher carboxylation capacityand tighter stomatal regulation of transpiration in N-rich species, which allows them toachieve higher water-use efficiency and more conservative water use.These adaptations represent a key physiological advantage of N-rich species, such aslegumes, that could contribute to their dominance across many dryland regions. This is thefirst report of a robust mechanistic link between leaf Nareaandδ18O in dryland vegetation that is consistent with core principles of plant physiology. δ13C, leafδ18O, plant isotopic composition,plant water-use strategies, Sahel, stomatalconductanc