La grande muraille verte

National audienc

Climate change and desertification in Africa : The Great Green Wall

International audienc

Effets des principales essences de la grande muraille verte sénégalaise sur les taux d'azote minéral du sol et la biomasse microbienne

International audienceAn experiment was conducted over nine months in a field system in northern Senegal in order to determine the effects on soil nitrogen (N) cycling and the microbial biomass-C properties of five plant species proposed for the Senegalese Great Green Wall (GGW): Acacia senegal (L.) Willd., Acacia tortilis var. raddiana (Savi) Brenan, Balanites aegyptiaca (L.) Del., Boscia senegalensis (Pers.) Lam. ex Poir., and Sclerocarya birrea (A. Rich.) Hochst. Soil samples were collected to a depth of 0-10 cm, outside (control) and beneath tree canopies. Microbial biomass, inorganic N content and net mineralization of organic N were determined for the soil samples collected under trees, and compared to soils collected outside tree canopies. The results showed that concentrations of inorganic N and soil microbial biomass-C were generally higher under canopy cover and differed according to species. In May 2014 (end of the dry season), microbial biomass-C was higher under A. senegal (31.8 mg C/kg soil) and lower under B. senegalensis and in the control sample from outside the canopy (17 mg C/kg soil). A higher microbial biomass-C content was found under A. senegal (49 mg C/kg soil) and B. aegyptiaca (53.7 mg C/kg soil) in October 2014 (end of the rainy season) and in January 2015 (middle of the dry season). In May 2014, the concentration of ammonium was significantly higher under B. senegalensis (11.17 mu g/g soil), while the control sample (outside the canopy) had the lowest concentration (4.93 mu g/g soil). For nitrates, there was no significant difference between canopy species (P <= 0.05). These results can provide guidance for selecting tree species for the GGW according to their functioning and their effects on soil quality

Phenotypic and genotypic characterisation of root nodule bacteria nodulating Millettia pinnata (L.) Panigrahi, a biodiesel tree

Aims. Milletia pinnata is a leguminous tropical tree that produces seed oil suitable for biodiesel and is targeted to be planted on marginal land associated with nitrogen poor soil. This study aimed to identify effective rhizobia species for M. pinnata. Methods. Soil samples were collected from M. pinnata grown in Kununurra, Australia. Rhizobia were trapped, characterised and sequenced for 16S rRNA, atpD, dnaK and recA genes. Results. Forty isolates tolerated pH 7 – 9, temperatures 29 – 37 °C, salinity below 1 % NaCl, and had optimal growth on mannitol, arabinose or glutamate as a single carbon source, a few grew on sucrose and none grew on lactose. Inoculation of isolates increased shoot dry weight of M. pinnata’s seedlings in nitrogen minus media. Slow-growing isolates were closely related to Bradyrhizobium yuanmingense, Bradyrhizobium sp. DOA10, Bradyrhizobium sp. ORS305 and B. liaoningense LMG 18230T. The fast-growing isolates related to Rhizobium sp. 8211, R. miluonense CCBAU 41251T, R miluonense CC-B-L1, Rhizobium sp. CCBAU 51330 and Rhizobium sp. 43015. Conclusions. Millettia pinnata was effectively nodulated by slow-growing isolates related to Bradyrhizobium yuanmingense, Bradyrhizobium sp. DOA10 Bradyrhizobium sp. ORS305, B. liaoningense LMG 18230T and fast-growing isolates related Rhizobium sp. 8211, R. miluonense, Rhizobium sp. CCBAU 51330 and Rhizobium sp. 43015