Changes in Intraspecific Diversity of the Arbuscular Mycorrhizal Community Involved in Plant-Plant Interactions Between Sporobolus robustus Kunth and Prosopis juliflora (Swartz) DC Along an Environmental Gradient.

The intensification of biological processes coping with salt stress became a major issue to mitigate land degradation. The Sine-Saloum Delta in Senegal is characterized by salt-affected soils with vegetation dominated by salt-tolerant grass Sporobolus robustus and shrubs like Prosopis juliflora. Plant experiments in controlled conditions suggested that arbuscular mycorrhizal (AM) fungi might be the key actors of facilitation process observed between S. robustus and P. juliflora, but the AM fungal community determinants are largely unknown. The current field-based study aimed at (1) characterizing the environmental drivers (rhizosphere physico-chemical properties, plant type and season) of the AM fungal community along an environmental gradient and (2) identifying the AM fungal taxa that might explain the S. robustus-mediated benefits to P. juliflora. Glomeraceae predominated in the two plants, but a higher richness was observed for S. robustus. The pH and salinity were the main drivers of AM fungal community associated with the two plants, negatively impacting richness and diversity. However, while a negative impact was also observed on mycorrhizal colonization for S. robustus, P. juliflora showed opposite colonization patterns. Furthermore, no change was observed in terms of AM fungal community dissimilarity between the two plants along the environmental gradient as would be expected according to the stress-gradient and complementary hypotheses when a facilitation process occurs. However, changes in intraspecific diversity of shared AM fungal community between the two plants were observed, highlighting 23 AM fungal OTUs associated with both plants and the highest salinity levels. Consequently, the increase of their abundance and frequency along the environmental gradient might suggest their potential role in the facilitation process that can take place between the two plants. Their use in ecological engineering could also represent promising avenues for improving vegetation restoration in saline Senegalese's lands.

Correction to: Tracing Rhizophagus irregularis isolate IR27 in Ziziphus mauritiana roots under field conditions.

The authors of the above-mentioned published article inadvertently omitted Dirk Redecker, Dioumacor Fall and Diaminatou Sanogo from the list of authors. The names and their affiliations presented in this paper.

The rhizosphere of the halophytic grass Sporobolus robustus Kunth hosts rhizobium genospecies that are efficient on Prosopis juliflora (Sw.) DC and Vachellia seyal (Del.) P.J.H. Hurter seedlings.

The aim of this study was to survey the abundance and genetic diversity of legume-nodulating rhizobia (LNR) in the rhizosphere of a salt-tolerant grass, Sporobolus robustus Kunth, in the dry and rainy seasons along a salinity gradient, and to test their effectiveness on Prosopis juliflora (SW.) DC and Vachellia seyal (Del.) P.J.H. Hurter seedlings. The results showed a significant decrease in LNR population density and diversity in response to salinity, particularly during the dry season. A phylogenetic analysis of the 16S-23S rRNA ITS region clustered the 232 rhizobium isolates into three genera and 12 distinct representative genotypes: Mesorhizobium (8 genotypes), Ensifer (2 genotypes) and Rhizobium (2 genotypes). Of these genotypes, 2 were only found in the dry season, 4 exclusively in the rainy season and 6 were found in both seasons. Isolates of the Mesorhizobium and Ensifer genera were more abundant than those of Rhizobium, with 55%, 44% and 1% of the total strains, respectively. The abundance of the Mesorhizobium isolates appeared to increase in the dry season, suggesting that they were more adapted to environmental aridity than Ensifer genospecies. Conversely, Ensifer genospecies were more tolerant of high salinity levels than the other genospecies. However, Ensifer genospeciesproved to be the most efficient strains on P. juliflora and V. seyal seedlings. We concluded that S. robustus hosts efficient rhizobium strains in its rhizosphere, suggesting its ability to act as a nurse plant to facilitate seedling recruitment of P. juliflora and V. seyal in saline soils.

Tracing Rhizophagus irregularis isolate IR27 in Ziziphus mauritiana roots under field conditions.

Arbuscular mycorrhizal fungi (AMF) play a major role as biofertilizer for sustainable agriculture. Nevertheless, it is still poorly documented whether inoculated AMF can successfully establish in field soils as exotic AMF and improve plant growth and productivity. Further, the fate of an exogenous inoculum is still poorly understood. Here, we pre-inoculated two cultivars (Tasset and Gola) of the fruit tree Ziziphus mauritiana (jujube) with the exotic AM fungus Rhizophagus irregularis isolate IR27 before transplantation in the field. In two experiments, tracking and quantification of R. irregularis IR27 were assessed in a 13-month-old jujube and an 18-month-old jujube in two fields located in Senegal. Our results showed that the inoculant R. irregularis IR27 was quantitatively traced and discriminated from native R. irregularis isolates in roots by using a qPCR assay targeting a fragment of the RNA polymerase II gene (RPB1), and that the inoculum represented only fractions ranging from 11 to 15% of the Rhizophagus genus in the two plantations 13 and 18 months after transplantation, respectively. This study validates the use of the RPB1 gene as marker for a relative quantification of a mycorrhizal inoculant fungus isolate in the field.