Effect of Casuarina Plantations Inoculated with Arbuscular Mycorrhizal Fungi and Frankia on the Diversity of Herbaceous Vegetation in Saline Environments in Senegal

Land salinization is a major constraint for the practice of agriculture in the world. Considering the extent of this phenomenon, the rehabilitation of ecosystems degraded by salinization has become a priority to guarantee food security in semi-arid environments. The mechanical and chemical approaches for rehabilitating salt-affected soils being expensive, an alternative approach is to develop and utilize biological systems utilizing salt-tolerant plant species. Casuarina species are naturally halotolerant, but this tolerance has been shown to be improved when they are inoculated with arbuscular mycorrhizal fungi (AMF) and/or nitrogen-fixing bacteria (Frankia). Furthermore, Casuarina plantations have been proposed to promote the development of plant diversity. Thus, the aim of the current study was to evaluate the impact of a plantation comprising the species Casuarina inoculated with AMF and Frankia on the diversity of the sub-canopy and adjacent vegetation. Work was conducted on a plantation comprising Casurina equisetifolia and C. glauca variously inoculated with Frankia and Rhizophagus fasciculatus prior to field planting. The experimental area of 2500 m2 was divided into randomized blocks and vegetation sampling was conducted below and outside of the Casuarina canopy in 32 m2 plots. A total of 48 samples were taken annually over 3 years, with 24 taken from below the Casuarina canopy and 24 from outside the canopy. The results obtained show that co-inoculation with Frankia and Rhizophagus fasciculatus improves the height and survival rate of both species. After 4–5 years, there was greater species diversity and plant biomass in the sub-canopy environment compared with that of the adjacent environments. Our results suggest that inoculation of beneficial microbes can improve growth of Casuarina species and that planting of such species can improve the diversity of herbaceous vegetation in saline environments.