Occurrence of Nodulation in Unexplored Leguminous Trees Native to the West African Tropical Rainforest and Inoculation Response of Native Species useful in Reforestation

Background

Few studies examine the ability of leguminous tree species to nodulate and fix atmospheric N, especially symbiotically with rhizobia; this study seeks to fill that research gap.  The occurrence of nodulation was determined in 156 mature leguminous species growing in 6 natural forest areas in south-eastern Guinea and an in situ experiment of rhizobia inoculation was performed on 8 selected tree species.

Research Goals & Methods

Field observations were carried without any sampling protocol, and roots of targeted species were systematically observed for nodulation when encountered. In situ nodules were collected from mature A. adianthifolia, A. ferruginea, A. zygia, E. guineensis, M. rhodantha and M. zechiana growing in the natural forests and inoculated, nursed and transplanted to the field close to the nursery. 4 months of nursery treatment followed by 11 months after transplantation of plants to the field.

Conclusions & Takeaways

Results show a highly significant and positive effect of inoculation with Bradyrhizobium sp. strains on both stem height and diameter growth of the eight tree species tested. Height differences were enhanced in the following species A. zygia, A. ferruginea, E. guineensis, and M. rhodantha. But there was an important decline of the inoculation effect in A. adianthifolia although it remained positive.  There a need to identify the nodulation status of unexplored local trees before inoculating them with rhizobia in the context of plantation projects or reforestation programs in degraded humid tropical forests.