Effect of mycorrhizae on aboveground biomass in monodominant Gilbertiodendron dewevrei and mixed species forests in a tropical rainforests of the Congo Basin

The mechanisms underlying the relationship between aboveground biomass and mycorrhizal intensity are poorly documented in tropical forests. This study assesses the influence of mycorrhizae on aboveground biomass (AGB) in two adjacent mixed species forests stands and monodominant Gilbertiodendron dewevrei stands in the Dja Biosphere Reserve. The methodology used included inventories of trees ≥ 10 cm in diameter, sampling of rootlets with diameter < 2 mm from the collar to the most branched level in one ha permanent plots and assessment of mycorrhizal structures in one cm rootlets at a rate of 30 rootlets/tree. The study observed 26 100 rootlets originating from 290 trees belonging to 115 species, 96 genera and 35 families in themixed species stands while 5490 rootlets were observed in the monodominant G. dewevrei stands comprising 61 trees, 34 species, 29 genera and 18 families. Within the mixed species stands, 77.39% of the species are associated with endomycorrhizae while only 22.61% of the species did not form mychorrhizae association. For the G. dewevrei stands 70.59% formed endomycorrhizae while 26.47% of species have no mychorrhizae. Ectomycorrhiza was recorded for only 2.94% of the species in the G. dewevrei stands. Variation in tree diameter did not dependent on mycorrhizal intensity. Wilcoxon test showed that the AGB in the mixed forests is statistically lower than that in the monodominant forest (p-value =0.03). G. dewevrei stands should be considered separately from mixed species stands when calculating AGB. A better understanding of mycorrhizae symbiosis will clarify their contributions to tropical forest functioning.