Nicolas Niemenak

University of Yaounde I, Cameroon

Abstract Title:

Environmental and host-driven shaping of arbuscular mycorrhizal fungal communities in cacao (Theobroma cacao) agroforestry systems across agro-ecological zones in cameroon

Research Interests:

Climate change is intensifying environmental constraints on tropical agroecosystems. Despite the central role of soil microbiomes in ecosystem resilience, the dynamics of arbuscular mycorrhizal fungi (AMF) in cacao-based agroforestry systems, a key cash crop in the country, remain poorly understood. This study aimed to assess the community structure, diversity, and environmental drivers of AMF associated with cacao tree in soils across three agro-ecological zones of Cameroon. Soil samples were collected from nine localities and subjected to physicochemical analyses, including pH, organic carbon, total nitrogen, and C/N ratio. AMF communities were characterized using an integrative approach combining morphological identification and Illumina sequencing targeting the 18S rRNA gene for native soil. Community shifts following trapping were assessed in both soil and root compartments. Taxonomic assignments were performed using the MaarjAM database and SILVA database. Results showed that soil properties significantly varied across agro-ecological zones and with altitude influenced AMF community structure. Bioinformatic analyses revealed discrepancies between reference databases, with the SILVA database showing greater consistency with morphological identification. Native soils were dominated by Glomeraceae (57.7%), with higher species richness observed in the Western Highlands compared to monomodal rainfall zones, while bimodal zones displayed intermediate richness with high variability. 22.36% of OTUs were unresolved or ambiguously assigned using SILVA highlighting a critical issue: environmental DNA sequences, particularly those from African ecosystems, remain underrepresented in current taxonomic databases. Trapping cultures induced substantial shifts in AMF community composition, particularly under sorghum cultivation, which promoted previously undetected families such as Paraglomeraceae, Archaeosporaceae, and Ambisporaceae. Overall, this study demonstrates that AMF community structure in cacao systems is shaped by both environmental gradients and host plant effects. It also underscores the importance of database selection in microbial ecology studies and provides new insights for the management of soil microbiomes to enhance agroecosystem resilience under ongoing Climate Change.