Arbuscular mycorrhizal fungi (AMF) typically exhibit reduced diversity in nutrient-rich soils. However, whether the influence of host plants on AMF within the rhizosphere is direct or indirect through the alteration of soil nutrient levels has yet to be determined. This study explored the diversity and colonization of AMF in the National Tropical Fruit Tree Genebank, where chemical fertilizers are used to preserve minor tropical fruit germplasms. We aimed to understand the direct and indirect effects of host plants on AMF community dynamics, sporulation, and colonization. By analyzing fine roots and rhizosphere soil from 12 tropical fruit trees, we assessed mycorrhizal colonization indices, soil nutrients, AMF spore density, and community structure. Despite their low colonization density and arbuscular abundance, all the tree roots harbored AMF, with spore densities ranging from 24.00 to 204.80 spores/100 g of dry soil. High-throughput sequencing identified 207 AMF virtual taxa (VTs) from 60 soil samples, with dominant taxa, including early-evolved Paraglomus fungi and ruderal AMF, being minimally affected by soil nutrient levels. Interestingly, there was no correlation between α diversity and spore density. Structural equation modeling (SEM) indicated that host plant evolutionary divergence time (ET) directly influenced AMF α diversity indices and indirectly impacted spore density via soil nutrients. However, neither ETs nor soil nutrients significantly affected the AMF community structure, with only arbuscular abundance showing a negative correlation with ET. This research underscores the intricate relationship between host plants and AMF in genebanks, offering insights for effective AMF resource management and informed conservation practices. Graphical Abstract

The regulatory network governing triacylglycerol (TAG) and fatty acid (FA) accumulation in hexaploid Camellia oleifera kernels remains unclear due to the lack of an appropriate reference genome. In this study, we combined oil trait measurements with multi-omics analyses (global transcriptomics, miRNA sequencing, proteomics, and metabolomics) across 3 harvest stages, using the hexaploid C. oleifera ‘Changlin 40’ genome as reference. Integrated analysis of oil traits and multi-omics data demonstrated that premature harvesting (1 week before the recommended date) decreased oil production and enhanced saturated FAs composition, while postponed harvesting (1 week after the recommended date) preserved oil yield and increased oleic and linolenic acid contents. Comprehensive pathway analysis identified 11 key metabolic pathways involved in TAG and FA biosynthesis and catabolism, revealing their coordination with terpene and flavonoid synthesis under the influence of carbohydrate metabolism. Within the 11 metabolic pathways, key regulatory enzymes comprised alcohol dehydrogenase and galactosidase that negatively regulated TAG biosynthesis, palmitoyl-protein thioesterase that mediated short-chain saturated FA formation, and acyl-CoA thioesterase that enhanced long-chain unsaturated FA production. Additionally, we detected novel associations between TAG/FA accumulation and non-canonical factors, including noncoding RNAs (circR007, lncR114741, miR167h, miR166, miR398a-3p, miR398d, and miR396a-3p), proteins (seed storage protein, caffeic acid O-methyltransferase, galactose oxidase, No Pollen Germination 1, Coronatine Insensitive 1), and metabolites (L-carnitine and L-glutamate). The reliability of our findings was confirmed through qRT-PCR (RNA validation) and Parallel Reaction Monitoring (protein validation). This study established the regulatory network TAG and FA accumulation in hexaploid C. oleifera kernels, and provided foundational molecular framework for breeding high-yield, high-quality C. oleifera cultivars through marker-assisted selection.