Dual gradient dynamics: morpho-anatomical and symbiotic fungal communities in Fraxinus Mandshurica fine roots across root order and habitats.

backgroundThe cooperation between fine roots and mycorrhizal fungi is of great significance in terms of adapting to harsh environments and acquiring resources. Nevertheless, how this cooperative relationship responds in different environments remains unclear. To understand the mechanisms of the interaction between root order structure and morphology and endophytic fungi in different habitats, we investigated the anatomical and chemical traits of first five order roots, as well as the percentage of mycorrhizal colonization and the community structure of root-inhabiting fungi of Fraxinus mandshurica in the semi-arid and humid habitats of Northeast China.

resultsIn contrast to humid habitats, the fine roots of F. mandshurica in semi-arid habitats exhibited more conservative resource-acquisition traits, characterized by greater root diameter and tissue density alongside reduced specific root length, specific root surface area and nitrogen and phosphorus concentrations. Concurrently, anatomical traits showed adaptations for symbiotic fungi association: cortical cell thickness, cell size and the ratio of cortical thickness to half of the stele diameter were higher in absorptive roots. The diversity of symbiotic fungi, represented by arbuscular mycorrhizal fungi (AMF), and the percentage of mycorrhizal colonization were significantly higher than those in humid habitats, enhancing resource acquisition. It is worth noting that in semi-arid habitats, not only do the absorptive roots of F. mandshurica habour a higher proportion of AMF, but AMF hyphae and vesicles were also observed in the transport roots. Moreover, AMF extending from absorptive roots to transport roots was detected, representing a novel resource-acquisition strategy.

conclusionsThe semi-arid habitat promotes the development of conservative resource-acquisition traits in the fine roots of F. mandshurica and expands the spatial extent of root nutrient exchange. It also enhances the ability of fine roots to recruit symbiotic fungi and facilitates the extension of mycorrhizal fungal hyphae from absorptive roots to transport roots, thereby strengthening the response of roots and mycorrhizal fungi to adverse conditions.