Unique ectomycorrhizal fungal association is a major conservation dilemma for the threatened ectomycorrhizal tree species

Ectomycorrhizal (ECM) fungi play a critical role in supporting tree growth, health and survival. However, ECM symbioses in threatened trees have rarely been explored as a missing link in tree conservation. In this study, we identified the key ECM fungal partners of the vulnerable Taiwan spruce (Picea morrisonicola) and examined their distribution in nearby dominant tree species, Taiwan hemlock (Tsuga chinensis var. formosana) and Taiwan fir (Abies kawakamii), using Illumina MiSeq sequencing. A total of 33 root samples and 29 bulk soil samples were analyzed from ten forests across three major mountain ranges in Taiwan. Results showed that ECM fungal communities in roots and bulk soil of Taiwan spruce were distinct from those of Taiwan hemlock and Taiwan fir, and their dominant ECM fungal partners were rarely found in the other two Pinaceae forests. In particular, the /amphinema-tylospora lineage, which is known to form specific symbioses with spruce species, was highly abundant in Taiwan spruce roots (20.8 % relative abundance) and soils (17.4 %) but entirely absent from Taiwan hemlock and Taiwan fir forests. This suggests that the absence of compatible ECM fungi may restrict the natural migration and range expansion of Taiwan spruce, posing a challenge to its survival under climate change. For the effective conservation of threatened ECM-dependent trees, it is essential to understand their key fungal partners and their distribution, to identify potential in-situ conservation sites or translocation sites. Long-term monitoring may help to track changes in adaptation and resilience of both trees and ECM fungi under climate change.