Unique mycorrhizal association is a conservation dilemma for the threatened tree species

Abstract

Tree health is fundamental to maintaining forest structure and ecosystem functioning. Among the many factors influencing tree growth and survival, ectomycorrhizal (ECM) fungi are essential symbionts that provide nutrients to their host trees and enhance resistance to environmental stress and pathogens. However, studies on the symbiotic relationships between threatened tree species and ECM fungi remain limited. In this study, we investigated the key symbiotic fungi associated with the IUCN Vulnerable Taiwan spruce (Picea morrisonicola), while simultaneously examining the diversity of ECM fungi associated with neighboring Taiwan hemlock (Tsuga chinensis var. formosana) and Taiwan fir (Abies kawakamii) forests. Roots and forest soils were collected from these three endemic Pinaceae species across ten high-elevation forests in the three major mountain ranges of Taiwan, and their ECM fungal communities were analyzed using high-throughput sequencing. The results showed that the ECM fungal communities associated with the roots and forest soils of Taiwan spruce were significantly different from those of Taiwan hemlock and Taiwan fir. The dominant symbiotic fungi associated with Taiwan spruce were extremely rare in the other two Pinaceae forests. The absence of compatible symbiotic fungi may limit the dispersal and population expansion of Taiwan spruce. Our findings highlight the importance of in situ conservation of Taiwan spruce, which protects not only the threatened tree species itself but also its unique ECM fungal reservoir. The key symbiotic fungal taxa and their spatial distributions should be taken into consideration when developing ex situ conservation and transplantation strategies for Taiwan spruce.

Methodology and Implementation Steps

This study used molecular approaches to investigate the diversity and distribution of ectomycorrhizal (ECM) fungi associated with the roots and forest soils of three high-elevation endemic Pinaceae tree species in Taiwan: Taiwan spruce (Picea morrisonicola), Taiwan hemlock (Tsuga chinensis var. formosana), and Taiwan fir (Abies kawakamii). A total of ten forest sites were established across the Xue, Central, and Jade Mountain Ranges of Taiwan. Field sampling was conducted from August 2020 to April 2021. At each site, three healthy individuals at least 10 m apart were randomly selected to ensure sample independence. Total DNA were extracted from the collected root and soil samples. Target fungal sequences were amplified using universal fungal primers and sequenced on the Illumina MiSeq platform. The resulting sequence data were used to compare the diversity and community composition of ectomycorrhizal fungi among the three tree species. This study further evaluated the potential impacts of climate change on the diversity of symbiotic fungi associated with threatened tree species, providing a scientific basis for the conservation and restoration of high-mountain forests.

Innovation and Cross-Disciplinary Collaboration

Conservation studies of threatened tree species have focused on population genetic diversity, habitat suitability based on climatic conditions and topography, and predictions of potential species distributions, while the influence of plant–soil microbial symbioses has received relatively little attention. This study is highly original in the fields of forest ecology and biodiversity conservation, representing the first study worldwide to reveal the ectomycorrhizal fungal community associated with a threatened spruce species.

Expected Results and Contributions

This study established a comprehensive dataset on the diversity and ecology of ectomycorrhizal fungi in Taiwan's high-mountain forests. The resulting data have been deposited in the Taiwan Biodiversity Information Facility (TaiBIF) and global biodiversity databases to support the conservation of Taiwan spruce, the development of conservation strategies for other threatened tree species, and future assessments of climate change impacts. Our results demonstrate that the Vulnerable Taiwan spruce harbors a highly specialized ectomycorrhizal fungal community, with its dominant symbiotic fungi being rare in neighboring Taiwan hemlock and Taiwan fir forests (Figure 2). These findings suggest that the availability of compatible symbiotic fungi may be an important factor limiting the population expansion and dispersal of Taiwan spruce.