Rhizosphere fungi promote a critically endangered living-fossil species, but are inadequate for preventing its extinction

Hua Xing, School of Ecological and Environmental Sciences, East China Normal University, Shanghai, China, Yu Liu Sr. and Fang L. He Sr., School of Ecology and Environmental Sciences, East China Normal University, Shanghai, China, Fang L. He Sr., Department of Renewable Resources, University of Alberta, Edmonton, AB, Canada

Background/Question/Methods
How a large fraction of terrestrial plant species persist has puzzled ecologists as far back as the middle of the last century. Understanding the mechanisms underlying the rarity of species represents a critical knowledge gap for understanding the “commonness of rarity” pattern and for conservation of biodiversity. Although many hypotheses have been proposed to explain why species rarity is so widespread, and the importance of symbiosis between soil fungi and host plants to the welfare of hosts has long been recognized, the role of these symbioses in maintaining the rarity of host plants is not understood.
Here, we investigated the possible role of rhizosphere fungi in contributing to its rarity. Specifically, we focused on the following three questions: (i) whether there was a unique rhizosphere fungal community associated with A. beshanzuensis that was distinctive from other co-occurring tree species, and whether such a community could possibly impede this species from colonizing new sites, (ii) whether a high load of ectomycorrhizal fungi, but a low load of plant-pathogenic fungi in A. beshanzuensis rhizospheres were present relative to its congeners, with the hypothesis that A. beshanzuensis could achieve greater benefits from beneficial rhizosphere fungi that could underlie the persistence of the endangered tree species, and (iii) whether A. beshanzuensis seedlings performed better in native soils, thereby empirically affirming the prediction of the second question.
Results/Conclusions
We found that rhizosphere fungal composition of A. beshanzuensis was very different from that of other congeneric Abies species. High loads of mutualistic fungi and low loads of pathogenic fungi in A. beshanzuensis rhizospheres suggest that this species might achieve growth advantages via rhizosphere fungi to promote its regeneration. This prediction was confirmed by A. beshanzuensis seedling performance experiment in a shade house. Despite the beneficial effect of the unique rhizosphere fungi, it seems A. beshanzuensis was not able to escape the curse of extinction vortex. Our study highlights that stabilizing mechanisms alone are not sufficient for preventing species extinction.