Fungal diversity driven by bark features affects phorophyte preference in epiphytic orchids from southern China

Lorenzo Pecoraro,Xiao Wang,Hanne N Rasmussen,Finn N Rasmussen,Vincent S F T Merckx,Lei Cai,Sofia I F Gomes

doi:10.1038/s41598-021-90877-1

Lorenzo Pecoraro, Xiao Wang + Show 5 more

Open Access

https://doi.org/10.1038/s41598-021-90877-1

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Abstract

Epiphytic orchids exhibit varying degrees of phorophyte tree specificity. We performed a pilot study to investigate why epiphytic orchids prefer or avoid certain trees. We selected two orchid species, Panisea uniflora and Bulbophyllum odoratissimum co-occurring in a forest habitat in southern China, where they showed a specific association with Quercus yiwuensis and Pistacia weinmannifolia trees, respectively. We analysed a number of environmental factors potentially influencing the relationship between orchids and trees. Difference in bark features, such as water holding capacity and pH were recorded between Q. yiwuensis and P. weinmannifolia, which could influence both orchid seed germination and fungal diversity on the two phorophytes. Morphological and molecular culture-based methods, combined with metabarcoding analyses, were used to assess fungal communities associated with studied orchids and trees. A total of 162 fungal species in 74 genera were isolated from bark samples. Only two genera, Acremonium and Verticillium, were shared by the two phorophyte species. Metabarcoding analysis confirmed the presence of significantly different fungal communities on the investigated tree and orchid species, with considerable similarity between each orchid species and its host tree, suggesting that the orchid-host tree association is influenced by the fungal communities of the host tree bark.

Highlights

Epiphytic orchids exhibit varying degrees of phorophyte tree specificity
The highest fungal diversity was observed on neutral trees (N-trees, B. percoriacea) with 71 species in 49 genera (126 strains), followed by P. weinmannifolia (B-trees) with 47 (33 genera, 82 strains), and Q. yiwuensis (P-trees) with 31 (20 genera, 50 strains)
This study significantly contributed to our knowledge of different components of the complex habitat represented by trees that carry epiphytic orchids, and improved our understanding of some aspects of this phorophyteepiphyte relationship, which up to now, were nearly completely unknown[8,9]

Summary

Introduction

Epiphytic orchids exhibit varying degrees of phorophyte tree specificity. We performed a pilot study to investigate why epiphytic orchids prefer or avoid certain trees. Phorophyte bias could be related to the availability of mycorrhizal fungi that are essential for orchid seed germination and protocorm d evelopment[23,24,25] Both presence and performance of suitable mycobionts on the barks of different trees, which may be affected by a number of microenvironment physico-chemical factors, could determine orchid epiphyte distribution in n ature[9]. This question becomes more puzzling when the preferred trees differ among epiphytes that seem to mutually exclude each other, within the same area For this reason, we selected two orchid species, Panisea uniflora and Bulbophyllum odoratissimum co-occurring in a forest habitat in southern China. We analysed a number of biotic and abiotic environmental factors potentially influencing the relationship between the studied orchids and trees, including bark and orchid root fungal diversity. We hypothesised: (i) that the tree host specialization of the studied orchids was influenced by the presence of specific orchid mycorrhizal fungi, which were in turn biased toward particular tree species, and (ii) that the specific features of the bark either directly affected the early establishment of the orchid seedlings or did so indirectly through the fungal community that was able to grow on the bark

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