Mycorrhizal specificity differences in epiphytic habitat: three epiphytic orchids harbor distinct ecological and physiological specificity.

Orchidaceae has diversified in tree canopies and accounts for 68% of vascular epiphytes. Differences in mycorrhizal communities among epiphytic orchids can reduce species competition for mycorrhizal fungi and contribute to niche partitioning, which may be a crucial driver of the unusual species diversification among orchids. Mycorrhizal specificity-the range of fungi allowing mycorrhizal partnerships-was evaluated by assessment of mycorrhizal communities in the field (ecological specificity) and symbiotic cultures in the laboratory (physiological specificity) for three epiphytic orchids inhabiting Japan. Mycorrhizal communities were assessed with co-existing individuals growing within 10 cm of each other, revealing that ecological specificity varied widely among the three species, ranging from dominance by a single Ceratobasidiaceae fungus to diverse mycobionts across the Ceratobasidiaceae and Tulasnellaceae. In vitro seed germination tests revealed clear differences in physiological specificity among the three orchids, and that the primary mycorrhizal partners contributed to seed germination. In vitro compatibility ranges of three orchids strongly reflect the mycorrhizal community composition of wild populations. This suggests that differences in in situ mycorrhizal communities are not strongly driven by environmental factors, but are primarily due to physiological differences among orchid species. This study shows that the symbiotic strategy among the epiphytic orchid species varies from specialized to generalized association, which may contribute to biotic niche partitioning.

The complete chloroplast genome sequence of Thrixspermum amplexicaule (Orchidaceae, Aeridinae).

The complete chloroplast genome sequence of Thrixspermum amplexicaule was assembled and analyzed in this work. The total chloroplast genome size of T. amplexicaule was 148,124 bp in length, containing a large single-copy (LSC) region of 86,079 bp, a small single-copy (SSC) region of 10,799 bp, and a pair of inverted repeat (IR) regions of 25,623 bp. The GC content of T. amplexicaule was 36.4%. It encoded a total of 120 unique genes, including 75 protein-coding genes, 37 tRNA genes, and eight rRNA genes. The results of phylogenetic analysis strongly supported that all four samples of Thrixspermum are monophyletic and T. amplexicaule was closely related to T. centipeda.

The complete plastid genome of Thrixspermum centipeda (Orchidaceae, Aeridinae).

The complete plastid genome of the type species of Thrixspermum, Th. centipeda, was determined and analyzed in this work. The plastome was 147,888 bp in length with 85,899 bp of the large single-copy (LSC) region, 11,055 bp of the small single-copy (SSC) region and 25,467 bp of the invert repeats (IR) regions. The genome contained 120 genes, including 74 protein-coding genes, 38 tRNA genes, and 8 rRNA genes. Phylogenetic analysis divided 18 Aeridinae plastomes into four groups, and Th. centipeda was sister to Th. tsii.

The complete plastid genome of Thrixspermum tsii (Orchidaceae, Aeridinae).

The complete plastid genome of Thrixspermum tsii was determined and analyzed in this work. The plastome was 149,689 bp in length with 86,778 bp of the large single-copy (LSC) region, 12,129 bp of the small single-copy (SSC) region and 25,391 bp of the inverted repeat (IR) regions. The genome contained 120 genes, 74 protein-coding genes, 38 tRNA genes, and 8 rRNA genes. Phylogenetic analysis of 17 Aeridinae plastomes suggested four groups were divided, and T. tsii was sister to T. japonicum.