Fungal Diversity of Selected Habitat Specific Cynorkis Species (Orchidaceae) in the Central Highlands of Madagascar

Abstract

About 90% of Cynorkis species are endemic to the biodiversity hotspot of Madagascar. This terrestrial habitat-specific genus received little study for fungal diversity to support conservation. We evaluated the diversity of culturable fungi of 11 species and soil characteristics from six sites spanning a >40 km radius in and along the region’s inselbergs. Peloton-forming fungi were grown in vitro from root/protocorm slices and positively identified using DNA sequencing. The fungal diversity was then correlated with soil pH, NO3-N, P, and K. All species harbored either putative mycorrhizal associates in the Rhizoctonia complex or Hypocreales fungi. Tulasnella Operational Taxonomic Units (OTUs) were most prevalent in all soil types while Serendipita OTUs were found in species inhabiting granite/rock outcrops in moist soil (seepage areas). Most Cynorkis species were present in soil with low NO3-N and P levels with diversity of mycorrhizal fungi inversely correlated to NO3-N levels. Of the different orchid life stages sampled, only one species (Cynorkis fastigiata) yielded putative mycorrhizal fungi from juvenile stages. As diversity of mycorrhizal fungi of Cynorkis spp. was negatively correlated with NO3-N, and majority of the studied taxa were found in soils with low NO3-N and P contents, reintroduction studies must include analysis of N and P in detail. For the first time, we showed that the assemblage of culturable fungi in the roots of habitat-specific species of Cynorkis (Orchidaceae) are intimately tied to specific soil characteristics.

Preventing Extinction of the Critically Endangered Dactylorhiza incarnata subsp. ochroleuca in Britain Using Symbiotic Seedlings for Reintroduction

“…As this site is hosting a diverse range of orchids seed-germination-compatible Tulasnella OTU from southern marsh orchid (from a chalky wet habitat) was tested among many other isolates of putative mycorrhizal fungi for yellow early marsh. The lineage of Tulasnellaceae, a common mycorrhizal fungus in orchids shows generalist behavior as reported in many Dactylorhiza and other terrestrial orchids [ 28 , 29 , 30 , 31 , 32 ].…”

“…In three terrestrial orchids, it is demonstrated that one Tulasnella strain exhibited high compatibility across the three distantly related host species showing the generalist nature of this lineage of mycorrhizal fungus [ 29 ]. Studies in several species of the terrestrial genus of Cynorkis from Madagascar and found that most of those species recruited fungi of Tulasnella lineage at various growth phases and under different soil conditions [ 31 ]. In the current study the donor orchid, D. praetermissa was from a moist chalky site while the recipient orchid was from a chalky fen habitat.…”

“…The result of this study shows the only remaining population is in a nutrient-rich habitat compared to several other reports where orchids are found in nutrient-poor habitats. In Cephalanthera rubra [ 4 ] and Cynorkis [ 31 ] it is found that elevated P content leads to lower mycorrhizal diversity. Differences in mycorrhizal diversity among sites were driven by differences in soil P and N content [ 34 ], the authors argue that higher soil nutrient availability promotes specialization in orchid–mycorrhizal associations for soils with high N availability.…”

“…The current study used fungi available from plants at different growth phases and found that Tulsanella OTU from mature phase D. praetermissa was a germination-compatible fungus. This has been proved as a successful approach in identifying putative mycorrhizal fungi in orchids from Madagascar [ 17 , 24 , 31 , 32 , 39 ]. Putative mycorrhizal fungus isolate from seedlings was more efficient at supporting seed germination compared to those isolated from adult roots in Dendrobium exile [ 38 , 40 ] suggested that the fungi used in conservation must be limited to mycorrhizal fungi acquired from the same or nearby populations.…”

Dominant Dendrobium officinale mycorrhizal partners vary among habitats and strongly induce seed germination in vitro

“…Among lithophytic and epiphytic individuals of Coelogyne corymbosa, Serendipitaceae fungi contributed a relatively large portion of the OTU communities specific to lithophytic orchids (Qin et al, 2020). Yokoya et al (2021) surveyed 11 growing Cynorkis orchid species within lithophytic and terrestrial habitats and found that Serendipitaceae OTUs were frequently found in species inhabiting granite/rock, whereas Tulasnellaceae OTUs were found in both habitat types; they also reported that most Serendipitaceae OTUs were found in the habitat with higher phosphorus and nitrogen content, which may indicate that Serendipitaceae prefers soil conditions with high phosphorus and nitrogen levels. These differences in nutrient conditions may contribute to OMF community differences between lithophytic and epiphytic individuals in D. officinale.…”