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.
Highlights
Current estimates project 40% of all plant species will become extinct within 30 years due to anthropogenic factors and climate change [1] and these dire projections have instilled a sense of urgency amongst conservationists to safeguard the species at highest risk
Depending on the species and where it grows, some terrestrial orchids may live for decades (e.g., Cypripedium calceolus), whereas others are ephemeral, quickly colonizing an area, setting seed, and perishing shortly thereafter within the span of one year (e.g., Habenaria repens [4])
Collecting orchid and soil samples from the Central Highlands of Madagascar for the current study was challenging due to problems with access, number of days required to screen and culture in vitro over a three-week period
Summary
Current estimates project 40% of all plant species will become extinct within 30 years due to anthropogenic factors and climate change [1] and these dire projections have instilled a sense of urgency amongst conservationists to safeguard the species at highest risk. Despite being incredibly diverse with upwards of 25,000 species worldwide [2], orchids are considered highly vulnerable to extinction. Union for Conservation of Nature (IUCN), half of all orchids that have already succumbed to extinction are herbaceous terrestrials despite comprising only about one-third of all species worldwide [3]. For conservationists faced with the burden of securing orchids under immediate threat, targeting the short-lived terrestrials is a logical priority. To date, those that have received the most study with respect to their biotic and abiotic requirements are rooted in temperate regions, and surprisingly little is known about their tropical counterparts.
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