Orchids account for about 10 percent of all plant species on earth, making them the biggest plant family. But many orchids are threatened and endangered due to habitat loss. In a paper published in the journal Molecular Ecology, Smithsonian ecologists revealed that an orchid's fate hinges on two factors: a forest's age and its fungi.
Orchids depend entirely on microscopic fungi in the early stages of their lives. Without the nutrients orchids get by digesting these host fungi, their seeds often will not germinate. While the orchid-fungi's relationship is known to researchers, very little is known about what the fungi need to survive. Led by Melissa McCormick, Smithsonian researchers set up a study four years ago to find out what helps the fungi thrive and how that would impact the orchids.
The researchers focused on three endangered species in the United States of America. After planting orchid seeds in dozens of experimental plots, they also added particular host fungi needed by each orchid to half the plots. Then they followed the fate of the orchids and fungi in six study sites: three in younger forests (50 to 70 years old) and three in older forests (120 to 150 years old). They found the orchid seeds germinated only where the fungi they needed where abundant, not merely present.
The fungi showed a strong preference for older forests.
Soil samples taken from older forest plots had host fungi that were five to 12 times more abundant compared to younger forests, even where the research team had not added them - and they were more diverse. More mature plots averaged 3.6 different Tulasnella fungi species per soil sample (a group of fungi beneficial to these orchids), while the younger ones averaged only 1.3 Host fungi were also more abundant in plots where rotting wood was added. These host fungi, which are primarily decomposers, may grow better in places where decomposing wood or leaves are plentiful.
All this implies that to save endangered orchids, planting new forests may not be enough. If the forests are not old enough or do not have enough of the right fungi, lost orchids may take decades to return, if they return at all.