Can mushrooms save this endangered Hawaiian tree?

Nicole Hynson is usually brought in to help when all else fails. A University of Hawaii conservation biologist works to bring all kinds of critically endangered plants back from the brink of extinction. Unfortunately, she’s busy in her home state of Hawaii, also known as the extinction capital of the world. Her latest conservation target is a flowering tree that is fighting a losing battle in the wild: Gardenia brighamii, or, as it is known in some local communities, na’u.

Na’u is one of three species of gardenia endemic to the archipelago. Historical records indicate that Native Hawaiians made tools from na’u wood and harvested its fruit for dye. The crowning glory of na’u is his glory fragrant flowera pearl flower that was once often woven into traditional flower wreaths called leis. But now the wood, fruit and flowers of this tree are too rare for commercial or occasional use. Due to drought, agriculture, competition with invasive plants and fires, this species, which was once found throughout Hawaii, is now found on one island – Lanai. There are about ten known individuals living there in the wild, making na’ one of the rarest plants in the world.

“These gardenias are absolutely beautiful, wonderful plants with deep cultural history and value,” says Mike Opgenorth, director of the National Tropical Botanical Garden and a former student of Hynson’s who worked on G. brighamii security. Like other local flora, they play a key role in indigenous traditional knowledge. “When you lose some of these plants, you lose some of the Hawaiian culture.”

To grow robust seedlings that can strengthen the species in the wild, Hynson’s team is turning to a new tool in the plant protection arsenal: mycorrhizal fungi. The community of beneficial microorganisms inhabiting plant roots is the botanical equivalent of: intestinal microbiome. In exchange for food, they act as mycorrhizal fungi all kinds of functions for the host plant – they provide the plant with mineral nutrients from the soil, act as extensions of the roots, helping the plant absorb more water and increase the host’s resistance to pathogens. In return, they obtain energy-rich sugars and lipids from photosynthesizing plants. Plant-fungus interactions are rich symbiotic pacts that are retrograde in nature to the time when plants first colonized land about 500 million years ago.

Despite their countless and long-lasting contributions to plants throughout evolutionary history, mycorrhizal fungi have been largely neglected by agronomists and botanists until recently. To grow healthy plants, conventional gardening relied on the intensive use of chemicals such as fungicides to prevent all kinds of diseases. However, this practice meant that fortifying mushrooms and the nutritional benefits they provide were excluded from shaping plant health. Mycorrhiza exposure in na’ restoration takes this extreme approach a step further and promotes growing conditions that more closely resemble the plant’s natural environment.

The use of nature’s agents

For over 20 years, nature conservationists have been “taking care of” G. brighamii seedlings in greenhouses, growing them in sterile conditions and sprinkling them with fertilizers and pesticides. In this resource-intensive approach, survival rates have become re-wild G. brighamii According to a report by Hynson, the figure is less than 10 percent. Out in the open, pampered seedlings weaken as they encounter the full brunt of the elements and other natural hazards. Often, these people must rely on synthetic chemicals for the rest of their lives, Hynson says.

Hynson’s strategy is to completely replace artificial chemicals with probiotics from mycorrhizal fungi that plants would normally produce in nature over time. In theory, these living root-based defenses should help the plant live more independently.

Lena Neuenkamp, ​​a plant and mycorrhizal ecologist at Germany’s University of Münster who was not involved in the project, says it’s a bit like what’s done before captive zoo animals are rewilded. He says you want to give them the best possible start in life, such as a healthy internal microbiome, so they have the best chance of surviving on their own when they return to their natural environment.

“Native mycorrhizal contact can be really important for high conservation value plants and their establishment,” says Jim Bever, a plant ecologist at the University of Kansas who was not involved in the project. He used mycorrhizal inoculations to recreate prairie grasses in the American heartland. “Our experience in the Midwest is very consistent with Nicole’s goal.”

Hynson’s group collects soil samples from the wild G. brighamii people to pick friendly mushrooms. “It’s quite a journey to bring back some of these samples,” he says, considering there are so many of them G. brighamii trees live in remote locations. Back in the greenhouse, Hynson cultivates the microbes present in the fictional grass host. After several months of increasing the number of mushrooms, researchers collect spores and spray them G. brighamii seedlings in the laboratory.

So far, the results are promising. The team observed that the vaccinated seedlings grew three times faster than the uninitiated seedlings. It will be at least another six months before the seedlings are ready for the final test: transplanting into outdoor restoration sites.

Of course, rapid growth in a greenhouse does not necessarily guarantee survival in the wild. But given the challenges of breeding G. brighamii in captivity Hynson considers early success with reinforced seedlings a victory. “I expect them to continue on this positive trajectory,” Hyson says. “It’s not always clear whether they will survive; All we can do is try to make them as strong as possible.”

Given that the mycorrhizal method does not use any fertilizers or pesticides, this practice may be more sustainable in the long run. “If we can generate plants that perform well without all this input, that means savings on all fronts,” Hynson says.

Race against time

The challenge in working with mycorrhizal fungi is that plants and fungi are extremely picky about who they partner with. For this reason, store-bought generic mycorrhizal mix for houseplants often does not provide the expected benefits. Mixtures usually contain a fertilizer that is intended to induce certain growth effects, which can mislead plant parents into thinking that the inoculation is working when in fact the fertilizer is doing its job.

Which fungal helpers a plant allows into its circle is complex — a healthy mycorrhizal crew for a single plant can number as many as 80 members, Hynson says.

Neuenkamp says it’s not difficult to find species of mycorrhizal fungi because they are found everywhere. But the trick to building a dream team is to find those who make a positive difference.

For now, Hynson’s team is obtaining small relics of wild gardenia for entire microbial communities. Scientists test soil samples from across the state – taken from healthy, flailing and even dead plants – and grow hundreds of seedlings to select the best mycorrhizal mix. “The idea is that if we split our collection between a few different trees, hopefully we can hit a pot of gold,” Hynson says.

Scientists cannot say which soil sample will give the best results. However, once the results are back, they plan to conduct DNA fingerprinting on the most effective soil sample to determine which fungi are present and what services they provide to the host. This will help scientists reproducibly determine the optimal mycorrhizal inoculation formula for all future na’u crops.

The entire conservation process is slow, and researchers are well aware that they are racing against time. In the three years since Hynson began her efforts to save the species, she has seen wild specimens die off faster than she has been able to breed greenhouse varieties to adulthood.

Last year, she and a team of other botanists traveled to Oahu to check on the last remaining na’u tree. However, their grueling three-hour journey, pounding the hills in the rain, ended in disappointment. Where Oahu’s last tree once stood, all that remained was the skeleton of a fallen tree with a split trunk and bare branches. It has succumbed to the combined threats of competition from exotic fauna and habitat changes caused by climate change. “We all just enjoyed the moment when we realized that this was it for the wild individuals of this tree (on Oahu),” Hynson recalled. Down the mountain in the Nanakuli Valley, school children still sing cultural songs about their “flower of the valley,” which is more of a requiem than an ode to the beloved na’u tree, which is no longer on their island.

The same overarching pattern of biodiversity decline is also occurring far beyond the shores of the archipelago. “Hawaii is a microcosm of the larger world,” Opgenorth says. Almost half endangered and threatened American plants are located in Hawaii. Globally, estimated 40 percent land plant species are at risk of extinction.

However, if mycorrhizal inoculation of na’ works, it could serve as a template for a strategy to save other endangered flora. In this way, Hawaii will become a shining example of ecological restoration for the rest of the world. “If we can solve the situation in Hawaii and find a way to live more sustainably,” adds Opgenorth, “it will resonate and there will be lessons that others can appreciate beyond the islands.”