Rainforests Can Thank Fungi for Their Good Looks

Why are rainforests such hotspots for life? Sure, they receive plenty of rain, obviously, and tend to be located in tropical areas that receive plenty of sunlight and heat all year. But it turns out that fungi, a category of life that’s known for sucking the life out of things, might be to thank for a rainforest’s incredible biodiversity.

There are lots of reasons why rainforests tend to have many more species of plants per hectare than any other place on Earth, but scientists have been stumped as to why no particular species seems to truly dominate a rainforest.

Certain species are more common, of course—a recent study found that just one percent of the Amazon’s tree species make up more than 50 percent of the total number of trees in the forest—but there is still an incredible 16,000 total species of trees in the Amazon, and a still unknown number of smaller plant species that make up the rest of it.

Researchers at Oxford University found that, without fungi, that type of diversity wouldn’t be possible. Fungi in the rainforest tends to spread very quickly between densely-populated individuals of the same species, according to a study published Wednesday in Nature. Without fungi, several types of plants would be much better suited to completely dominate large swaths of the rainforest.

“Seedlings growing near plants of the same species are more likely to die and now we know why,” said Owen Lewis, lead author of the study. “We’ve now shown that fungi play a crucial role. Fungi prevent any single species from dominating rain forests as they spread more easily between plants and seedlings of the same species.”

To test the theory, Lewis and his colleagues picked out 36 sampling plots across the Chiquibul Forest Reserve in Belize. Over the course of 17 months, they sprayed some of those plots with water, some with insecticide, and some with fungicide every week. The plots that were sprayed with fungicide saw the overall number of species living on them decrease by 16 percent. The plots that were sprayed with just insecticide had no change in biodiversity.

“If a lot of plants from one species grow in the same place, fungi quickly cut their population down to size, leveling the playing field to give rarer species a fighting chance,” Lewis said.

The finding is also supported by the fact that biodiversity tends to be best in spots closest to the equator, which tend to be some of the wettest parts of the world, according to co-author Robert Bagchi. “We suspect that the effect of fungi will be strongest in wetter, hotter areas because this is where they thrive," he said.

Rainforest biodiversity, especially in the Amazon, is incredibly important because species in the complex ecosystem tend to rely very heavily on each other, which allows for highly specialized species to evolve. For each plant, for instance, there are specific insects that prey on it, and then specific insects that prey on those specific insects, and so on. It makes for refuges of life unlike anywhere else on Earth, and such diversity can have direct human benefits as well, with the hunt for new medicines being a notable example.