Certain fungus keep rain forests from losing its plant diversity, study says

A new study has revealed that fungi, often seen as pests, play a crucial role policing biodiversity in rain forests.

The Oxford University-led research found that fungi regulate diversity in rain forests by making dominant species victims of their own success. Fungi spread quickly between closely-packed plants of the same species, preventing them from dominating and enabling a wider range of species to flourish.

“In the plant world, close relatives make bad neighbors,” said Owen Lewis of Oxford University’s Department of Zoology, who led the study. ‘Seedlings growing near plants of the same species are more likely to die, and we now know why. It has long been suspected that something in the soil is responsible, and we’ve now shown that fungi play a crucial role. It’s astonishing to see microscopic fungi having such a profound effect on entire rain forests.

‘Fungi prevent any single species from dominating rain forests as they spread more easily between plants and seedlings of the same species. If lots 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. Plots sprayed with fungicide soon become dominated by a few species at the expense of many others, leading to a marked drop in diversity.’

The study, published in Nature, looked at seedling plots across 36 sampling stations in the Chiquibul Forest Reserve, Belize. It was carried out by scientists at Oxford University and Sheffield University and funded by the Natural Environment Research Council.

Researchers sprayed plots with water, insecticide or fungicide every week for 17 months. They found that the fungicide dealt a significant blow to diversity, reducing the effective number of species by 16 percent. While the insecticide did change the composition of surviving species, it did not have an overall impact on diversity.

“We expected that removal of both fungi and insects would have an effect on the tree species,” said  Rob Freckleton of Sheffield University, who co-led the study. ‘However what was unexpected was that removal of the fungi affected diversity, but eliminating insects didn’t. Ours is the first study to unpick the effects of the different natural enemies.’

Scientists had suspected that fungus-like microorganisms called oomycetes might also play a part in policing rainforest diversity, but this now seems unlikely.

The findings show that fungi play a vital role in maintaining the biodiversity of rain forests, preventing a few highly competitive species from dominating. It helps to explain why tropical rain forests are so much more diverse than forests in temperate countries.

“We suspect that the effect of fungi will be strongest in wetter, hotter areas because this is where they thrive,” said lead author Robert Bagchi, of Eidgenössische Technische Hochschule Zürich. “This has important implications for how rain forests will respond to climate change, which is often predicted to reduce overall rainfall making it harder for fungi to spread. Without fungi to keep species in check, we could see a significant knock-on effect and lose a lot of the diversity that makes rain forests so special.”

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