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From Wildlife Extra:
Microscopic fungi is revealed as the crucial factor in regulating diversity in the world’s rainforests
An Oxford and Sheffield Universities joint research team has discovered that fungi regulate diversity in rainforests by making dominant species victims of their own success.
“In the plant world, close relatives make bad neighbours,” said Dr Owen Lewis of the Oxford University Department of Zoology. “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 was 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 rainforests.
“Fungi prevent any single species from dominating rainforests as they spread more easily between plants and seedlings. If lots of plants from one species grow in the same place, fungi quickly cut their population down to size, levelling 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 in Belize. Researchers sprayed plots with either 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 per cent. 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 Professor Rob Freckleton of Sheffield University. “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.
“Oomycetes are potent pathogens that can cause seeds and seedlings to rot, and were responsible for the 1840s potato famine,” said Professor Sarah Gurr, formerly of Oxford University and now at the University of Exeter. “To see if they play a role in promoting rainforest biodiversity, we sprayed plots with Ridomil Gold, which protects plants against oomycetes. It had no significant effect on the number of surviving species, suggesting that true fungi and not oomycetes are driving rainforest diversity.”
“We suspect that the effect of fungi will be strongest in wetter, hotter areas because this is where they thrive,” said Dr Robert Bagchi, who began the study at Oxford and completed it at ETH Zurich. “This has important implications for how rainforests 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 rainforests so special.”