Ancient partnerships abandoned when alternatives emerge

Even the most ancient cooperative partnerships that have survived for hundreds of millions of years, can break down when new options in nature arise.

05/02/2018 | 2:01 PM

Unseen to us, almost all plants on planet earth form belowground partnerships with beneficial soil microbes. One of the most important is between plant roots and a type of soil fungi called arbuscular mycorrhizal (AM) fungi. The fungi form networks in the soil and provide the plant with soil minerals, such as phosphorus and nitrogen. In return, the fungi receive sugars from the plant. This cooperation between plants and fungi is crucial for plant growth, including of many crops. Plants sometimes even get up to 90% of their phosphorus from these soil fungi.

Reconstruct the evolutionary history
In a new study, published in the journal PNAS, an international team of researchers including scientists from VU’s department of Ecological Science have developed and analysed an enormous database of plant-fungal interactions containing thousands of species. They used computer models to reconstruct the evolutionary history of the partnership, and found that cooperation between plants and fungi has been lost about 25 times, despite their potential benefits.

Lead author and former VU PhD student Gijsbert Werner explains: “Despite having successfully cooperated for over 350 million of years, we find that partnerships among plants and soil fungi can break down completely”. “At first we didn’t believe that such an ancient and important collaboration could be abandoned so many times”, says co-author and professor of Mutualistic Interactions Toby Kiers.

Why cooperation breaks down
The scientists then studied why cooperation breaks down. They found that in most cases the plants were replacing the fungi with another cooperative partner, who did the same job, either different fungi or bacteria. In the other cases, plants had evolved an entirely different way of obtaining the required minerals – for instance, they had become carnivorous plants which trap and eat insects.

“Our results show that crucial cooperation among different species can be lost, but only if plants find a new way to get their nutrients”, adds Werner. “In some environments, other partners or strategies are likely to be more efficient sources of nitrogen or phosphorus, driving a breakdown of previously successful cooperation between plants and AM fungi”.

Werner Figure 1

Werner Figure 2.