Big Idea of 2014: The Next Green Revolution, Powered by Microbes

With the double threat of decreasing crop yields and a 35% surge in food demand over the next century, no idea in agricultural science can be too big or too audacious.

One technique that’s been tossed around for decades, but never successfully implemented, is the directed, selective breeding of a plant’s microbial support system. Soil microbes function similar to the human microbiome—they defend against harmful antigens and help access important nutrients. Mycorrhizal fungi, in particular, have an ancient symbiotic relationship with plants—for hundreds of millions of years, they’ve been exchanging water and nutrients for access to carbohydrates, and they are present around the root systems of 80–90% of agricultural crops.

mycorrhizal-network
Mycorrhizal fungi colonize the tip of a root, seen here under magnification.

Cynthia Graber reported on this microbial frontier for NOVA Next back in June:

Farmers have manipulated the plant-microbe relationship, unknowingly, for thousands of years. Compost, for example, does not simply contain beneficial nutrients—it also teems with living organisms, as does animal manure. Crop rotation, too, can enhance microbial diversity. Stalks and crop remains left on the field or plowed into soil provide microbes with food. And growing particular plants together—such as the traditional grouping of bean-squash-corn in the early Americas—does the same, as each plant likely contributes a complementary set of microbes.

But, for the most part, the tightly braided relationship hasn’t yet factored into the workings of modern agriculture. Today, if a plant needs more of anything, we just add it—water, nitrogen, phosphorus, manganese, and so on. In the 20th century, this approach produced an abundance of crops and staved off starvation for millions. But it has also soaked groundwater with nitrogen, led to algal blooms in lakes and rivers, and spawned a massive dead zone in the Gulf of Mexico. Studies show that nitrogen fertilizers can also reduce the diversity of microbial life. Pesticides can be more harmful. Even tilling cleaves fungal networks. Until recently, we knew little about how we’ve been inadvertently crippling our crops’ complicated support network.

Ian Sanders of the University of Lausanne in Switzerland thinks he can tweak the soil’s microbial ecosystem to significantly boost crop yields. He is breeding custom varieties of fungus species that he hopes will foster more robust plant-fungi relationships. In other words, the next green revolution may not rely on improved crops or better fertilizers, but on the offspring of select soil fungal strains.

Sanders and a team of scientists traveled to Colombia to test their hypothesis on cassava, a white root that’s a staple for nearly a billion people across the globe. Like many other tropical plants, cassava has trouble securing phosphorus, and mycorrhizal fungi are especially adept at helping plants access it. The team has been analyzing test fields for months, noting which breeds of the fungus lead to bigger harvests. Elsewhere, other researchers are looking into other ways of modifying root microbiomes.

Tapping into this support network could eventually result in what Sanders calls an “association map:” a comprehensive listing of fungi and crops genomes along with their corresponding environments. It would allow farmers to pick the best microbes for a given crop in a certain part of the world, potentially leading to more bountiful harvests. Such a map could help us navigate a future of surging demand and uncertain yields.