UK - Fungi could be used as a 'bio-fertiliser' with the potential to replace unsustainable mined phosphate in future, according to new research from the University of Cambridge.
The study shows that the interaction of roots with a common soil fungus changes the genetic expression of rice crops, triggering additional root growth that enables the plant to absorb more nutrients.
In addition to causing extra root growth, the mycorrhizal fungus also extends within crop roots, blooming within individual plant cells.
The fungus grows thin tendrils called hyphae that extend into surrounding soil and pump nutrients, phosphate in particular, straight into the heart of plant cells.
Plants 'colonised' by the fungi get between 70 to 100 per cent of their phosphate directly from these fungus tendrils, an enormous mineral boost.
The researchers hope that the fungi could be used as a 'bio-fertiliser' that ultimately replaces the need to mine phosphate from the ground for industrial fertiliser.
Finding a replacement for mined phosphate is a critical problem as the fertiliser can cause pollution, and the big phosphate mines are now depleted to the point where they are expected to run out in the next 30 to 50 years.
"The big question we are trying to answer is whether and how we can make use of the biofertiliser capacity of mycorrhizal symbiosis in modern and more high input agricultural settings, meaning more intensive farming methods.
"We need alternatives to phosphate fertiliser if we are to feed growing populations," said Dr Uta Paszkowski from the University of Cambridge's, who co-authored the research.
Cereal root architecture involves a few big, thickset roots called crown roots, from which all the smaller lateral roots spread out into the different layers of soil.
Researchers found that plants colonised by mycorrhizal fungi have a different genetic expression which causes the cell walls within crown roots to soften, triggering the growth of many more lateral roots which are able to suck in more nutrients, contributing to a healthier plant with a higher yield.
This is in addition to the phosphate provided by the fungal tendrils, which in effect act as extra roots themselves (in return for which, the fungus absorbs carbohydrate from the plant).
"Plant roots that have the capacity to explore the widest soil area absorb the most nutrients as a consequence and so are likely to have a greater crop yield.
"By finding out which parts of the genome are responsible for the best plant root systems we can start breeding for the best root architecture," said Ms Paszkowski.
"Designer crops with the best possible root systems will mean greater crop yield, which means more people fed."
The main hurdle for researchers to overcome is the self-regulation of plants, which means the fungi cannot be tested on an industrial scale alongside traditional fertiliser.
"Plants monitor their own nutritional state. If a plant has enough phosphate it will not allow fungus to enter root - so at the moment it's one or the other.
"We are working on ways to circumvent this blockage so we can allow symbiosis to contribute in agricultural practices in better developed countries," said Ms Paszkowski.
Mycorrhizal fungi are extremely common in all soils around the world, and are an ingredient in many 'bio' plant foods found in domestic garden centres, but have yet to be used for industrial agriculture.
The study is published in Proceedings of the National Academy of Sciences.
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