Viruses, bacteria, fungi… not many good things come to our mind when we think about these organisms. Only during the last decade, it dawned on us that these organisms can actually be beneficial to our health. Our gut bacteria, for example, are required for training our immune system. Without microorganisms we would neither be healthy nor happy. The same is also true for plants. Microorganisms rule the plant world. Understanding how viruses, bacteria and fungi affect plants – not only in disease – but especially in health can help us feed the world, sustain biodiversity and fight climate change.
Today, I would like to focus on a special fungus which has the unpronounceable name “arbuscular mycorrhiza”. This fungus consists mostly of a network of thin filaments – called hypha – spreading through the soil. The hypha of these fungi can drill holes into the plant roots and organise a structure (“haustorium”) inside the plant, which serves as a market ground for plant and fungus. What do they exchange? Well, the plant sells sugars which are an important source of energy for the fungus. On the other hand, the fungus has nutrients and water on offer that it transported from distant places via its hyphal network directly to the plant root. Both, plant and fungus, profit from each other. This relationship is called “symbiosis”. Virtually every single plant lives in symbiosis with fungi. Without this little market in the plant’s root, the plant has to struggle much harder to survive.
In order to feed the world, we currently use an area of the size of South America for cropland and an additional area of the size of Africa for grazing land. 7.8 billion people live on the Earth – 1 billion of these are undernourished. The world population is estimated to grow to 9 billion by 2050. Population growth, production of biofuels, higher living standards going in hand with more meat and dairy production, … all of this is expected to require another area of a size similar to the size of Canada to be transformed to agricultural lands until 2050. This change will especially occur in the tropical countries where the population is growing the strongest, where biofuel crops are preferentially cultivated and where there are still wild places to be transformed. It comes therefore to no surprise that the Amazonian rain forests are burning and that biodiversity dwindles away.
Agriculture needs to be efficient while using services provided by nature to have minimal impact on tropical ecosystems. Lowland tropical soils come with a problem: they are very low in phosphate. Phosphate is an essential nutrient needed by plants to grow. In intact tropical forests, phosphate is bound in a closed nutrient cycle. It is bound in plant tissues. When this tissue decomposes, the phosphate is directly taken up again by the next species. Unfortunately, when cropland is established, the phosphate is washed away and the phosphate cycle is disrupted. The cropland will be degraded after only short use and can only be used by extensive use of fertilisers afterwards. This is exactly where our little friend mycorrhiza could help. With its extensive hyphal network, it can transport phosphate directly to the crops’ roots and make it available to the plant. It is as if you hired a babysitter to feed your ever-hungry baby.
Why then have we not heard of mycorrhiza more often? Most importantly, the beneficial use of mycorrhiza was overseen for a long time, since the research conducted by rich countries was mostly done on fields in the temperate climate where phosphate is not such a limiting nutrient as in the tropics. Today, the beneficial effect in the tropics is known. However, the ecology of mycorrhiza species needs to be carefully analysed before using them safely. Mycorrhiza that is beneficial for one plant species could turn out to be parasitic for another species. In addition, only recently it was discovered how to cultivate mycorrhiza in the lab in order to establish defined formulations that can be applied to the field.
These are challenges that can only be overcome by investment, research and innovation of rich and poor countries together. Sincere claims to protect tropical rainforests consequently requires researchers, farmers, industry and governments from the global South and North to work together.
To continue reading the scientific sources:Laurance WF, Sayer J, Cassman KG. Agricultural expansion and its impacts on tropical nature. Trends Ecol Evol. 2014 Feb;29(2):107-16. doi: 10.1016/j.tree.2013.12.001. Epub 2013 Dec 30. PMID: 24388286.
Rodriguez A, Sanders IR. The role of community and population ecology in applying mycorrhizal fungi for improved food security. ISME J. 2015 May;9(5):1053-61. doi: 10.1038/ismej.2014.207. Epub 2014 Oct 31. PMID: 25350159; PMCID: PMC4409159.
Click here for very informative website of Ian Sanders’ research group who is working on the mycorrhizal symbiosis.
Hallo Nils,
heißt das, kennt man die Bedinungen für das Gedeihen des Mycorrhiza und damit die Lösung für
das Phosphat in der subtropischen Landwirtschaft, dann ist der Untergang des Regenwaldes besiegelt? Die Folgen für das Klima wären katostrophal. Oder habe ich da einen Denkfehler?
Mit lieben Grüßen aus dem sonnigen Eitorf
Dein Papa
lieber Nils
war aber ein kurzer Artikel, interessant ,dass es vielleicht doch etwas zu entdecken gibt um unsere Erde und die Menschen weiter bestehen zu lassen.
Gruß deine Mama