Almost all plants live in close symbiosis with so-called mycorrhizal fungi—an important symbiosis for absorbing essential nutrients. In their new study, a team led by ecologist Christina Kaiser from the Center for Microbiology and Environmental Systems Science (CeMESS) at the University of Vienna has now discovered that this mycorrhizal symbiosis is very sensitive to imbalances of certain nutrients (nitrogen, phosphorus and potassium) in the soil.
The data come from a 70-year long-term study and therefore provide particularly valuable insights, enabling scientists to make a significant contribution to sustainable agriculture. The results have recently been published in New Phytologist.
Mycorrhizal fungi colonize plant roots and grow a network of fungal hyphae into the soil from there. These fungal hyphae are much thinner than plant roots and can grow into even the finest soil pores. This enables them to absorb essential nutrients such as phosphorus and nitrogen from the soil much more efficiently.
This is what makes them so valuable to their plant partners: the fungi pass on a large proportion of the nutrients they absorb to the plants in exchange for carbohydrates produced by the plants through photosynthesis. With a well-functioning mycorrhizal symbiosis, plants are able to grow relatively well even in nutrient-poor soils. Many of the plants used in agriculture today, such as wheat, maize and potatoes, also live in such a symbiosis. As in the wild, these fungi protect plants from pests and help them cope with water shortages in agriculture.
Data from a 70-year long-term experiment
In the current study led by the University of Vienna, scientists have now been able to show that mycorrhizal symbiosis is very sensitive to imbalances of certain nutrients (nitrogen, phosphorus and potassium) in the soil.
The data come from a measurement campaign conducted by Andreas Richter, also from the CeMESS at University of Vienna, in a long-term experiment that has been running for over 70 years at the Raumberg-Gumpenstein Agricultural Research Station in Admont (Styria). In this long-term experiment, grassland areas have been regularly mowed and harvested since 1946, with the nutrients removed by harvesting being replaced by various combinations and amounts of nitrogen, phosphate and potassium fertilizers.
The study authors found that potassium deficiency in combination with nitrogen fertilization had an extremely negative effect on the symbiosis: Under these conditions, the plants lost about half of their valuable fungal partners and thus, presumably, part of their natural shield against pests and dehydration.
Evidence of more sustainable use of fungal families
“We also discovered that within the largely unexplored spectrum of mycorrhizal fungi, there are families that specialize in specific nutrient situations,” says study leader Christina Kaiser from the University of Vienna. While certain fungal families responded positively to specific nutrient deficiencies, other families were severely decimated. Potassium deficiency, for example, reduced the proportion of fungi from the well-known Glomeraceae family, but at the same time increased the proportion of fungi from other, less well-known families.
“In agriculture, mycorrhizal fungi mixtures from this very family of Glomeraceae are currently mainly used. Our results suggest that fungi from other families should also be researched, as they may be better adapted to certain nutrient deficiency situations,” says Kian Jenab, doctoral student at the CeMESS at the University of Vienna and first author of the study.
Unbalanced fertilization has long-term effects on plant and soil health
The combination of low potassium and high nitrogen in the soil, which led to the greatest loss of mycorrhizal fungi in this study, is quite common globally—because potassium fertilizer is expensive and difficult to obtain in some parts of the world. As a result, potassium is often not fertilized sufficiently in relation to nitrogen.
“This unbalanced fertilization does not have an immediate effect on plant yield. However, it weakens the symbiosis between plants and fungi, which has long-term effects on soil and plant health,” Kaiser summarizes.
“The current study once again confirms the value of long-term experiments, which act as ‘silent observers’ of nature, documenting processes in our soils over decades and thus providing us with such deep insights,” adds Erich Poetsch, project partner at the Raumberg-Gumpenstein Research Station.
Provided by University of Vienna
This story was originally published on Phys.org.
