Toxic air is causing malnutrition in trees

The News

  • According to new study, air pollution from farms, diesel engines and factories is leaving trees malnourished and causing alarming levels of disease in British trees.


Key findings

  • The study indicates that there is an alarming trend of tree malnutrition across Europe, which leaves forests vulnerable to pests, disease and climate change.
  • The study, published in the Nature, examined 40,000 roots from 13,000 soil samples at 137 forest sites in 20 European countries for a period of 10 years to determine the fungi’s tolerance to pollution.
  • The concerning trend may be due to the loss of mycorrhizal fungi.
  • Toxic levels of nitrogen in rainwater appear to be breaking up ancient fungal highways, known as the “wood-wide web,” through which trees exchange essential compounds.
  • Between 15 and 90 percent of forests in the UK are thought to be stricken by pollutants that trickle down into the soil.
  • It has been found that the air pollution is causing ‘malnutrition’ in trees by harming beneficial fungi in the roots.
  • The signs of malnutrition can be seen in the form of discoloured leaves and excessive falling of leaves.


Impact of study

  • The study could be a precursor to design new fungal monitoring systems.
  • Conventional conservation policies do not typically protect fungi, which makes it difficult to assess which species are rare or declining.
  • The results should be used to design new studies into the link between pollution, soil, mycorrhizae, and tree growth.


About Mycorrhizal fungi

  • If we observe roots of a plant with a microscope, we will find round structures and fibers closely associated with the fine rootlets and root hairs. These are root fungi, or mycorrhizae.
  • Mycorrhizal fungi is hosted by the trees in their roots to receive nutrients from the soil.
  • Some mycorrhizae, called ectomycorrhizae, have hyphae that press closely against the outer side of the walls of root hair cells.
  • The endomycorrhizae, by contrast, actually send hyphae through the root cell walls and into the space between the cell wall and the plasma membrane.
  • The association between mycorrhizal fungi and plants is beneficial to both partners.
  • The fungus extracts phosphorus, nitrogen and potassium from the soil and releases them inside the roots of the plant.
  • The additional nutrients that the plant receives from the fungus allow it to grow faster and larger.
  • The mycorrhizal fungus, some of which are known for forming truffles and mushrooms, benefits by drawing sugar from the plant, which it uses to support its own cellular respiration.
  • This plant-fungal symbiotic relationship is crucial for the health of the tree.



Factors that determine the presence of fungi

The most important predictors of which species of mycorrhizae fungi would be present and their numbers are

  • The characteristics of the tree like species and nutrient status
  • Local environmental conditions like the atmospheric pollution and soil variables


Effect of high levels of nutrients as a result of air pollution

  • High levels of the nutrition elements like nitrogen and phosphorus in the mycorrhizae changes them to act as pollutants rather than nutrients.
  • These pollutants threaten mycorrhizal fungi because they can be “outcompeted by those that are more tolerant of pollution.
  • The tougher fungi, which return fewer nutrients, make the tree suffer from a lack of nutrition.


Way Forward

  • As a result, researchers say legal limits on air pollution are set too high and need to be reduced.
  • High levels of nitrogen – which enters soil due to agricultural runoff, industrial activities and wastewater – are particularly harmful.
  • Therefore the current European nitrogen limits may need to be cut by half.
  • This is already being done in North America where the limits are set much lower.


Additional Info: About fungi in general

  • Fungi are eukaryotes having the cellular components of both animal and plant cell
  • Animal cell characteristics: Nuclei, mitochondria, an endo-membrane system, and a cytoskeleton.
  • Plant cell characteristics: They also have cell walls, but the cell walls, instead of including cellulose, as in plants, are made of the carbohydrate chitin, a chemical also important in producing the exoskeleton of insects.
  • Some fungi like the yeasts live as individual cells but most of the other fungi are multi-cellular

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