Mycorrhiza - a key factor for tree recruitment after forest fire?

Background information and research questions

Can mycorrhizal fungi survive a forest fire and recolonize a burnt site after fire?

How does mycorrhizal fungi diversity influence the performance of Pinus sylvestris seedlings under drought stress? Photos: T. Kipfer (WSL)

Due to climate change mean annual temperatures are predicted to dramatically increase for the next hundred years. In dry parts of Switzerland, e.g. in the inner-alpine valleys, higher temperatures in summer will result in higher frequencies of dry periods during the growing season. A possible consequence is that forest fires will occur more frequently in the future, especially in Pinus sylvestris forests on the shallow, southerly-exposed slopes. Thus the question arises whether and how trees recover from fire disturbance and recolonize a forest fire site. It is well known that symbiotic fungi, so-called mycorrhizae, enhance seedling growth by improving water and nutrient uptake. But also mycorrhizal fungi diversity is thought to be diminished by fire, and thus the positive relationship between plants and fungi may be at risk.

This project addresses the following questions:

1. To what extent can mycorrhizal fungi survive the high temperatures during a forest fire, and how rapid can they recolonize a burnt site after fire?
2. How does mycorrhizal fungus diversity influence the performance of Pinus sylvestris seedlings under drought stress?

Methods

The first question is addressed by a combination of a field study and a reductionistic experiment. Different forest fire sites in the Valais and the Aosta valley are sampled and investigated in terms of mycorrhizal diversity. Additionally, soil samples are heated at different temperature levels in a drying oven and subsequently, mycorrhizal diversity is assessed.

To tackle the second question, a greenhouse experiment is performed. Pinus sylvestris seedlings are grown in sterile soil, and then inoculated with different numbers of fungus species. After a drought period of five months, the seedlings are harvested and analyzed in terms of shoot and root growth and storage of nutrients in the needles.

These results are supposed to improve our understanding of below-ground processes influencing the recolonization of a forest fire site.

Contact

• Simon Egli
  

• Thomas Wohlgemuth