Impacts of ectomycorrhizal fungi (P. involutus) on resistance and resilience to drought stress of Pinus sylvestris and Quercus petraea growing in single and mixed-species communities

Details

Supervisors

Declerck, Stephan ; Ponette, Quentin

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en gestion des forêts et des espaces naturels, à finalité spécialisée

Abstract

Due to climate change, droughts are becoming increasingly frequent and severe. This exerts substantial pressure on forest ecosystems, necessitating the implementation of new forest management strategies to adapt forests and enhance their resistance and resilience to drought. Among these strategies, natural regeneration through mixed-species seedlings combined with ectomycorrhizal fungal associations emerges as an appealing solution. Species mixture can enhance tree stress resistance and expedite post-stress recovery, especially in the context of drought, through niche complementarity among certain species. Ectomycorrhizal fungi, on the other hand, are known to form symbiotic relationships with tree roots in most forest ecosystems, aiding in drought mitigation by facilitating water and nutrient absorption. However, the majority of studies examining the effects of species mixture and ectomycorrhizal fungi on tree drought resistance and resilience primarily focus on mature trees. Seedlings, due to their limited reserves and underdeveloped root systems, are more vulnerable to drought stress. This master thesis aimed to evaluate the impact of the presence of the ectomycorrhizal fungus Paxillus involutus and species mixture on the drought resistance and resilience of Pinus sylvestris and Quercus petraea seedlings. The results primarily revealed competition between the two species, resulting in better growth of oak seedlings in the mixed treatment, while pine seedlings displayed reduced growth. This appears to be attributed to competition for water access, driven by the small pot size and significant root system developmental differences between the two species. Light competition could have also influenced the interactions between the two species. However, the mixture did not seem to impact seedling resilience. Nonetheless, pine seedlings exhibited better drought resistance and resilience than oaks, owing to their isohydric strategy and root system plasticity. The impact of ectomycorrhizal association could not be established due to very low mycorrhization rates. This was likely due to high temperatures in the greenhouse during seedling growth, leading to fungal decline. However, substantial mycorrhization appears to have slightly affected oak seedlings, reducing their growth and weakening them, making them more susceptible to drought. The study's findings underscore the intricate nature of interspecific interactions between seedlings and ectomycorrhizal fungi, emphasizing the significant influence of the environment on shaping these interactions. For future research, conducting experiments in larger containers to avoid competition between seedling and in more controlled environments to prevent fungal decline would provide valuable insights. Additionally, under optimal conditions, exploring the experiment with different species, strains, and more complex mixtures of trees and fungi could yield further insights into the evolution of these interactions.