Doctoral candidate : Alexandre Fruleux
University / Institution : Université de Lorraine
Contract duration — Three years (2013-2016)
Research topic — Root development of interacting tree species
Research team and supervising scientists —
Équipe : Équipe ARBECO, UMR INRA-UL (1137) Écologie et Écophysiologie Forestières (EEF)
PhD supervisor: Damien Bonal
PhD co-supervisor: Marie-Béatrice Bogeat-Triboulot
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Context —
A large number of experiments have demonstrated that higher biodiversity levels improves ecosystem functioning which leads to ecosystem stability and greater ecosystem services. Mixed forests have been found to be more resistant to parasites (Castagneyrol et al, 2014), to show greater biodiversity (Branquart et al, 2010) and greater wood production (Morin et al, 2011).
Although these benefits seem to depend on many parameters and local conditions (Grossiod et al, 2014), they can be explained by two effects. The first, the selection effect (also know as sampling effect), states that including the most productive species in a mixture will increase the number of species therein. The second, known as the complementary effect, involves complementarity between species in aquisition and/or use of resources and results in niche separation or facilitation mechanisms (Loreau & Hector, 2001). Interaction mechanisms between tree species are currently poorly understood, specifically those which occur below ground level (Huang, 2001).
Objectives and specific questions to be addressed —
This thesis topic is structured around the following questions:
- Is root development influenced by interactions among species in mixed forests?
- Are interactions among species influenced by water availability through root development?
- How do the microbial communities change in response to different mixed conditions?
Scientific and socioeconomic issues — The Lorraine region is one of the most forested areas in France. Temperate forests are valuable from several perspectives (ecological, economic, recreational) but are currently at risk dues to global climatic changes. Our geographical region is expected to experience an increase frequency of droughts which may lead to increased competition for water and nutrients among forest species. In this context, promoting forest management practices that include higher species diversity might be a viable option. Improving our knowledge about the mechanisms that lead to positive effects in mixed forests, therefore, is an important issue for the Lorraine region.
Methodological approaches and expected results —
Two complementary experimental approaches will be used in this thesis study:
- Experiments in natural conditions (plantations) will allow us to study the impacts of interactions among tree species on water and carbon use, rooting depth, depth of water acquisition and diversity levels among soil microbial communities in various mixtures.
- Experiments in controlled conditions (pots in greenhouses, mini-rhizotrons) will let us address more detailed mechanisms: spatial distribution of roots and their growth rate while precisely controlling the availability of the resources.
The results should help us to better understand the nature of species interactions taking place in the soil in mixed forest stands, as well as their impact on growth and water and carbon cycles.
We chose to study species which naturally inhabit French forests and which are valued by forest managers for their high productivity and commercial value: beech, oak, maple and pine.
