Metla Project 3361

Mechanisms of resistance of forest trees

Duration: 2002-2006 Keywords: abiotic resistance, biodiversity, biotic resistance, climatic adaptability, climatic change, flowering of forest trees, growth
Research project group: Distinct projects 1 - Structure and function of forest ecosystems

Objectives

This project will study the mechanisms of tree resistance to herbivores (insects, mammals and pathogenic fungi), and abiotic threats, and, moreover, how resistance is related to economically important life history traits of trees. We are mainly interested in white birch and will study how fitness is related to seed set, phenology (leaf out, growth termination), growth and abiotic resistance (to ozone, UV, temperature, CO2) and biotic resistance (mammals, insects and pathogenic fungi). This is mostly basic research. The practical aim is to increase the changes of seedlings to survive and grow well as plantation trees in various environments and to develop methods for commercial use of secondary metabolites of trees. In addition to birch also Salix spp, Populus, Larix spp and Pinus sylvestris will be used in the experiments.

Results

We examined the mechanisms and genetics of abiotic and biotic resistance of birches and willows, and especially we were interested in trade-offs between life-history traits of these species. Research was carried out in natural forests, field and greenhouse experiments.

In natural populations of Silver birch there is large genetic variation in resistance to hares and voles, but also environment has a strong effect on resistance. In addition, competitive interactions have an effect on this variation: in dense stands the voles and hares select fast growing seedlings. In low competition practical plantations, the fastest growing seedlings are most resistance. In addition, fast growth allows seedling escape from ground-feeding mammals.

Silver birch genotypes are chemically quite variable, and also the fertility of the site has an impact on quantitative chemical characters of the birch leaves. Hares avoid resinous shoots, and the triterpenoids in the resin droplets of the shoots are metabolically expensive for the plants. It is likely that the main function of those droplets is the protection of shoots because the terpenoid content in seedling shoots, which hares can reach, is 100 times higher than in shoots of mature birches.

Intraspecific variation in timing of bud burst and start of growth period is considered important not only for growth capacity but also for resistance to several herbivorous insects, which have specialized in birch leaves. Contrary to expectations, the trees with early bud burst don’t show faster growth. For growth maximization, the continuation of growth late in the autumn seems far more important. But may lead to increased difficulties in winter-hardening processes.

Ozone toleranze of birch genotypes is also highly variable. Some genotypes reduce the intake of ozone by decreasing the stomatal conductance, but this strategy seems lo lead to decreased growth. Some genotypes produce protective antioxidants. Moderate ozone increases lead to increased shoot growth but to decreased root/shoot ratio, thus seedlings may be disposed to other abiotic hazards.

Willows may be used for herbal medicine production, the most famous example being aspirin. Salicin mostly accumulates in willow bark, buds and young leaves. Especially high salicin content is found in dark-leaved willows (S. myrsinifolia), but the variation among clones of myrsinifolia is also very large. By using plastic mulch the growth of willow cuttings can be increased considerably, and mulch has a negligible effect on the bark salicin concentration. Consequently, by selecting best clones and cultivation methods, the salicin production can be increased dramtically.

Co-operation with University of Joensuu, Faculty of Biosciences, was very fruitful. Three PhD thesis were completed (Variation in secondary chemistry within a natural population of birch: Effects of genotype, environment and ontogeny by Marja-Leena Laitinen; Variation in the survival, growth and resistance responses of white birches by Jaana Laitinen and The effects of drought stress and enhanced UV-B radiation on the growth and secondary chemistry of boreal conifer and willow seedlings by Satu Turtola) for University of Joensuu, professors Riitta Julkunen-Tiitto and Jorma Tahvanainen. During the period of 2002-6 this project produced 27 peer reviewed international publications.

Project leader: Rousi, Matti
The Finnish Forest Research Institute, Vantaa Unit, PL 18, FI-01301 VANTAA, FINLAND
Phone: +358 29 532 4230
E-mail: matti.rousi@metla.fi

Other researchers: Henttonen, Heikki, VA (2004), Huttunen, Liisa (2005), Yamaji, Keiko (2002)

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Updated 12.06.2012
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