Genetic basis of herbivory, litter decomposition and nitrogen cycling in birch forest
Silver birch, Betula pendula, is one of the most common tree species in Europe. It is a typical pioneer species that quickly colonizes open forest patches and can be dominant in early boreal forest succession. In 2008, we established a field site using cloned seedlings of 17 silver birch genotypes. Since then, we have been testing the significance of silver birch genetic variation in various community and ecosystem attributes of birch forests. Our results show how natural selection has a potential to act on communities and ecosystem functioning through plant genetic variation. Our main findings are:
- B. pendula populations have high genetic variation – our results suggest that this variation is not maintained by small-scale forest ground heterogeneity;
- the genetic variation of leaf autumn coloring can explain the variation in autumn aphid load among silver birch individuals;
- the genetic variation in secondary metabolites remains through leaf senescence and litter decomposition, but no genetic effects on microbial growth and litter decomposition appear;
- insect herbivory effects on leaf litter mass loss are genotype-specific;
- the genetic variation in nitrogen resorption efficiency controls nitrogen dynamics in decomposing leaf litter.
This project was funded by the Academy of Finland.
Plant-herbivore-decomposer interactions and nitrogen cycling in grasslands
We have been testing the theories and mechanisms of plant-herbivore-decomposer interactions in various grassland set-ups for over ten years. Our main findings are:
- live roots and litter of different plant species can induce development of different decomposer communities in the soil;
- effects of aboveground herbivory and defoliation can propagate through several trophic levels in the soil;
- in sub-arctic grasslands, where nutrient mineralization rates are inherently slow, herbivore-induced changes in soil communities can affect plant growth via reduced nitrogen mineralization;
- in more fertile soils, defoliation-induced reduction in soil nutrient availability may be negligible and have no role e.g. in those grassland restoration practices that rely on mowing;
- large herbivores can effectively control plant community structure and plant ecophysiology through defoliation and drive grassland functioning by increasing the patchiness of soil nitrogen availability.
The grassland research was funded by the Academy of Finland and EU. We were a partner in two EU funded networks, one focusing on the conservation of soil organism diversity under global change (CONSIDER), the other on the role of rhizosphere interactions in controlling plant community structure (BIORHIZ).