Linking individual plant traits to ecosystem processes using a willow model system (ECOLINK-Salix)
Martin Weih & Petra Fransson
At present, we have a poor understanding of how individual genotypes added to an ecosystem create, maintain, and change biological diversity and ultimately affect ecosystem processes relevant for productivity, nutrient cycling and carbon sequestration. In this project, which started during 2013, we plan some field and growth container experiments to test the ecosystem consequences of adding individual genotypes of dominating plants, here trees and weeds. Thus, we want to functionally and quantitatively (including modelling) explore how the heritable traits of some genotypes of Salix (model system) affect (1) the diversity and function of understory vegetation; (2) the abundance and structure of associated mycorrhiza communities; (3) the action of herbivorous insects; and ultimately (4) ecosystem productivity and soil carbon (C) accumulation. Soil C accumulation is of particular interest for mitigation of the consequences of climate change. Apart from a better understanding of the functional links between individual plant traits and important ecosystem processes, the gained knowledge will help us to evaluate the consequences of introducing new plant varieties with different characteristics into agricultural or forest ecosystems. The research has implications for future bio-energy concepts, because new varieties of energy crops (e.g. Salix) generated by plant breeding must comply with the sustainability requirements (e.g. biodiversity, C accumulation) for a carbon-neutral and environmentally friendly energy source, e.g. Weih et al. (2014).
More specifically, in spring 2014 we planted a selection of willow varieties with well-known characteristics in field trials in Sweden (Uppsala, see photo above) and Germany (Freiburg and Rostock) and also in a controlled experiment (Uppsala); and we investigate the cascading effects of individual plant characteristics on understory plant diversity, trophic interactions and ecosystem processes related to productivity and soil C accumulation (see Fig.). The four varieties used are 'Björn', 'Jorr', 'Loden' and 'Tora', and the varieties are planted in monocultures and variety mixtures (two-, three- and four-variety mixtures).
Fig. Important links between individual plant traits (e.g. leaf area index; biomass allocation to roots, leaves and shoots; leaf phenology; leaf chemistry; nitrogen use efficiency) of a dominating plant (e.g. tree, here Salix, or weed) and ecosystem processes through trophic interactions. The lines indicate the relationships to be investigated in the proposed project. SOM soil organic matter.
Some specific hypotheses to be tested are:
- Genotype(s) having greater leaf areas promote different understory vegetation composition compared to the genotype(s) with smaller leaf areas;
- Genotypes with more efficient nutrient uptake and utilization promote ecosystem productivity and C accumulation potential;
- Genotypes with greater resistance to insect herbivores provide less resource inputs into soils of these relatively productive ecosystems and reduce C sequestration potential;
- Greater mycorrhizal colonization promotes soil C accumulation, along with effects on leaf chemistry and resistance to insect herbivores, which also feed back to C accumulation (see above);
- The above functional relationships combined, result in predictable effects of plant traits on ecosystem productivity and soil C accumulation (both can be easily assessed).
Participating institutions and researchers:
Swedish University of Agricultural Sciences: Martin Weih (project leader), Petra Fransson (co-leader; soil microbial ecology), Nils-Erik Nordh (field site management), Friderike Beyer (tree eco-physiology), Stefanie Hoeber (plant-plant interaction, litter decomposition), Carolyn Glynn (plant-herbivore interaction).
Stockholm University (Physical Geography and Quarternary Geology): Stefano Manzoni (biogeochemical cycling, modelling)
Karlstad University (Germany): Lutz Eckstein (weed dynamics)
Rostock University (Germany): Christel Baum (soil science and soil microbiology)
Torun University (Poland): Katarzyna Hrynkiewicz (soil microbiology)
The ECOLINK-Salix field sites are part of a global network of tree diversity experiments in which researchers collaborate regarding questions related to diversity and productivity in ecosystems dominated by trees, i.e. the TreeDivNet network (Verheyen et al. 2016).
Major part of the project is financed by the Swedish Energy Agency (project no. 36654-1).