Fluxes, pools, and turnover of C within the fine root systems of individual trees at a natural forest stand

13C-puls on silver firs. Foto: Tina Endrulat (WSL).

Objectives

Roots fulfill important functions for vascular plants; they take up water and nutrients from the soil, they provide physical stabilisation, and they store carbon (C) compounds. In forest trees, roots also are involved in symbiotic relationships with ectomycorrhizal fungi where carbohydrates are exchanged against nutrients (Brunner 2001). To support these functions, large amounts of carbohydrates are transported from trees above-ground parts to their roots. Up to one third of the net primary production are invested into the formation of fine roots (<2 mm in diameter) (Jackson et al. 1997) which itself are the most active and dynamic part of the root system in terms of nutrient uptake and storage (Trumbore and Gaudinski 2003). After a mean of 2 to 5 years, however, these fine roots die and underlie decomposition and mineralisation. Thus, fine roots are large below-ground nutrient and C sources when fine roots are turned over and decayed. Below-ground C fluxes, however, are still not well understood because fine roots are qualitatively and quantitatively difficult to investigate in situ.

Aim

The proposed project has the aim to investigate fluxes, pools, and turnover of C within the fine root systems of individual trees over time and space. Such an aim, however, can only be reached after the fine root systems of genetically distinct tree individuals have been previously mapped, and after a stable C isotope pulse has been applied to the canopies. The various forms of labelled C, from fine roots respired CO₂ as well as non-structural and structural carbohydrates within the fine roots, recorded shortly before and after the C pulse at various times and at various distances to the stems will give important information about the contribution of individual trees to the soil C and its dynamics.

Methods

1. Mapping of the below-ground population structure of distinctly different silver fir (Abies alba) individuals at a natural forest stand on the Swiss Plateau (LWF-Vordemwald) with microsatellite markers according to the method of Brunner et al. (2004).
2. Stable C isotope (13C) - pulse to the canopies of selected tree individuals over a short time period.
3. Recording the below-ground labelled C by soil respiration measurements and by fine root sampling at various times before and after the labelling and at various defined distances to the stems. d13C (13C/12C)-measurements with IMRS include fine roots respired CO₂ as well as non-structural and structural carbohydrates such as starch and cellulose.
4. Measuring d13C of the surrounding fruiting bodies of ectomycorrhizal fungi and of the tree seedlings within the rooting area of the labelled trees in dependency on time and distance to the stems.

Relevance for extension

Carbon sequestration in forest soils is one of the main issues of the forest ecosystem research. However, it is still insufficiently investigated how tree individuals, depending on their dominance stage, health, or age, contribute quantitatively and qualitatively to the soil C pool. The proposed project has the aim to investigate fluxes, pools, and turnover of C within the fine root systems of individual trees over time and space. The results of this study can improve ecosystem models, which include C sequestration of forest soils by taking into account the dominance stage of individual trees.

Finances

This project is financially supportet by the State Secretariat for Education and Research, and by COST E38 'Woody root processes'.

Recent publications

Brunner I, Godbold DL. 2007. Tree roots in a changing world. Journal of Forest Research 12, 78-82.

Contact persons

• Ivano Brunner