Fine root turnover and decomposition as a component of ecosystem carbon budgets


Fine roots (diameter < 2 mm) are an important and dynamic component of forest biogeochemical cycling. Many previous studies on fine roots focussed on seasonal variability of fine root dynamics and on the effects of climatic differences between sites or of site characteristics such as nutrient availability. Relatively little is known about changes in fine root dynamics during the life cycle of a forest stand.
A primary objective of this present study is to determine fine root production and fine root turnover in four different stand age classes of two German chronosequence (Fagus sylvatica and Picea abies) sites. A chronosequence is composed of different stands within a forest area which can be distinguished from each other only by the difference in tree age. We hypothesize that fine root production will be higher in younger forests. Fine root production will be estimated in the present project by 1) evaluating previously obtained data from sequential soil coring and 2) installing, harvesting and elaborating of in-growth cores at the field. Nylon mesh bags will be installed in the soil and filled with a root-free substrate. Root growth into the bags gives an estimate of fine root production. Fine root turnover will be calculated as fine root production divided by earlier obtained data on standing fine root biomass.
A second objective is to compare the decomposition rate of tree fine roots (from the different age classes of both chronosequences) with the decomposition rate of roots of annual species. We hypothesize that a) the decomposition rate of tree roots will be higher in younger forests than in older forests, and b) that the decomposition of roots of annual species will be faster than the decomposition of tree roots. In a field experiment at one of the chronosequence sites, a fixed amount of fine roots will be incubated in soil of local origin and placed back into the soil in so-called decomposition bags. The root mass loss after harvesting estimates fine root decomposition. In a laboratory experiment, a fixed amount of tree roots of different tree age classes and roots of annual species will all be separately incubated in a fixed amount of local soil in glass sample tubes, and placed in a respirometer. The evolution of cumulative respiration will estimate root decomposition. In addition, we will attempt to use 14C analysis of root samples from all tree age classes from both chronosequences, in order to achieve an independent measurement of mean fine root age in these stands.
All results will be evaluated with the help of an ecosystem budget model. With this project, we expect to define appropriate methodology to estimate root turnover in forests and to obtain improved data on tree fine root longevity. We also expect to increase the understanding of the contribution of tree fine roots to soil carbon storage in young and in old forests. The project should also indicate whether forest management can contribute to increased carbon storage in soils by allowing forest stands to grow longer before harvest.

Principal Investigators
George, Eckhard Prof. Dr. (Details) (Plant Nutrition)

Duration of Project
Start date: 08/2003
End date: 08/2005

Last updated on 2020-10-03 at 16:40