AIMS AND OBJECTIVES

The increasing interest in the quantity and properties of deadwood is relevant both to maintaining biodiversity and to global C dynamics in forested areas. However, the sensitivity of soil organic matter (SOM) to environmental conditions is still a matter of great debate. Indeed, the effects of climate on the decomposition of deadwood and its subsequent influence on SOM is far from being fully understood and detailed investigations are missing. Therefore, there exists a need to delve deeper into the pathways of the decomposition of deadwood, the products emitted into the soil and their incorporation and significance for the stable and labile organic C pool in soils.

Alpine areas have on the one hand stable organic matter with a very high age and on the other hand labile, young soils and consequently very reactive organic materials. Moreover, high-altitude ecosystems are predicted to experience a rapid warming in the future with distinct consequences for SOM quality and quantity, and/or for the activities of soil organisms. Nevertheless, up to now very little is known about the influence of multiple and interacting climate drivers on soil biological communities and their activities, as well as on the consequences for carbon- exchange feedbacks. All together this makes alpine areas an ideal setting so as to further study the interplay between climate, forests, deadwood and soils (Fig. 1).

Under this context, the main objective of the project focuses on a particular way of integrating plant organic matter into the soil: the decomposition of coarse woody debris (CWD) and their incorporation into SOM, through the biological activity of the topsoil. Within this framework, the HUMUS FORMS represent the heart of the integration of the involved mechanisms. This general aim is linked to the following general question: What are the principal functional links between climate, degraded CWD, soil properties and the activity of faunal and microbial communities affecting OM evolution, and what are their effects on the stabilisation of SOM?

More specifically, four operational objectives have been set out:

(1) Description of the system elements via the quantification of CWD; the morpho-functional description of humus forms; and the quantification and characterisation of SOM.

(2) Assessment of intra-compartment dynamic processes via the determination of processes and rate of CWD decomposition; the evaluation of mesofaunal activity in the soils; and the functional evaluation of microbial diversity in CWD and in the soils.

(3) Assessment of inter-compartment dynamic processes via the evaluation of the effects of CWD on soil organic matter; and the impact of climate on the morphology and functioning of humus forms.

(4) Modelling approaches via linking site specific characteristics (micro- and mesofauna, decay mechanisms) to humus forms; the extrapolation using the humus forms as the link; and combining regional and local CWD measurements, linking them with the humus forms.

More detailed information about the aforementioned objectives is provided in the section “Research Programme” in which an overview of the working packages (WPs) of the project is given.

To fulfil the aims and objectives of the project, empirical investigations and field experiments are ongoing so as to investigate the decay mechanisms involved along altitudinal sequences, reflecting climate zones, in the study area of Val di Rabbi (Trentino). The climosequence includes sites ranging from 1000 m to about 2400 m a.s.l, both on north- and south facing slopes (see sub-section “Multidisciplinary characterisation of the study sites”).

Furthermore, the following hypotheses have been proposed within the scope of the present project:

Communities of mesofauna (especially Enchytraeids) and microorganisms representing the decomposer system are highly sensitive to climate which gives rise to changes in SOM, C stabilisation and humus forms.

Soil biological activity is expected to differ between south- and north-facing sites and along the climosequence. These differences significantly affect CWD decay and its incorporation into the soil. Lowest biological activity and consequently CWD decay rates are expected at north facing sites close to the timberline.

CWD decay products will not or only to a very low degree affect the stable organic matter fraction due to the already existing strong organo-mineral associations. CWD will only affect the labile fractions, especially on north-facing sites.

Humus forms can be used for upscaling and the prediction of soil mesofauna and microbiota at local and landscape scales.

Fig. 1. Scheme of the system of interest showing the interplay between climate, forests, deadwood and soils. Outline made by Markus Egli.