BigLink-SoilSolution

This project is part of the multidisciplinary CCES project BigLink (“Biosphere-Geosphere interactions: Linking climate change, weathering, soil formation and ecosystem evolution”). It studies the plant-soil-microbe interactions at early succession stages in the Damma glacier forefield occurring in response to limited nutrient availability, in particular the role of root exudates.

Objectives

The BigLink project studies initial weathering in the Damma glacier forefield (Fig. 1) situated at the south-western end of the Göscheneralp valley. This subproject

• Investigates the interactions between the vegetation with its associated microorganisms and the soil in order to access nutrients.

• Assesses the importance of these interactions at different succession stages for mineral weathering.

In particular, the WSL-soil sciences contribution  aims at demonstrating the relative significance of low molecular weight organic acids – released by plant roots and microorganisms - in mobilising limited nutrients like P and K.

Methods

• In the field, at selected plots of the chronosequence, collection of soil solution from the rhizospheres of selected key plants and from bulk soil (no plants at young plots and non-specific grass vegetation at older plots), using micro tension lysimeters (Fig. 2).

• In the climate chamber, treatment of selected alpine pioneer plants in rhizoboxes filled with quartz sand or soil (Fig. 3) under different conditions with respect to P availability.

• Analysis of collected soil solutions for low-molecular weight organic acids using ion-chromatography and for metal concentrations by ICP-MS.

Results

• Overall and independent of soil age, soil type and sampling date, net mobilisation of P and metals correlated with the net production of carboxylates, with malate, tartrate, oxalate and citrate playing specific roles (Luster et al., in prep.).
• Once first plants appear, they seem to strongly increase nutrient release from minerals in their rhizosphere with root exudation of carboxylates probably playing a two-fold role. On one hand it stimulates microbial activity, on the other hand contributes directly to weathering, in particular by means of ligands that are not produced by microorganisms such as tartrate. (For results on mobilisation by roots and fungi see project “Microbial colonization and its effects on mineral weathering”)