The role of plant root exudates in the acquisition of biolimiting nutrients at early stages of soil development

Fig. 1: Top view of Damma glacier forefield (picture: Jörg Luster, WSL).

Fig. 2: Sampling of soil solution at a 6 year old site from the rhizosphere of Rumex scutatus (picture: Jörg Luster, WSL)

Fig. 3: Treatment of Rumex scutatus, Rumex alpestris and Oxyria digyna in rhizoboxes in the climate chamber (picture: Hans Göransson, ETHZ)

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 (in close collaboration with the "Plant Ecology" group, ETHZ) aims at demonstrating the relative significance of plant root exudates (low molecular weight organic acids, phenolic compounds, ...) 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 key plants in rhizoboxes filled with quartz sand (Fig. 3). Phosphorus nutrition treatments include different solid P sources and PO4 concentrations in the irrigation solution. Soil solution was sampled using different methods including micro tension lysimeters placed in the vicinity of root tips and lateral roots, collection of percolate at the bottom of the rhizoboxes, and, at the end of the treatments, application of filter papers to the roots and short-term treatment of individual roots in vials filled with doubly-deionised water.

• Analysis of collected soil solutions for low-molecular weight organic acids using ion-chromatography, phenolic substances using HPLC
  

Collaboration

WSL: “Soil Sciences” (Jörg Luster), "Central Analytical Laboratory" (Alessandro Schlumpf), “Wetlands” (Edward Mitchell), "Snow Hydrology" (Jan Magnusson)

ETHZ: “Plant Ecology” (Hans Göransson, Harry Olde Venterink, Peter Edwards), “Plant Nutrition” (Emmanuel Frossard, Jan Jansa, Else Bühnemann, Monica Welc, Federica Tamburini), "Climate Geology" (Rienk Smittenberg, Stefano Bernasconi), "Environmental Geochemistry" (Gerhard Furrer), "Soil Chemistry" (Jan Wiederhold), "Isotope geochemistry and mineral resources" (Emmanuel Lemarchand)