Tree-Soil-Microbiome Interplay under Drought

Background

Major drought impacts are to be expected in several European inner-Alpine valleys, such as the Rhone valley of Switzerland, where climatic conditions have shifted towards increasing summer droughts due to higher evapotranspiration and changing seasonality of precipitation. In the Rhone valley of Switzerland, these conditions are triggering cascading effects leading to the dieback of Scots pine (Pinus sylvestris L.) trees, which dominate the forest stands in the driest parts of the valley. In parallel to the widespread reductions in tree growth and increased mortality which have been documented, the impact of water limitation on the soil microbiome could have prominent effects on the cycling of carbon and nitrogen. In this project we assess how water limitation acts synergistically on the biological interplay between Scots pine trees and associated soil microbial communities, and consequently influences carbon and nitrogen dynamics over time.

Visible Scots pine dieback
Visible Scots pine dieback close to the town of Visp (Valais) in summer 2017. Picture taken by Emily Solly.

Experimental set-up

A greenhouse experiment with 18 mesocosms consisting of small-scale Scots pine-soil-systems has been established at the ETH greenhouse facility in Eschikon in September 2019. These mesocosms are treated under controlled conditions with different amounts of irrigation to simulate three different soil moisture levels: Sufficient water supply (moist), decreased amount of water (dry) and water scarcity (very dry). State-of-the-art isotopic labeling techniques are used to trace alterations in the carbon and nitrogen transfer in the tree-soil-microbiome continuum due to drought. Investigations of changes in the soil microbiome and in the underlying functional metabolic potential related to drought are being done with molecular methods such as metabarcoding of ribosomal markers as well as shotgun metagenome sequencing. Measurements of plant growth and vitality as well as soil physicochemical properties are being performed in parallel.

Objectives

  1. To analyze the interactive responses of Scots pine trees and of the soil microbiome to drought and to detect how potential shifts in microbial   communities may affect tree vitality.
  2. To identify to which degree water shortage influences the microbial transformation of plant belowground carbon inputs.
  3. To determine how water shortage alters the mineralization of organic nitrogen and the uptake of nutrients by Scots pine trees.
Figure 2: Mesocosm experiment. Picture taken by Astrid Jäger.
Figure 2: Mesocosm experiment. Picture taken by Astrid Jäger.

Latest news

May 2020: Presentation of the project at external pageEGU-2020 General Assembly
September 2020: An isotopic labelling campaign with 13CO2 was conducted to trace the natural pathway of photosynthetic CO2 assimilates into roots, soil and microbes under experimental drought conditions.

Figure 3: Pulse labelling experiment. Pictures taken by Matti Barthel.
Figure 3: Pulse labelling experiment. Pictures taken by Matti Barthel.

Outcomes

This project aspires to be a major steppingstone in understanding the mechanistic interactions occurring between plants and soil microbial communities under water limitation. A main outcome will also be to constrain how these feedbacks influence the cycling of carbon and nitrogen in forest soils when trees die due to drought. We expect to provide a predictive framework of the dynamics related to water limitation leading to Scots pine mortality events.

Country: Switzerland

System: Scots pine forest system

Project duration: 2019 - 2023

Project partner: Arthur Gessler and Ivano Brunner, Swiss Federal Institute for Forest, Snow and Landscape research WSL, Switzerland; Timothy Eglinton, Department of Earth Sciences, ETH Zürich

Project funding: SNSF, Swiss National Science Foundation (pn: PZ00P2_180030)

Speech bubble Emily

For further information please contact Emily Solly (), Astrid Jäger (), Martin Hartmann () or Johan Six (). external pageLink to the project on research gate.

Speech bubble Astrid
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