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INPLAMINT Subproject H

Richard van Duijnen und Prof. Vicky Temperton
Institute of Ecology
Leuphana University Lüneburg

Leuphana Universität Lüneburg

Studying the buffering role of soil microbes and the role of plant root architecture as a modulator: Using high carbon substrates added to soils after crop harvest, we aim to immobilize left-over nitrogen in the soil (mainly from decomposing plant material), which the new crop cannot always fully take up before winter. We then aim to understand whether one can harness these nutrients for the plant when they are released by the microbes next spring.
Our subproject focuses on plant-microbe competition for nutrients and how this affects plant traits, especially roots under controlled conditions in the greenhouse and climate chamber. We also study the role of facilitation and mutualisms such as those found in mycorrhizal and rhizobial plant species on competition for nutrients. Our experiments are linked to the agricultural field experiment with INPLAMINT partners at the Christian-Albrecht University in Kiel as well as controlled experiments at the Universität Köln and Forschungszentrum Jülich.
Our focal crop species is barley (both summer and winter varieties) and we focus on root architecture as well as the rhizosphere (the area of soil adjacent to roots), where plants interact directly with microbes with major implications for plant performance as well as nutrient availability.

Main scientific questions:

  • Visualizing and quantifying how different amounts and timing of nutrient addition (N,P) affect plant traits, particularly root system architecture (Stoichiometry and Timing Rhizobox Experiments, Fig. 1)
  • What happens during a crop rotation (faba bean/spring canola/spring barley/white lupine followed by winter barley) in terms of nitrate leaching when one adds different high C substrates after harvest of the first crops? (Crop Rotation Experiment, Fig. 2)
  • The role of plant functional group (rhizobial/non; arbuscular mycorrhizal/non) within pre-crops for the subsequent crop and soil microbiome. (Crop Rotation Experiment, Fig.2)

Overview of Experiments:
Timing and Amount of Nutrient Addition with Barley (Rhizobox Experiments)
Using rhizoboxes with see-through plexiglas sheets on one side, we can visualize root growth dynamically by photographing the root system at regular intervals (Fig.1). One experiment tests the effect of adding different nutrient stoichiometries on root performance, using different planting densities to mimic seeding densities and plant competition found in agricultural settings. Using planar optodes to measure pH of the rhizosphere dynamically we aim to start to understand how the treatments affect plant physiological processes of relevance for root exudation and nutrient availability. A second experiment aims to understand how the timing of addition of N and P as nutrients affects root performance within these settings.

Roots visible growing Fig 1. Roots visible growing along a glass plate in a rhizotron.

Crop rotation using four different plant functional groups as pre-crops before winter barley (Mesocosm Experiment outside)
Simulating the crop rotation in the Kiel field experiment we set up a large experiment outdoors in 2016, with four different plant functional groups as well as two carbon amendments and two fertilizer levels provided to the focal plant winter barley. Plants are either mycorrhizal or not, or rhizobial or not (allowing them to fix atmospheric N) in all possible combinations: barley and canola, fava bean and lupine). We are measuring nitrate in leachate obtained from pots with fava bean and barley as pre-crops (see Fig.2) and will link our data with the leachate measurement and modeling at Christian-Albrecht University in Kiel. In collaboration with microbiologists at the Freie Universität Berlin (http://www.bcp.fuberlin.de/en/biologie/arbeitsgruppen/botanik/ag_rillig/index.html) and Helmholz Zentrum München (https://www.helmholtz-muenchen.de/comi/index.html) we aim to understand whether microbes such as mycorrhizae and rhizobia can survive a crop sequence where non-mycorrhizal and non-rhizobial species were present, as well as seeing which microbes are present and active in relation to different pre-crop species, C amendment and nutrient treatments.

Mesocosm experiment Fig 2. Mesocosm experiment in August 2016. In front is the setup to collect the leachate, in the back spring canola and white lupine are still growing.


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