Below ground crop/weed interaction

Reducing herbicide use is an important social and environmental goal, as concern is growing about the development of herbicide-resistant weeds and the ecological consequences of herbicide application. Several cover crops are known to successfully suppress weeds, providing a pertinent answer to this problem. However, in order to use cover crops adequately, the mechanisms of weed suppression need to be elucidated and understood. Besides direct resource competition, growth repression through root interactions can play a decisive role. However, so far rhizosphere interactions of two neighboring plants have received little attention in the scientific community. In previous experiments we could demonstrate that below ground interactions between the cover crops Fagopyrum esculentum (buckwheat) and Avena strigosa (black oat) led to growth suppression of Amaranthus retroflexus (redroot pigweed), presumably induced by specific cover crop root exudates. Based on these findings, we aim to further investigate cover crop root exudates and to identify putative growth suppressive compounds. We will test six research hypotheses: (H1) The selected cover crops can recognize the presence of heterospecific neighbors via interacting root systems, which leads to a systemic modification of cover crop root exudation. (H2) Certain compound groups and/or specific molecules respond to a species-specific recognition, while others respond more generally to the presence of another plant. (H3) Certain compound groups and/or specific molecules from cover crop root exudates are responsible for growth suppressive effects. (H4) Growth suppressive effects are reflected by transcriptome changes of Arabidopsis thaliana (thale cress) and Brachypodium distachyum (stiff brome). (H5) Arabidopsis thaliana and Brachypodium distachyum root exudation is altered by the presence of different cover crops. (H6) Putative compounds responsible for growth repression can be detected in agricultural soil. Our methodological approach employs a validated split-root set-up enabling differential root exudate collection and analysis. First experiments will be performed in undisturbed soil-free glass bead cultures. Differential chemical analysis of the collected exudates will follow an already implemented workflow utilizing accurate mass spectrometry in combination with fit-for-purpose separation methods. Identity confirmation of significant compounds will make use of dedicated accurate mass databases including information on fragment spectra. Subsequently, root exudates will be collected from soil grown roots and rhizosphere soil solution to confirm their presence in soil. Moreover, phenotypic and transcriptomic changes induced by direct interaction of roots and the impact of selected compounds will be studied in Arabidopsis thaliana and Brachypodium distachyum. The results of the studies will provide novel insights in belowground plant-plant interactions and provide information for the development and use of weed suppressive cover crops, as a step towards new cultural control strategies for integrated weed management.