Abstract
One of the most remarkable metabolic features of plant roots is their ability to secrete a wide range of compounds into the rhizosphere, defined as the volume of soil around living roots. Around 5%-21% of total photosynthetically fixed carbon is transferred into the rhizosphere through root exudates. Until recently, studies on the quantity and quality of root exudates were conducted mostly under axenic or monoxenic in vitro conditions. Today, in situ assays are required to provide a better understanding of root exudates dynamics and role in plant-microbe interactions. By incubating plants with 13CO2 in situ for one week and quantifying 13C enrichment from the root-adhering soil using mass spectrometry, we were able to determine root exudate levels. Indeed, labeled substrate 13CO2 is converted into organic carbon via plant photosynthesis and transferred into the soil through root exudation. We assume that all 13C increases above natural abundance are mainly derived from exudates produced by 13C-labeled plants.
Keywords: Root exudates, Plant, Rhizosphere, 13CO2 labeling, Root-adhering soil, 13C-content, Isotope Ratio Mass Spectrometry, Poaceae, Monocotyledon, Legume, Arabidopsis thaliana
Background
Through the exudation of a wide variety of compounds, plants communicate with the soil microbial community in their immediate vicinity, cope with herbivores, foster beneficial symbioses, change the chemical and physical properties of the soil, and inhibit the growth of competing plant species. Understanding how plants differ quantitatively in their root exudate patterns, according to their genotypes and traits as well as to environmental parameters and the soil microbial community is an exciting research challenge. This objective could be achieved by quantifying root exudate content using 13CO2 plant-labeling coupled with a 13C enrichment measurement from the root-adhering soil using mass spectrometry. This protocol was set up by using different plant species such as Poaceae, legumes (Medicago truncatula), Arabidopsis thaliana, and Monocotyledon plants such as maize and wheat. As rhizodeposition also depends on plant species, the collection period was after 10 weeks for Poaceae and 4 weeks for the rest. This method can be used with other species, for which the collection period must be set up according to what is known about the studied plant.
Materials and Reagents
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Data analysis
Acknowledgments
The method to measure root exudate content was developed in the Microbial Ecology laboratory jointly with Dr. L. Simon and published by Guyonnet et al. (2018a) Ecology and Evolution DOI: 10.1002/ece.3.4383. We thank the “Serre et chambres climatiques” platform (Université Lyon1, FR BioEnviS) for growing the plants, as well as the “Ecologie Isotopique” platform (Université Lyon 1, UMR 5023) for elemental and isotopic analysis. This work was supported by the French National Research Agency (ANR-18-CE32-0005, DIORE).
Competing interests
No competing interests to declare.
References
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