Experimental evidence of two mechanisms coupling leaf-level C assimilation to rhizosphere CO2 release

• Published in: Environmental and experimental botany Vol. 135; pp. 21 - 26
• Main Authors: Kayler, Zachary, Keitel, Claudia, Jansen, Kirstin, Gessler, Arthur
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.2017
• Subjects: Carbon isotope; Phloem transport; Pressure concentration wave; Rhizosphere; Soil respiration; Speed of link; Rhizosphere; Speed of link; Phloem transport; Soil respiration; Carbon isotope; Pressure concentration wave
• ISSN: 0098-8472; 1873-7307
• DOI: 10.1016/j.envexpbot.2016.12.002

•The time to which newly fixed carbon is transferred belowground is important.•We performed 13C labeling experiments designed to observe potential mechanisms.•Belowground respiration increased rapidly with the onset of photosynthesis.•Plants use at least two mechanisms to couple the plant-soil carbon continuum. The time span needed for carbon fixed by plants to induce belowground responses of root and rhizosphere microbial metabolic processing is of high importance for quantifying the coupling between plant canopy physiology and soil biogeochemistry, but recent observations of a rapid link cannot be explained by new assimilate transport by phloem mass flow alone. We performed 13CO2 labeling experiments designed to test if belowground respiration response to photosynthesis is faster than the arrival of new assimilates and to shed light on potential mechanisms. We provide experimental evidence that at least two mechanisms are employed by plants to couple rhizosphere respiration to canopy assimilation. We observed a fast increase of belowground respiration with the onset of photosynthesis, which we assume is induced by pressure concentration waves travelling through the phloem. A second, much later occurring, peak in respiration is fueled by new assimilates labeled with 13C. Plants and the rhizosphere are thus more tightly coupled than previously thought. Ultimately, the addition of a faster assimilate delivery mechanism to our conceptual framework of ecosystem dynamics will lead to a better understanding of belowground carbon and nutrient cycling and subsequent ecosystem response to disturbance and environmental stress.