Arbuscular Mycorrhizal Symbiosis with Arundo donax Decreases Root Respiration and Increases Both Photosynthesis and Plant Biomass Accumulation

The effect of arbuscular mycorrhiza (AM) symbiosis on plant growth is associated with the balance between costs and benefits. A feedback regulation loop has been described in which the higher carbohydrate cost to plants for AM symbiosis is compensated by increases in their photosynthetic rates. Nevertheless, plant carbon balance depends both on photosynthetic carbon uptake and respiratory carbon consumption. The hypothesis behind this research was that the role of respiration in plant growth under AM symbiosis may be as important as that of photosynthesis. This hypothesis was tested in Arundo donax L. plantlets inoculated with Rhizophagus irregularis and Funneliformis mosseae. We tested the effects of AM inoculation on both photosynthetic capacity and in vivo leaf and root respiration. Additionally, analyses of the primary metabolism and ion content were performed in both leaves and roots. AM inoculation increased photosynthesis through increased CO2 diffusion and electron transport in the chloroplast. Moreover, respiration decreased only in AM roots via the cytochrome oxidase pathway (COP) as measured by the oxygen isotope technique. This decline in the COP can be related to the reduced respiratory metabolism and substrates (sugars and tricarboxylic acid cycle intermediates) observed in roots. Manuscript ID PCE‐16‐1037 ‘Arbuscular mycorrhizal symbiosis with Arundo donax decreases root respiration and increases both photosynthesis and plant biomass accumulation’: This research allows elucidation a bit more the ‘black‐box’ about AMF mechanisms that orchestrate plant responses, using gas exchange but also the in vivo electron partitioning technique, suggested as a new tool to study the respiratory behaviour of root–fungus matrix. Arbuscular mycorrhiza (AM) symbiosis decreases plant respiration and increases net photosynthesis, but also affects plant metabolism of Arundo donax plantlets, enhancing plant biomass accumulation.