Direct evidence for modulation of photosynthesis by an arbuscular mycorrhiza‐induced carbon sink strength

Abstract

Summary It has been suggested that plant carbon (C) use by symbiotic arbuscular mycorrhizal fungi (AMF) may be compensated by higher photosynthetic rates because fungal metabolism creates a strong C sink that prevents photosynthate accumulation and downregulation of photosynthesis. This mechanism remains largely unexplored and lacks experimental evidence. We report here two experiments showing that the experimental manipulation of the mycorrhizal C sink significantly affected the photosynthetic rates of cucumber host plants. We expected that a sudden reduction in sink strength would cause a significant reduction in photosynthetic rates, at least temporarily. Excision of part of the extraradical mycorrhizal mycelium from roots, and causing no disturbance to the plant, induced a sustained (10–40%) decline in photosynthetic rates that lasted from 30 min to several hours in plants that were well‐nourished and hydrated, and in the absence of growth or photosynthesis promotion by mycorrhizal inoculation. This effect was though minor in plants growing at high (700 ppm) atmospheric CO2. This is the first direct experimental evidence for the C sink strength effects exerted by arbuscular mycorrhizal symbionts on plant photosynthesis. It encourages further experimentation on mycorrhizal source–sink relations, and may have strong implications in large‐scale assessments and modelling of plant photosynthesis.

Carbon for nutrient exchange between arbuscular mycorrhizal fungi and wheat varies according to cultivar and changes in atmospheric carbon dioxide concentration

“…The extent to which increasing atmospheric [CO 2 ] will impact crop-AMF associations remains unclear (Cotton, 2018 (Alberton, Kuyper, & Gorissen, 2005;Drigo et al, 2013;Field et al, 2012;Treseder, 2004). Furthermore, recent evidence even suggests that AMF carbon acquisition from host plants might directly increase rates of carbon fixation (Gavito, Jakobsen, Mikkelsen, & Mora, 2019), potentially by ameliorating end-product inhibition of photosynthesis (Arp, 1991). Greater C acquisition by AMF may enable further hyphal proliferation through soil and thus increase their assimilation of mineral nutrients and subsequently increase transfer to host plants.…”

The Influence of No-till Farming on Durum Wheat Mycorrhization in a Semi-Arid Region: A Long-Term Field Experiment

“…AMF are obligate biotrophs and constitute a strong sink for plant carbon (Gavito et al, 2019) they take advantage of 3% to 20% of the carbon substances produced by the host plant (Strullu et al, 1991;Smith & Read, 2008;Garbaye, 2013). These reserves stored in the vesicles will allow the AMF to develop extended extraradical hyphal networks for efficient soil exploration (Keymer et al, 2017).…”

Carbon investment into mobilization of mineral and organic phosphorus by arbuscular mycorrhiza

“…The PLFA and NLFA samples were exposed to mild alkaline methanolysis. Transformation of phospholipids and neutral lipids into free fatty acid methyl esters (FAMEs) was based on Frostegård et al (1991) with modifications by Bischoff et al (2016). FAMEs were separated by gas chromatography using an Agilent 7890A GC system (Agilent Technologies Ireland Ltd., Cork, Ireland) equipped with a 60m Zebron capillary GC column (0.25-mm diameter and 0.25-μm film thickness; Phenomenex, Torrance, California, USA) and quantified with a flame ionization detector, using He as carrier gas.…”

“…Photosynthetic rates are often higher in mycorrhizal than in non-mycorrhizal plants (Augé et al 2016), as a result of improved plant nutrition, especially of Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00374-020-01505-5) contains supplementary material, which is available to authorized users. P, in mycorrhizal plants (Gavito et al 2019). The AM plants allocate 4-20% of the total C fixed into the AMF structures (Parniske 2008), and up to 5% of net photosynthesis is lost by hyphal respiration (Moyano et al 2007).…”