'mutualism' in Plant-Microbe Symbiosis

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From onlinelibrary.wiley.com - November 24, 2017 11:48 AM

Abstract: The symbiosis between plants and root-colonizing arbuscular mycorrhizal (AM) fungi is one of the most ecologically important examples of interspecific cooperation in the world. AM fungi provide benefits to plants; in return plants allocate carbon resources to fungi, preferentially allocating more resources to higher-quality fungi. However, preferential allocations from plants to symbionts may vary with environmental context, particularly when resource availability affects the relative value of symbiotic services. We ask how differences in atmospheric CO2-levels influence root colonization dynamics between AMF species that differ in their quality as symbiotic partners. We find that with increasing CO2-conditions and over multiple plant generations, the more beneficial fungal species is able to achieve a relatively higher abundance. This suggests that increasing atmospheric carbon supply enables plants to more effectively allocate carbon to higher-quality mutualists, and over time helps reduce lower-quality AM abundance. Our results illustrate how environmental context may affect the extent to which organisms structure interactions with their mutualistic partners and have potential implications for mutualism stability and persistence under global change.

Keywords: context-dependence global change mutualism rewards sanction

From link.springer.com - July 24, 2017 5:30 AM

Background and aims

Arbuscular mycorrhizal fungi (AMF) are plant root symbionts highly specialized upon phosphorus (P) supply to their hosts. We investigated plants’ ability to regulate carbon (C) flow to AMF depending on the soil P supply.

Methods

Leek (Allium porrum), medic (Medicago truncatula), and ryegrass (Lolium perenne) were subjected to AMF inoculation and/or P fertilization in a glasshouse experiment. The C flows were traced using 13C pulse labelling.

Results

Mycorrhizal P uptake responses were lowered by P fertilization in all tested plant species. Independently from the C flow to the roots, the C flow to AMF-signature fatty acid 16:1ω5 were reduced by P fertilization in leek and ryegrass (but not in medic). Calculated mycorrhizal C costs ranged between 0.9% and 10.5% of the plant C budget.

Conclusions

Suppression of the C flow from the plants to AMF resulted from both reduced abundance of AMF in the roots and lowered relative C income per unit of AMF biomass in P-fertilized pots. Although inconsistencies amongst different plant species demand caution in making generalizations, these results suggest an active role of host plants in regulating the C flow to AMF.

Keywords: Arbuscular mycorrhiza Carbon allocation Mycorrhizal cost Symbiotic benefits Biological market theory Phosphorus fertilization

Plant-Microbe Symbiosis

Tracking plant preference for higher-quality mycorrhizal symbionts under varying CO2 conditions over multiple generations.

Carbon flow from plant to arbuscular mycorrhizal fungi is reduced under phosphorus fertilization. Plant and Soil