These soil fungi, called arbuscular mycorrhizal fungi (AMF), are found in virtually all terrestrial ecosystems, and they form symbiotic relationships with a wide variety of plants.
The plants supply sugars produced by photosynthesis to the fungal partner, and the fungi, by effectively increasing the surface area of the plant roots, may facilitate water and mineral uptake by the plants.
In other words, the plants invest sugar resources to feed their fungal partners, and the fungi provide a return on this investment in the form of water and minerals, in particular phosphorus and nitrogen, which are quite valuable to most plants.
What’s very interesting is that neighboring plants, even different species, can be connected to a mutual fungal network, known as a common mycorrhizal network (CMN).
Moreover, one CMN can also be connected to other CMNs. Thus, the possibilities regarding potential inter-plant communication and resource sharing are quite intriguing, but very poorly understood.
A paper recently published in the journal Plant Physiology (see Ref. 1 below) has provided new insights about how neighboring plants may benefit from these CMNs.
Briefly, what they found was that some plant species may invest relatively little in the CMN but benefit greatly, and other plant species may invest a lot but get back not so much. For example, see the figure below.
“Terms of trade in CMNs between flax and sorghum formed by G. intraradices and G. mosseae. In this scheme, the carbon investment of the plants is depicted by green arrows. In both CMNs, sorghum invested more than twice as much than flax in terms of carbon. The return, in the form of the nutrients phosphorus (P) and nitrogen (N), is illustrated by the yellow and orange arrows, respectively. In the CMN formed by G. intraradices, the return was extremely uneven; flax obtained 80% to 94% of the nutrients delivered by the CMN, and sorghum, the main investor, obtained only 6% to 20%. In the CMN formed by G. mosseae, both flax and sorghum received an approximately equal share of the nutrients delivered by the CMN, but because flax invested less than half as much carbon compared with sorghum, it still benefited from its neighbor.” (Figure 6 and figure legend are from Ref. 1 below)
Companion planting (a.k.a., inter-cropping or mixed-culture cropping) is the practice of planting of different crops in proximity (in gardening and agriculture). A form of polyculture, it’s based on the theory that “companion plant species” assist each other in nutrient uptake, pest control, pollination, and other factors necessary to increasing crop productivity.
(By the way, a good introduction to companion planting for gardeners is: Carrots Love Tomatoes: Secrets of Companion Planting for Successful Gardening)
What perhaps are the most important implications of the findings reported in the paper by Walder, et al. (Ref. 1 below) have to do with this subject of inter-cropping, that is, growing two or more crop plant species together, such as cereal-legume cropping systems. Think corn plants growing amongst bean plants.
Such mixed-culture cropping systems are often more efficient and more productive than mono-cropping systems. There’ve been many explanations for this, such as legumes (which fix nitrogen from the air) providing nitrogen to the corn.
But this paper suggests an additional explanation. That is, “… CMNs may contribute to interplant facilitation and the productivity boosts often found with intercropping compared with conventional monocropping.” (from Ref. 1 below)
Bottom Line: To satisfy the ever increasing global demand for food, inter-cropping systems, facilitated by CMNs, may help boost agricultural productivity in a sustainable way.
1. Walder, F., H. Niemann, M. Natarajan, M. F. Lehmann, T. Boller and A. Wiemken (2012) “Mycorrhizal networks: common goods of plants shared under unequal terms of trade.” Plant Physiology, Vol. 159, pp. 789-797. (FullText)*
*Thanks to the journal Plant Physiology for making this an open access paper.
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