Silicon‐induced root nodulation and synthesis of essential amino acids in a legume is associated with higher herbivore abundance

Johnson, Scott N. and Hartley, Susan E. and Ryalls, James M. W. and Frew, Adam and DeGabriel, Jane L. and Duncan, Michael and Gherlenda, Andrew G. (2017) Silicon‐induced root nodulation and synthesis of essential amino acids in a legume is associated with higher herbivore abundance. Functional Ecology, 31 (10). pp. 1903-1909. ISSN 0269-8463


Ecologists have become increasingly aware that silicon uptake by plants, especially the Poaceae, can have beneficial effects on both plant growth and herbivore defence. The effects of silicon on other plant functional groups, such as nitrogen-fixing legumes, have been less well studied. Silicon could, however, indirectly promote herbivore performance in this group if reported increases in N-2 fixation caused improvements in host plant quality for herbivores.

We tested how silicon supplementation in the legume (Medicago sativa) affected plant growth rates, root nodulation and foliage quality (silicon content and amino acid profiles) for an insect herbivore (Acyrthosiphon pisum).

Plants supplemented with silicon (Si+) grew three times as quickly as those without supplementation (Si-), almost entirely in shoot mass. While root growth was unaffected by silicon uptake, root nodules containing nitrogen-fixing bacteria were 44% more abundant on Si+ plants. Aphid abundance was twice as high on Si+ plants compared to Si- plants and was positively correlated with silicon-stimulated plant growth.

Si+ plants accumulated more than twice as much silicon as Si- plants, but did not have higher silicon concentrations because of dilution effects linked to the rapid growth of Si+ plants. Si+ plants showed a 65% increase in synthesis of essential foliar amino acids, probably due to increased levels of root nodulation.

These results suggest that increased silicon supply makes M. sativa more susceptible to A. pisum, mainly because of increased plant growth and resource availability (i.e. essential amino acids). While silicon augmentation of the Poaceae frequently improves herbivore defence, the current study illustrates that this cannot be assumed for other plant families where the beneficial effects of silicon on plant growth and nutrition may promote herbivore performance in some instances.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Permanent restricted access to Published version, in accordance with the copyright policy of the publisher.
Faculty/School / Institute/Centre: No Faculty
Faculty/School / Institute/Centre: No Faculty
Date Deposited: 20 Nov 2019 06:19
Last Modified: 21 Nov 2019 04:33
Uncontrolled Keywords: amino acids, aphids, legume, nitrogen fixation, nodulation plant defence, silica, silicon
Fields of Research (2008): 05 Environmental Sciences > 0501 Ecological Applications > 050199 Ecological Applications not elsewhere classified
05 Environmental Sciences > 0503 Soil Sciences > 050303 Soil Biology
06 Biological Sciences > 0607 Plant Biology > 060799 Plant Biology not elsewhere classified
Socio-Economic Objectives (2008): D Environment > 96 Environment > 9604 Control of Pests, Diseases and Exotic Species > 960499 Control of Pests, Diseases and Exotic Species not elsewhere classified
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