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Silicon‐induced root nodulation and synthesis of essential amino acids in a legume is associated with higher herbivore abundance
Author(s) -
Johnson Scott N.,
Hartley Susan E.,
Ryalls James M. W.,
Frew Adam,
DeGabriel Jane L.,
Duncan Michael,
Gherlenda Andrew N.
Publication year - 2017
Publication title -
functional ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.272
H-Index - 154
eISSN - 1365-2435
pISSN - 0269-8463
DOI - 10.1111/1365-2435.12893
Subject(s) - biology , herbivore , shoot , legume , pisum , silicon , acyrthosiphon pisum , medicago sativa , botany , root nodule , agronomy , symbiosis , bacteria , aphididae , chemistry , pest analysis , homoptera , genetics , organic chemistry
Summary 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. A lay summary is available for this article.