Mary Beyer's Master thesis was awarded with the Prize for the Best Plant Science Master Thesis, which was carried out at Salzburg University in the year 2019.
Is heavy metal hyperaccumulation in Noccaea caerulescens acting as a defence mechanism against herbivores?
Mary Beyer found out that accumulated heavy metals can have a deterring effect on herbivores, supporting the “elemental defence hypothesis”. However, the degree of this effect depends largely on the type of heavy metal and the species of herbivore as the feeding experiments showed.
The aim of this thesis was to provide new insights to the “elemental defence hypothesis”. According to this hypothesis, heavy metals act as a defence mechanism, by deterring or killing herbivores and pathogens, which led to a higher accumulation in certain plants (hyperaccumulators). Four types of herbivores (Arion vulgaris, Vanessa cardui, Plutella xylostella and Pieris rapae) were offered plants of the hyperaccumulator Noccaea caerulescens, treated with different concentrations of nickel and zinc, in a free choice feeding trial. The feeding damage on each plant was determined and thus it was assessed if nickel and/or zinc had any effect on the herbivores feeding behaviour.
The results support a significant correlation of feeding preferences and foliar zinc concentrations, reducing herbivory by up to 20%. However, this was not the case for foliar nickel concentrations, though a tendency of some herbivores preferring low levels of nickel could be observed. This shows that the effect of accumulated heavy metals on herbivory depends largely on the type of metal and species of herbivore.
Mary Beyer conducted this work at the institute for ecology and evolution at Salzburg University in the working group of Prof. Hans-Peter Comes.