Comparing the Above and Below-Ground Chemical Defences of Three Rumex Species Between Their Native and Introduced Provenances

Abstract

Compared to their native range, non-native plants often experience reduced levels of herbivory in the introduced range. This may result in reduced pressure to produce chemical defences that act against herbivores. We measured the most abundant secondary metabolites found in Rumex spp., namely oxalates, phenols and tannins. To test this hypothesis, we compared native (UK) and introduced (NZ) provenances of three different Rumex species (R. obtusifolius, R. crispus and R. conglomeratus, Polygonaceae) to assess whether any significant differences existed in their levels of chemical defences in either leaves and roots. All three species have previously been shown to support a lower diversity of insect herbivores and experience less herbivory in the introduced range. We further examined leaf herbivory on plants from both provenances when grown together in a common garden experiment in New Zealand to test whether any differences in damage might be consistent with variation in the quantity of chemical defences. We found that two Rumex species (R. obtusifolius and R. crispus) showed no evidence for a reduction in chemical defences, while a third (R. conglomeratus) showed only limited evidence. The common garden experiment revealed that the leaves analysed had low levels of herbivory (~ 0.5%) with no differences in damage between provenances for any of the three study species. Roots tended to have a higher concentration of tannins than shoots, but again showed no difference between the provenances. As such, the findings of this study provide no evidence for lower plant investments in chemical defences, suggesting that other factors explain the success of Rumex spp. in New Zealand.

Keywords: Alien species; Chemical defences; Introduced; Native; Plant invasion; Weeds.

Fig. 1

Leaf soluble (a), total (b) and percent soluble (c) oxalic acid content of Rumex spp. grown from seeds from the native (United Kingdom, UK) or introduced (New Zealand, NZ) ranges under greenhouse conditions. For each species, 16 replicates per provenance (UK and NZ) were averaged. Error bars ± 1SE

Fig. 2

Leaf and roof total phenols (a & b), ellagitannins (c & d) and percentage of ellagitannins (e & f) out of total phenols of Rumex spp. grown from seeds from the native (United Kingdom, UK) or introduced (New Zealand, NZ) ranges under controlled greenhouse conditions expressed in GAE (Gallic Acid Equivalent). For each species, 16 replicates per provenance (UK and NZ) were averaged. Error bars ± 1SE

Fig. 3

Total leaf (a) and root (b) tannin content of Rumex spp. grown from seeds from the native (United Kingdom, UK) or introduced (New Zealand, NZ) ranges under controlled greenhouse conditions. For each species, 16 replicates per provenance (UK and NZ) were averaged. Error bars ± 1SE

Fig. 4

Percentage leaf area damaged by herbivores of plants from the native (UK) and introduced (NZ) provenance when grown together  in common garden experiments in New Zealand. Error bars ± 1SE