Abstract
Secondary compounds can contribute to the success of non‐native plant species if they reduce damage by native herbivores or inhibit the growth of native plant competitors. However, there is opposing evidence on whether the secondary compounds of non‐native plant species are stronger than those of natives. This may be explained by other factors, besides plant origin, that affect the potential of plant secondary compounds. We tested how plant origin, phylogeny, growth strategy and stoichiometry affected the allelopathic potential of 34 aquatic plants. The allelopathic potential was quantified using bioassays with the cyanobacterium Dolichospermum flos‐aquae. The allelopathic potential showed a strong phylogenetic signal, but was similar for native and non‐native species. Growth strategy was important, and emergent plants had twice the allelopathic potential as compared to submerged plants. Furthermore, the allelopathic potential was positively correlated to the foliar carbon‐to‐phosphorus (C:P) and total phenolic content. We conclude that eudicot plant species with an emergent growth strategy and high plant C:P ratio exhibit a high allelopathic potential. Unless non‐native plant species match this profile, they generally have a similar allelopathic potential as natives.
Highlights
Plants contain secondary compounds that improve plant fitness in various ways, for instance by reducing the growth of competitors through allelopathy (Mulderij et al 2007, Hilt and Gross 2008, Aschehoug et al 2014), by repelling herbivores (Callaway and Ridenour 2004, Dorenbosch and Bakker 2011, Fornoff and Gross 2014), resisting pathogens (Harborne 1977, Lattanzio et al 2006) and interfering with decomposition (Horner et al 1988, Bardon et al 2014, Suseela et al 2015, McLeod et al 2016)
Growth strategy and plant origin significantly affected the allelopathic potential when tested together in a three-way ANOVA: plant phylogeny explained most variation in allelopathic potential (F1,24 = 12.8; P = 0.002), plant growth strategy explained slightly less variation (F1,24 = 9.3; P = 0.005) and plant origin explained least of the variation (F1,24 = 8.4; P = 0.008)
Separate t-tests showed that eudicots exhibited a higher allelopathic potential than monocots (Fig. 2A, t16.2 = 3.3; P = 0.005), whereas there was no effect of plant origin: native and non-native plant species had a similar mean allelopathic potential (Fig. 2B, t31.1 = 0.60; P = 0.56)
Summary
Plants contain secondary compounds that improve plant fitness in various ways, for instance by reducing the growth of competitors through allelopathy (Mulderij et al 2007, Hilt and Gross 2008, Aschehoug et al 2014), by repelling herbivores (Callaway and Ridenour 2004, Dorenbosch and Bakker 2011, Fornoff and Gross 2014), resisting pathogens (Harborne 1977, Lattanzio et al 2006) and interfering with decomposition (Horner et al 1988, Bardon et al 2014, Suseela et al 2015, McLeod et al 2016). Secondary compounds contribute to the success of exotic plant species, because many exotic plants possess secondary compounds that are novel to the native community (reviewed in Callaway and Ridenour 2004, Cappuccino and Carpenter 2005, Macel et al 2014) These novel compounds are known to be bioactive (Cappuccino and Arnason 2006), and may deter native herbivores (Macel et al 2014) or inhibit the growth of native plants (Ridenour and Callaway 2001, Svensson et al 2013), improving the fitness of non-native plants, which can provide a competitive advantage over native plant species (Callaway and Ridenour 2004, Kim and Lee 2011). These contrasting results may be due to natural inter- and intraspecific variation in secondary compound composition and levels, which are determined by multiple factors, including, but not limited to, plant phylogeny, plant growth strategy and elemental composition
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