Volatile chemicals from leaf litter are associated with invasiveness of a Neotropical weed in Asia

Abstract

Some invasive plant species appear to strongly suppress neighbors in their nonnative ranges but much less so in their native range. We found that in the field in its native range in Mexico, the presence of Ageratina adenophora, an aggressive Neotropical invader, was correlated with higher plant species richness than found in surrounding plant communities where this species was absent, suggesting facilitation. However, in two nonnative ranges, China and India, A. adenophora canopies were correlated with much lower species richness than the surrounding communities, suggesting inhibition. Volatile organic compound (VOC) signals may contribute to this striking biogeographical difference and the invasive success of A. adenophora. In controlled experiments volatiles from A. adenophora litter caused higher mortality of species native to India and China, but not of species native to Mexico. The effects of A. adenophora VOCs on seedling germination and growth did not differ between species from the native range and species from the nonnative ranges of the invader. Litter from A. adenophora plants from nonnative populations also produced VOCs that differed quantitatively in the concentrations of some chemicals than litter from native populations, but there were no chemicals unique to one region. Biogeographic differences in the concentrations of some volatile compounds between ranges suggest that A. adenophora may be experiencing selection on biochemical composition in its nonnative ranges.

Exotic Plant Invasion in the Context of Plant Defense against Herbivores

“…The NWH hypothesis predicts selection for higher production of chemical(s) novel for the invaded community (Supplemental Box S1; Callaway and Ridenour, 2004). In a common garden experiment, Inderjit et al (2011b) reported that leaf litter from exotic populations of A. adenophora from China and India had higher emissions of 2-carene and a-phellandrene and lower emission of (E)-b-caryophyllene (EbC), b-pinene, (E)-a-bergamotene, and bicyclogermacrene compared to native Mexican litter. They also found that the inhibition of native species in the presence of invasive A. adenophora litter could be due to the biogeographic variation in volatiles from exotic or native litter.…”

“…NWH assumes that an exotic plant produces higher amounts of chemicals in introduced ranges (Inderjit et al, 2006). An exotic plant, however, produces certain compounds in higher amounts in its native range too (see Inderjit et al, 2011b). Biogeographic variation in defense versus allelopathic chemicals might give better insights into NWH.…”

“…Since the distribution of A. adenophora has been restricted in Hawaii after the introduction of specialist herbivores, Mexican and Hawaiian populations of A. adenophora are likely to invest more in defense chemicals than Chinese or Indian populations. Chinese or Indian populations in the absence of specialist herbivores, however, should invest more in allelopathic VOCs as speculated by Inderjit et al (2011b). A common garden experiment with seeds from the native (Mexico) and nonnative (China, India, and Hawaii) ranges would help us to understand the pattern of VOC emission and their ecological roles-defense against herbivores vis-à-vis allelopathy.…”

“…Some terpenes such as EbC are present in high amounts in the native populations of A. adenophora compared to invasive populations (Inderjit et al, 2011b), which is reported to be involved in herbivore-induced plant defense (Rasmann et al, 2005;Degenhardt, 2009). Hiltpold et al (2011) reported that higher production of EbC in Zea mays roots upon herbivore attack by Diabrotica virgifera virgifera could be due to herbivoretriggered increase in the transcriptional activity of EbC synthase gene tps23.…”

“…Hiltpold et al (2011) reported that higher production of EbC in Zea mays roots upon herbivore attack by Diabrotica virgifera virgifera could be due to herbivoretriggered increase in the transcriptional activity of EbC synthase gene tps23. Biogeographic comparisons of herbivore damage, herbivore-induced proteins, qualitative, and quantitative variations in defense versus allelochemicals might help to explain biogeographic variation in chemicals and shift in resources from defense to growth in A. adenophora as observed by Feng et al (2009), Feng et al (2011), and Inderjit et al (2011b.…”