Nutrient enrichment promotes invasion success of alien plants via increased growth and suppression of chemical defenses

Abstract

In support of the prediction of the enemy release hypothesis regarding a growth–defense trade‐off, invasive alien plants often exhibit greater growth and lower anti‐herbivory defenses than native plants. However, it remains unclear how nutrient enrichment of invaded habitats may influence competitive interactions between invasive alien and co‐occurring native plants, as well as production of anti‐herbivore defense compounds, growth‐promoting hormones, and defense‐regulating hormones by the two groups of plants. Here, we tested whether: (i) nutrient enrichment causes invasive alien plants to produce greater biomass and lower concentrations of the defense compounds flavonoids and tannins than native plants; and (ii) invasive alien plants produce lower concentrations of a defense‐regulating hormone jasmonic acid (JA) and higher concentrations of a growth‐promoting hormone gibberellic acid (GA3). In a greenhouse experiment, we grew five congeneric pairs of invasive alien and native plant species under two levels each of nutrient enrichment (low vs. high), simulated herbivory (leaf clipping vs. no‐clipping), and competition (alone vs. competition) in 2.5‐L pots. In the absence of competition, high‐nutrient treatment induced a greater increase in total biomass of invasive alien species than that of native species, whereas the reverse was true under competition as native species benefitted more from nutrient enrichment than invasive alien species. Moreover, high‐nutrient treatment caused a greater increase in total biomass of invasive alien species than that of native species in the presence of simulated herbivory. Competition induced higher production of flavonoids and tannins. Simulated herbivory induced higher flavonoid expression in invasive alien plants under low‐nutrient than high‐nutrient treatments. However, flavonoid concentrations of native plants did not change under nutrient enrichment and simulated herbivory treatments. Invasive alien plants produced higher concentrations of GA3 than native plants. Taken together, these results suggest that impact of nutrient enrichment on growth of invasive alien and co‐occurring native plants may depend on the level of competition that they experience. Moreover, invasive alien plants might adjust their flavonoid‐based defense more efficiently than native plants in response to variation in soil nutrient availability and herbivory pressure. Our findings suggest that large‐scale efforts to reduce nutrient enrichment of invaded habitats may help to control future invasiveness of target alien plant species.

Artificial night‐time lighting and nutrient enrichment synergistically favour the growth of alien ornamental plant species over co‐occurring native plants

“…Several studies have found empirical support for this prediction (Magaña-Hernández et al, 2020;Mokany et al, 2006;Oduor, 2022;Shan et al, 2022;Xue et al, 2023). The present results also support the prediction of the optimal partitioning theory.…”

Root plasticity benefits a global invasive species in eutrophic coastal wetlands

“…Moreover, under herbivory pressure, native plant species should maintain a stable anti-herbivore defence with low trait plasticity in response to variation in soil nutrient availability (Dawson et al, 2004;Shan et al, 2022). In other words, for native species F I G U R E 8 Relationships between above-ground biomass (AGB) and principal component analysis axis one (PC1) for root traits of Phragmites australis (a) and Spartina alterniflora (b).…”

“…For example, salt pressure was found to constrain the growth plasticity of native P. australis in response to N heterogeneity (Guan et al., 2021). Moreover, under herbivory pressure, native plant species should maintain a stable anti‐herbivore defence with low trait plasticity in response to variation in soil nutrient availability (Dawson et al., 2004; Shan et al., 2022). In other words, for native species under changing environmental conditions, plasticity is not always advantageous, as plastic adaptive responses to a given environmental factor can turn out to be maladaptive when another factor is stressful (Valladares et al., 2007).…”

Perspectives of invasive alien species management in China

“…The enemy release hypothesis suggests that invasive alien plants, due to a growth–defense trade‐off, often demonstrate superior growth and weaker antiherbivory defenses compared with native plants. Shan et al (2023) conducted a multispecies greenhouse experiment to examine how nutrient enrichment in invaded habitats influenced this growth–defense trade‐off between invasive and co‐occurring native plants. Their study revealed that invasive species, relative to native ones, displayed an enhanced ability to adjust their flavonoid‐based defenses in response to shifts in soil nutrient availability and herbivory pressure.…”