title: High tolerance to salinity and herbivory stresses may explain the expansion of Ipomoea cairica to salt marshes.
abstract: BACKGROUND
  Invasive plants are often confronted with heterogeneous environments and various stress factors during their secondary phase of invasion into more stressful habitats. A high tolerance to stress factors may allow exotics to successfully invade stressful environments. Ipomoea cairica, a vigorous invader in South China, has recently been expanding into salt marshes.
  
  
  RESULTS
  To examine why this liana species is able to invade a stressful saline environment, we utilized I. cairica and 3 non-invasive species for a greenhouse experiment. The plants were subjected to three levels of salinity (i.e., watered with 0, 4 and 8 g L(-1) NaCl solutions) and simulated herbivory (0, 25 and 50% of the leaf area excised) treatments. The relative growth rate (RGR) of I. cairica was significantly higher than the RGR of non-invasive species under both stress treatments. The growth performance of I. cairica was not significantly affected by either stress factor, while that of the non-invasive species was significantly inhibited. The leaf condensed tannin content was generally lower in I. cairica than in the non-invasive I. triloba and Paederia foetida. Ipomoea cairica exhibited a relatively low resistance to herbivory, however, its tolerance to stress factors was significantly higher than either of the non-invasive species.
  
  
  CONCLUSIONS
  This is the first study examining the expansion of I. cairica to salt marshes in its introduced range. Our results suggest that the high tolerance of I. cairica to key stress factors (e.g., salinity and herbivory) contributes to its invasion into salt marshes. For I. cairica, a trade-off in resource reallocation may allow increased resources to be allocated to tolerance and growth. This may contribute to a secondary invasion into stressful habitats. Finally, we suggest that I. cairica could spread further and successfully occupy salt marshes, and countermeasures based on herbivory could be ineffective for controlling this invasion.
authors.affiliation: State Key Laboratory of Biocontrol and Guangdong Key Laboratory of Plant Resources, School of Life Sciences, Sun Yat-Sen University, Guangzhou, China.
authors.forename: Gang
authors.initials: G
authors.lastname: Liu
authors.forename: Qiao-Qiao
authors.initials: QQ
authors.lastname: Huang
authors.forename: Zhen-Guang
authors.initials: ZG
authors.lastname: Lin
authors.forename: Fang-Fang
authors.initials: FF
authors.lastname: Huang
authors.forename: Hui-Xuan
authors.initials: HX
authors.lastname: Liao
authors.forename: Shao-Lin
authors.initials: SL
authors.lastname: Peng
mesh_terms: D000220:Adaptation, Biological / Q000502:physiology*; D000704:Analysis of Variance; D018533:Biomass; D002681:China; D003710:Demography; D060434:Herbivory; D058865:Introduced Species / Q000706:statistics & numerical data*; D027741:Ipomoea / Q000254:growth & development*; D018515:Plant Leaves / Q000737:chemistry; D054712:Salinity; D013045:Species Specificity; D018709:Statistics, Nonparametric; D013312:Stress, Physiological / Q000502:physiology*; D013634:Tannins / Q000032:analysis; D053833:Wetlands
chemical_list: D013634:Tannins