Abstract
BackgroundInvasive 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.Methodology/Principal FindingsTo 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/SignificanceThis 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.
Highlights
Biological invasions are recognized as a major driver of biodiversity decline and altered ecosystem services worldwide [1]
Our results suggest that the high tolerance of I. cairica to key stress factors contributes to its invasion into salt marshes
We addressed three main questions in this study: (1) Is the growth of the invasive species affected by simulated herbivory and salinity stress? (2) Does the invasive species have a higher tolerance to stress factors than the non-invasive species? (3) Does the invasive species exert lower resistance to herbivory than the non-invasive species, especially when herbivory pressure exists? we discuss the probability of successful invasion of salt marshes by I. cairica
Summary
Biological invasions are recognized as a major driver of biodiversity decline and altered ecosystem services worldwide [1]. Many studies have examined the relative importance of abiotic factors on the distribution of organisms in heterogeneous environments [13,14,15]. The results of these studies indicate that the boundary of a population toward the more benign end of the gradient is usually the result of competition, whereas the population boundary toward the more stressful end is mainly controlled by abiotic factors [16]. A high tolerance to stress factors may allow exotics to successfully invade stressful environments. A vigorous invader in South China, has recently been expanding into salt marshes
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