PS 16-154
Nutrient addition amplifies salinity-dependent differences in competitive ability of invasive and native vines

Monday, August 5, 2013
Exhibit Hall B, Minneapolis Convention Center
Gang Liu, School of Life Science, Sun Yat-sen University, Guangzhou, China
Evan Siemann, Department of Ecology and Evolutionary Biology, Rice University, Houston
Shaolin Peng, School of life science, Sun Yat-sen University, Guangzhou
Invasive plants are usually thought to have lower competitive ability than native species in habitats with limited resources. Resource enrichment caused by anthropogenic activities is thought to facilitate invasions by creating conditions in which the competitive ability of invasive plants is greater than that of native species. However, it is not clear whether such increased resource availability will increase invasion success in stressful habitats such as coastal areas with high soil salinity. We hypothesized that the competitive dynamic between invasive and native plants in stressful habitats would not be as sensitive to resource enrichment as in benign conditions and so would reflect interactions of these environmental factors (soil salinity and soil nutrients).
We conducted a greenhouse experiment in China using the invasive vine Ipomoea cairica, which is expanding into saline coastal areas from non-saline habitats, and the widespread native vine Merremia hederacea, which is also expanding its range. Pots received two plants (pair of invasive vines, pair of native vines, or one of each vine species) and were assigned nutrient (control vs. Hoagland’s solution) and salinity stress (control vs. 4g L-1NaCl solution) treatments in a factorial design.
Overall, masses of invasive and native vines did not differ. Salinity decreased plant mass and nutrients increased plant mass, especially without salinity stress. In every combination of treatments, invasive vines were larger than native vines in single species pots. However, without salinity (low stress), native vines were significantly larger than invasive vines when they were competing in the same pot. Nutrient addition increased the competitive advantage of native vines in low stress conditions. In saline conditions, the opposite pattern was found. Mainly, invasive vines had greater competitive ability which was increased by nutrient addition.
Our results indicated competitive ability of the two species depended on salinity and that nutrient addition only magnified the differences between these two species. This suggests that nutrient addition may increase invasion success but only in habitats where conditions were already suitable for invasion. The mismatch between the results for growth in monoculture pots versus competition pots suggests caution in inferring the effects of environmental factors on competition based on measures of individual performance. The strong positive effects of salinity and nutrient addition on the relative competitive ability of I. cairica suggest that anthropogenic nutrient addition will facilitate its secondary invasion in coastal areas in China.