Response Of Native And Invasive Triadica Sebifera To Major Global Change Factors

Plant invasions have already been recognized as an important component of global change. Plant invasions and other global change factors are closely related and they will interact with each other. In the era of global change, we should pay more attention to effects of other global change factors on invasive plants so that we have a better understanding the dynamic of invasive plants. Elevated carbon dioxide ?CO₂? and surface ozone ?O₃?concentration, enhanced ultraviolet -B ?UV-B? radiation and nitrogen deposition are all very important issues of global change. The change of those environmental factors will definitely influence the growth and reproduction of plants, alter the structure of community and even impact the direction of ecosystem succession. Furthermore, abiotic factors will also interact with each other so that their combined effects on plants will be non-additive.So far, the interactive effects among those environmental change factors on plant's performance are unknown, especially their interactive effects on the performance of invasive plants. Why can invasive plants successfully invade a new area? One reason is that invasive plants themselves have strong invasiveness ?intrinsic properties? and the other reason is the low community invasibility ?extrinsic pressures?. The abiotic and biotic factors in the area both determine the invisibility. The changes of environmental factors might affect the invasiveness for the invasive plants and the competition between invasive plants and native biota ?e.g. native species?. In addition, when the invasive species invaded the new area, their inherent traits or genetic characters might be changed in order to adapt to the new environment. Hence, the responses of invasive and native ecotypes to abiotic changes might differ. In this paper, we focused on the elevated surface O₃ interacting with other global change factors, selected Triadica sebifera as the focused model plant, and conducted two controlled-environmental-chamber experiments and two open-top- chamber experiments which were: ?1? response of the performance for invasive T. sebifera and three native species to elevated surface O₃ and CO₂ concentration; ?2? response of the performance for invasive and native populations of T. sebifera to elevated O₃ and CO₂ concentration; ?3? effects of elevated O₃ concentration and UV-B radiation on the growth of invasive and native populations of T. sebifera; ?4? effects of elevated O₃ concentration and nitrogen deposition on the growth of invasive and native populations of T. sebifera.The important findings are presented as follows:1. Compared with 3 co-occurring native species, invasive T. sebifera was more vigorous and had lower condensed tannin content. When performances of native and invasive populations of T. sebifera were compared with or without competition, we found that biomass, plant height and other growth traits were greater for the seedlings from invasive populations relative to that from native populations. Especially, those difference of traits were more evident in the experiment with intraspecific competition. The results showed that invasive population of T. sebifera evolved allocation away from costly secondary metabolites towards growth after they were introduced, so that invasive populations of T. sebifera outperformed the native populations of T. sebifera or native species in the invasive range. The result was consistent with evolution of increased competitive ability hypothesis ?EICA?.2. Invasive populations of T. sebifera were more sensitive to elevated UV-B than native populations. Furthermore, litter mass of invasive and native populations showed opposite responses to elevated UV-B. UV-B increased litter mass of native populations but decreased litter mass of invasive populations. The outcome might change the process of nutritious cycling in soil leading to influence invasion success. These results revealed that changes in traits allowed invasive population of T. sebifera to become a successful invader,but those changes also make them especially sensitive to elevated UV-B which obeyed a"master of some" scenario of plasticity. "Master of some" pattern means an invader can be better able to increase fitness in mild environment but not suitable to success in stressful environment, such as elevated UV-B radiation. In addition, total biomass was higher for invasive populations of T. sebifera relative to native in combined elevated O₃ and CO₂ concentration, and the difference is significant higher than that in ambient condition.However, there was no detectable difference in total biomass between invasive and native populations under elevated O₃ alone. Meanwhile, the leaf number of invasive populations was lower than native population under O₃ alone. In our study, combined elevated O₃ and CO₂ concentration was a mild environment which was suitable for plant growth. Hence, it also showed the evidence that invasive T. sebifera corresponded to a "master of some"pattern.3. Elevated O₃ concentration or UV-B radiation had negative effects on the growth of plants,and enhanced CO₂ or nitrogen deposition would improve the seedlings' performance.O₃ and CO₂ had interactive effects on plants during the early growth stage in ways that the seedlings grew better under the condition of combined elevated O₃ and CO₂ than at elevated CO₂ levels. O₃ also interacted with UV-B. Elevated UV-B could ameliorate the detrimental effects of O₃ or increase the plant tolerance in response to O₃. There were no significant interactions on plant growth between O₃ and nitrogen deposition so that their combined impacts were addictive.4. In the controlled environmental experiment, elevated O₃ markedly reduced the root to shoot ratio for invasive populations of T. sebifera, but had no effects for native populations of T. sebifera. In the open top chamber experiment, elevated O₃ had no effects on root to shoot ratio for both seedlings from invasive and native range when they were planted individually. However, when native and invasive populations of T, sebifera were grown in pairwise combinations, elevated O₃ decreased the root to shoot ratio for both ecotypes.5. Elevated CO₂ significantly increased the total mass, leaf mass and leaf number for invasive T. sebifera, but there were no detectable impacts on native co-occurring plant species in elevated CO₂. Results suggested that elevated CO₂ would increase the competitive ability for invasive species which is in line with the theory of fluctuating resources: fluctuation in resource availability would promote the plant invasion.6. Nitrogen deposition significantly reduced the difference in leaf or root mass between invasive and native populations of T. sebifera, but this outcome did not change the tendency of competition. Invasive populations of T. sebifera outperformed native populations either under control or nitrogen addition treatment. In addition, nitrogen deposition also decreased the root to shoot ratio for invasive and native T. sebifera,7. There was a significant interaction of O₃ and different scenarios of nitrogen supply for difference of growth between invasive and native populations of T. sebifera. Elevated O₃ would increase the competition between invasive and native populations of T. sebifera for resources in soils. Compared with nitrogen supply in uniform scenario ?Uniform?,nitrogen supply in the middle of experiment ?Middle? or in random scenario ?Random?would foster plant invasion. The result suggested that changes in resources availability fluctuated more frequently during a short period, it would be good for invasive plants to exploit and capitalize the available resources more efficiently.First, in conclusion, there were two reasons for invasive species of T. sebifera succeeded in invading a new habitat: it was innately better competitors before invasion,meanwhile it was evolved after introduction leading to increase its competitive ability.Second, a suitable environment would promote the invasion for invasive T. sebifera, but a stressful environment would inhibit its success of invasion. In addition, stressors would enhance the intraspecific or interspecific competition for resources. Thirdly, increase in resources would promote plant invasion, and resource fluctuation would favor invasive plants utiling resources more efficiently. Finally, decrease in root to shoot ratio might be a strategy in response to environmental changes as results to increase the aboveground C allocation.