| Due to the continuous development of the global economy and trade, frequency of human activities and the intercourse have been accelerated, and biological invasion has globally spreaded up. Besides, plant invasions plays an important role in biological invasion, which have become a serious environmental and socioeconomic problem and a hot topic of ecological research worldwide. Invasive Asteraceae species are also important components of invasive plants, however, the photosynthesis of green plants is a mechanism of their survival, in order to study the mechanism invasion behind invasive plants, we take Asteraceae invasive plants including Mikania micrantha, Ageratina adenophora, Chromolaena odorata and Bidens pilosa, Parthenium hysterophorus, Flaveria bidentis, Ambrosia artemisiifolia, Ambrosia trifida as the objects of the study, and their co-occuring native Asteraceae plants as the control, studying the difference between invasive plants and their co-occuring natives in gas exchange characteristics. Ecophysiological traits including net photosynthetic rate (Pn), water use efficiency (WUE), photosynthetic nitrogen use efficiency (PNUE), photosynthetic energy use efficiency (PEUE), specific leaf area (SLA), leaf P content per unit mass (Pmass), leaf N content per unit mass (Nmass), chlorophyll content, and mass-based and area-based leaf construction cost (CCmass and CCarea) were measured. The main results are presented as follows:The difference in gas exchange characteristics between Asteraceae invasive plants which include Mikania micrantha, Ageratina adenophora, Chromolaena odorata and Bidens pilosa, and their co-occuring Asteraceae plants Ageratum houstonianum in Yunnan have been analysed. The results showed that:the maximum net photosynthetic rate (Pnmax) of M. micrantha, A. adenophora, C. odorata and B. pilosa were 15.921,18.688,17.151 and 22.775 μmolm-2·s-1 respectively, significantly higher than that of A. houstonianum by 21.63,42.77, 31.02,73.99 percent, respectively. Light saturation point (LSP) and light compensation point(LCP) of four invasive plants were also significantly higher than that of A. houstonianum, but significantly lower than that of latter in apparent quantum yield(AQY). PEUE and PNUE of the four invaders were also significantly higher than native plants with exception of C. odorata. Correlation analysis indicated that Nmass was positively correlated with leaf SLA, CCmass, Pnmax,Pmass and PEUE, while Pnmaxwas positively correlated with leaf SLA, PNUE and PEUE.The difference in gas exchange characteristics between Asteraceae invasive plants Parthenium hysterophorus and Bidens pilosa, and their co-occuring native Asteraceae plants Cirsium setosum have been analysed. The results show that the Pn, chlorophyll content, leaf SLA, leaf Pmass, PEUE, and PNUE of P. hysterophorus and B. pilosa were significantly higher than those of C. setosum. Stomatal conductance (Gs), transpiration rate (Tr), leaf Nmass, and leaf CCmass of P. hysterophorus were significantly higher than those of C. setosum, only. Correlation analysis demonstrated that leaf WUE, Pmass and SLA were significantly positively correlated with Pn. Leaf CCmass did not increase significantly with increasing Pn. Leaf SLA, CCmass, and chlorophyll content were significantly positively correlated with Nmass-Compared with native plants, higher gas exchange characteristics and leaf biochemical indicators may contribute to the successful invasion of P. hysterophorus and B, pilosa.Analysis of the differences in gas exchange characteristics between Asteraceae invasive plants Flaveria bidentis and its co-occuring native Asteraceae plants Xanthium sibiricum in three different areas in Hebei.The results showed that:the LSP of the two species from three regions are all higher than 1200 μmol·m-2·s-1, and the LSP of F. bidentis was significantly higher than that of native species in Handan and Hengshui; but F. bidentis collected from the three areas were significantly lower than X. sibiricumin LCP. Except for Hengshui area, F. bidentis of the other two regions were also significantly lower than that of native species in AQY; the Pnmax of F. bidentis in three areas was significantly higher than that of X. sibiricum by 42.77,221.80,122.88 percent, respectively; the difference of invasive plants in three regions in chlorophyll content was not significant campared with their natives.In addition to Handan, the SLA, PNUE of F. bidentis in the other two areas were significantly higher than X. sibiricum, and the Nmass, Pmass, PEUE of F. bidentis were significantly higher than that of native species. Correlation analysis has indicated that the plants Pnmax was positively correlated with CCmass, Nmass, Pmass, PEUE and PNUE; Nmass was positively correlated with SLA, CCmass,Pmass, leaf SLA was positively correlated with PEUE and PNUE.The difference in gas exchange characteristics between Asteraceae invasive plants Ambrosia artemisiifolia, Ambrosia trifida and their co-occuring native Asteraceae plants Aster tataricus were analyzed. The results showed that the Pn curve of the three plant species are significant correlated with photosynthetically active radiation(PAR). The LSP of A. artemisiifolia, A. trifida were were significantly higher than the native species A. tataricus. The order of Pnmax was that A. artemisiifolia>A. trifida>A. tataricus, and the invisive species were significantly higher than that of A. tataricus by 151.28,82.80 percent respectively. The SLA, Nmass,Pmass, PEUE, PNUE of invasive plants were significantly higher than the natives, but the difference of CCmass between the three plant species was not significant. Correlation analysis results showed that Pnmax was significant positively correlated with Nmass, SLA, PNUE and PEUE; Nmass was significant positively correlated with leaf SLA, CCmass, Pmass, PEUE was significant positively correlated with leaf SLA and PNUE, there was also a significant positive correlation between PNUE and SLA.Comprehensive analysis showed that the major domestic Asteraceae invasive plants has higher gas exchange characteristics and leaf traits compared with non-invasive plant species, what’s more, the photosynthetic characteristics and leaf characteristics of all plants are closely linked. The main Asteraceae invasive plants have higher photosynthetic characteristics and energy use indicators, like Pnmax, PNUE, PEUE, WUE and other indicators, leading to more effectively capturing and using the environmental resources, which may be one of the reasons to successful invasion of the main Asteraceae invasive plants. |
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