Coastal Wetland Plant Functional Traits And Its Ecological Environment Adaptation Strategy Research

Under the background of global changes, the growing habitats of plants often experience the changes from safety, warm, wet to high temperature(low temperature), barren, drought, and even pollution. Plants can acquire the ability of resisting the special external environment through the changes of structure and function, namely the evolutionary adaptation mechanism. The coastal wetland lies between terrestrial and marine ecosystems, the coupling of waterlogging and salinity is obvious. In addition, the coastal areas are easily disturbed by human activities, which create the unique biogeochemical cycles and environments in there. This thesis chooses the typical plant communities(Suaeda salsa, Phragmites australis and Tamarix chinensis) of coastal wetlands in Dongying and Tianjin as the research objectives. The important functional traits, including photosynthetic traits, stoichiometric traits and heavy metals enrichmental properties were performed to explore the adaptive strategies of wetland plants in the severe habitats(high salt, flooding and heavy metal pollution) of coastal wetlands. Those explorations in functional traits and adaptive strategies of coastal plants can provide theoretical and technical support for coastal wetland restoration. The results showed as follows:1. Comparing with the different communities, the above-ground N and the under-ground N and P of S. salsa were lower than that of P. australis and T. chinensis, while the above-ground P and N/P ratio of T. chinensis were higher than that of P. australis and S. salsa. For the three typical wetland communities, the N content of the above-ground biomass were higher than that of the under-ground biomass indicating that nutrition N tended to be allocated to the above-ground photosynthetic apparatus in the N-limited habitat. However, the opposite trend existed between the P content variations of above and under-ground biomass of T. chinensis and S. salsa, which revealed that species in different successional status would adopt different strategies to adapt to various environments. Unlike the woody species of T. chinensis, the above-ground biomass of P. australis and S. salsa had higher N/P ratios than the under-ground biomass, and this was possibly relate to the high relative growth rate of the above-ground organs of herbaceous species.2. The soil N content and N/P ratio decreased with the soil depth increasing in the coastal wetland of Dongying, while no obvious changes of soil P were found along the vertical soil profile. The weak correlations between the top soil(source) and the plant organs(pool) suggested that, physiological accommodation of coastal wetland plants played some roles in N / P stoichiometric regulation besides soil conditions.3. The salinity of Tianjin coastal wetland was significantly higher than that of Dongying, and the net photosynthetic rate(Pn) of Suaeda salsa and Phragmites australis in Tianjin were also higher than those of Dongying, which meant that the plants can accumulate more carbon assimilation though raise the photosynthetic rate to resist high salt stress habitat. While the low transpiration rate(E) and the vapour pressure deficit(VPD) may be a compensation mechanism to the water defict in high salinity stress. Compared with the different plants in one site, Pn, E and Gs of Phragmites australis were higher than Suaeda salsa, which is probably dominated by the different leaves constructions of the two plants. At the species scale, the significant linear relationships between photosynthesis and N/P ratios also suggested that the regulation of plant photosynthesis on N/P stoichiometry.4. The mean value of N/P in Dongying coastal wetland of Suaeda salsa was 13.76, and the mean value of N/P of Phragmites australis was 23.47. However, the mean value of N/P in Tianjin coastal wetland of Suaeda salsa was 8.23, and the Phragmites australis of N/P was 8.19. N/P ratios of the two species in Dongying coastal wetland were significantly higher than those in Tianjin, which suggest that Tianjin coastal wetland plants are mainly affected by N limitation. While the coastal wetland plants of Dongying are mainly affected by N and P common limitation. The photosynthetic nitrogen use efficiency(PNUE) of Suaeda salsa and Phragmites australis in Tianjin were significantly higher than those of Dongying. On the other hand, the photosynthetic phosphorus use efficiency(PPUE) of Phragmites australis in Dongying was significantly higher than that in Tianjin. The results imply that coastal plants tend to increase their PNUE and PPUE to compensate nutrient deficiency.5. The enrichment coefficients of As, Cu, Ni, Sr and Zn for Suaeda salsa under the condition of sandy and non-waterlogging were higher than in clay and waterlogging, clay and non-waterlogging habitats, however, the transfer coefficients of these heavy metals were not follow as above. In addition, no significant differences were found between latter two habitats, which indicated that flooding did not alter the heavy metal enrichment characteristics of Suaeda salsa. However, these functional traits strongly correlated to soil types, for example, the low soil organic matter and salinity, the large p H can stimulate plants increasing their enrichment coefficient, but the translative ability of heavy metals in plants does not increase.6. The enrichment capacity of coastal wetland plants are proved to be correlated with the types of heavy metals. Suaeda salsa of Tianjin coastal wetland has high transfer ability for Cr and Pb in sandy and non-waterlogging habitat, and low transfer ability to Mn, Sr and Zn. These results indicated that the transfers of plants to heavy metals are selective. Use a multivariate analysis, we found that the heavy metals of Zn and Cr in Tianjin coastal wetland may come from the external input, however, the heavy metals of Ni, Cu, Pb, Sr and Mn probably originate from natural factors. Further more, the heavy metal of As in Tianjin coastal wetland is likely to be affected by the two factors.