Effect Of Long-term Simulated Temperature Enhancement On The Growth And Photosynthesis Of Phragmites Australis In Tidal Wetland

Along with the rapid development of human society, the global warming which is the main feature of global change has unprecedently changed the structure and function of ecosystems since the industrial revolution. Wetlands are extremely significant in building carbon sequestration ecosystems and mitigating climate change because of their high carbon sequestration and sensibility to global change. Using the Open-top chambers (OTCs) to simulate climate warming in the future, we choose Phragmites australis in rapid growth season which are the typical vegetation of reclaimed wetland of Chongming Dongtan as research materials. The effects of long-term simulated temperature enhancement on photosynthesis, morphology and growth of P. australis were studied. At the same time, the possible mechanism of growth is discussed in terms of physiology and morphology.With research on respones of P. australis under elevated temperature, we hope to predict the adaptability of P. australis and the vegetation productivity in the region under long-term global warming.The results and conclusions are as follows:1) The effects of temperature enhancement on physiology of P. australisThe respones of the instantaneous photosynthetic process of P. australis were different between the inter-annual. After elevated temperature(ET) for one year (1aET), comparing with the control, the OTC manipulation showed positive effects.the changes of stomatal conductance(Gs) and the intercellular CO2concentration(Ci) were not significant, meanwhile, the net photosynthetic rate(Pn) and the transpiration rate(Tr) were significantly increased by26.91%,37.59%. After ET for two year (2a ET), contrary effects were exhibited. Pn and Tr were dramatically lower by11.86%,21.69%than CP. However, the temperature enhancement made the water use efficiency (WUE) aggrandized by9.81%, but the change was not remarkable. After ET for three year (3aET), there showed a negative effect between temperature enhancement and photosynthesis of P. australis. Pn,Tr and WUE were significantly reduced by19.04%,10.24%,16.94%. However, Gs and Ci hasn't show notable changes since temperature enhancement. The net photosynthetic rate-light intensity (Pn-PAR) curves showed the same trend that Pn incereased quiCPly and then hasten gentle by PAR.The curves of P.australis in OTC were up after laET and down after2aET and3aET, conparing to the CP. At the same time, after1aET, comparing with the control, the maximum net photosynthetic rate (Pmax) and the light saturation point (LSP) of P. australis in OTC were remarkably increased by11.97%,10.59%. However, Pmax was lower16.72%than CP after2aET, and the dark respiration rate (Rd) and light compensation point(LCP) were respectively decreased by19.81%,17.49%. And after3aET, situation is similar. In summary, There was a negative effect of long-term elevated temperature on P.australis.2) The effects of temperature enhancement on morphology of P. australisUnder elevated temperature, the height of P.australis showed a significant change, though the lateral growth didn't. After temperature enhancement for1a,2a and3a, the height of P.australis increased by11.5%,7.4%and1.9%, respectively. This indicated that the effects of elevated tmperature on the height of P.australis is gradually weakening. Therefore, long-term warming was not conducive to the growth of P.australis because this made it easier to lodging.Under temperature enhancement, leaf numbers and leaf area of P.australis showed significant changes. After1aET, they both increased by11.04%,10.76%. After2aET, they were higher11.67%,4.59%than CP. However, they were decreased significantly by17.39%,17.61%, respectively. The results indicated that leaf area increased or decreased with increase or decrease of the number of leaves. In addition, in the past three years of ET, the bottom leaf height of P.australis didn't show a significant change,though the leaf spacing remarkably aggrandized after laET and2aET.With increasing warming time, the gap of height of P.australis between ET and CP group continued to be narrower. The comprehensive study showed that the increase of the height was the result of increase of leaf spacing, and the effect of temperature on morphology was weakening.3) The effects of temperature enhancement on aboveground biomass of P. australisAfter1aET, the biomass of stem was increased remarkably by11.30%, but the biomass of leaf and aboveground biomass neither showed significant change. However,the biomass of leaf decreased by2.72%after2aET, at the same time, the biomass of stem and aboveground biomass were higher6.50%and3.47%than CP.After3aET, the biomass of leaf, stem and aboveground biomass respectively decreased by16.79%,5.23%and9.15%.The results indicated that short-term ET was benefit to the aboveground biomass of P.australis,but with the extension of warming time, ET was not conducive to the accumulation of aboveground biomass of P.australis.Changes in aboveground biomass of community remained consistenly with the changes in aboveground biomass of single P.australis.After1aET and2aET, the aboveground biomass of community incerased,comparing to CP. Meanwhile, there showed a more lower aboveground biomass of community after3aET. We concluded that with the extension of warming time, it would show a decreasing tendency.