The Impact Of Climate Change On The Physiological And Ecological Characteristics Of Dominant Plants In Plateau Wetlands

Global warming has turned to be an irrefutable fact.IPCC Fifth Assessment Report has indicated that the global average surface temperature will rise by 0.3-4.8?on the basis of 1986-2005,and climate change will very likely cause longer and more frequent heat waves by the end of this century.Yunnan plateau wetland is an important ecological barrier of our country,and the wetland ecosystem is extremely fragile.Due to the high altitude,sensitive to climate change,it is more vulnerable to the impact of global warming.As the producer,the plant in plateau wetland is the core and foundation of the whole wetland ecosystem,the important indicator of the quality of wetland environment,and the most intensive part of the response to climate change.Based on the three dimensional terrain and climate,with the method of ex-situ,the dominant emergent plants in the Napahai wetland?3260m asl?,Scirpus tabernaemontani and Zizania caduciflora,together with sediment from that site were transplanted to Lashihai wetland?2437m asl?and Dianchi watershed in Kunming?1891m asl?to study the impact of climate change on the plants in plateau wetlands.The main contents and research results are summarized as follows:?1?Along with the change of climatic conditions caused by the decline of altitude gradient,air temperature and water temperature increased significantly,light intensity decreased significantly,rainfall changed significantly,while CO₂ concentration and relative humidity changed slightly.In the study of the impact of climate change on the aquatic plants in plateau wetlands,air temperature,water temperature and light intensity are the environmental factors that should be considered.CO₂ is one of the necessary materials for photosynthesis of plants,and is also a kind of environmental factors that constitute the living environment of plants,therefore,CO₂ concentration is also the environmental factor that should be considered.?2?Along with the change of climatic conditions,net photosythesis rate?Pn?of Scirpus tabernaemontani and Zizania caduciflora increased significantly.After transplantation from Napahai wetland to Lashihai wetland and Dianchi watershed in Kunming,the average net photosynthetic rate?Pn?of Scirpus tabernaemontani in growing stage increased by 19.1% and 18.4%,and that of Zizania caduciflora increased by 43.5% and 44.2%.Meanwhile,stomatal conductance?Gs?,intercellular CO₂ concentration?Ci?and transpiration rate?Tr?increased significantly.Maximum net photosynthetic rate?Pmax?,light compensation point?LCP?and apparent quantum yield?AQY?increased significantly,while light saturation point?LSP?decreased significantly.CO₂ compensation point?CCP?decreased significantly,while CO₂ saturation point?CCP?and carboxylation efficiency?CE?increased significantly.Research showed that Pn of the two species of plants in different climatic conditions was significantly or extremely positively correlated with the physiological factors of Gs,Ci and Tr,while air temperature in different climatic conditions was the most important environmental factor affecting the photosynthesis of the two species of wetland plants.Although the two species of tested plants were widespread species,the regulation mechanism in stomatal conductance of Zizania caduciflora was better than Scirpus tabernaemontani.Therefore,the correlation between Pn and air temperature was higher than that of Scirpus tabernaemontani,and Zizania caduciflora reflected the high adaptability to air temperature rise.Temperature rise caused by climate change greatly promoted the light energy use efficiency of the two species of plants,and the photosynthetic carbon sequestration capacity has been greatly improved.?3?Along with the change of climatic conditions,plant heights and biomass of Scirpus tabernaemontani and Zizania caduciflora increased significantly.After transplantation from Napahai wetland to Lashihai wetland and Dianchi watershed in Kunming,the biomass of Scirpus tabernaemontani in late stage increased by 20.3% and 22.5%,and that of Zizania caduciflora increased by 42.2% and 45.3%.However,the variation of stem diameters was not significant.Therefore,the stems of these two species were not robust,easy to lodging,and it was not conducive for the plant to resist the external environment.In addition,the adaptability of plant heights and biomass of Zizania caduciflora to air temperature rise was higher than Scirpus tabernaemontani.Research showed that air temperature in different climatic conditions was the most important environmental factor affecting plant heights and biomass of the two species of wetland plants.The species of plants,which were widely adaptable and tolerant to temperatures,could actively respond to climate warming.The photosynthetic carbon sequestration capacity and bilmass of these plants could also be increased significantly,resulting in a positive impact on the carbon input of ecosystem.?4?Along with the change of climatic conditions,chlorophyll content of Scirpus tabernaemontani and Zizania caduciflora increased significantly,while the contents of malondialdehyde,peroxidase,free proline and soluble sugar decreased in different degrees.Along with the change of climatic conditions,the change of free proline content of Scirpus tabernaemontani was gradually smaller in seasonal dynamic,while that of Zizania caduciflora was still great.Except free proline,the other physiological and biochemical characteristics of Zizania caduciflora increased or decreased greatly than Scirpus tabernaemontani.Research showed that air temperature in different climatic conditions was the most important environmental factor affecting physiological and biochemical characteristics of the two species of wetland plants,except for Peroxidase.Overall,the two species of wetland plants both reflected the adaptability of widespread species to climate warming,however,the adaptability of Zizania caduciflora to environmental stress was stronger,and this was conducive to the further growth and expansion,then to maintain the dominant position in the wetland ecosystem.?5?Along with the change of climatic conditions,the decomposition rate of litter of Scirpus tabernaemontani and Zizania caduciflora increased significantly.After transplantation from Napahai wetland to Lashihai wetland and Dianchi watershed in Kunming,the decomposition rate of Scirpus tabernaemontani increased by 31.9% and 28.9%,and that of Zizania caduciflora increased by 44.7% and 43.6%.The order of temperature sensitivity of litter decomposition(Q₁₀)was mixed litter?3.48?>Zizania caduciflora?3.06?>Scirpus tabernaemontani?2.52?,therefore,the impact of water temperature on the litter decomposition of Zizania caduciflora was higher than Scirpus tabernaemontani.The decomposition rate was significantly correlated with water temperature during the plant growing seasons and with litter quality during the winters.In our study,concentrations of C,N,lignin,and the ratios of C:N,and lignin:N in litter were the most important predictors of decomposition rate,but the relationships between decomposition rate and litter nutrient concentrations or their ratios varied over the different decomposition periods.In particular,N concentration and the ratio of C:N were the most significant factors influencing the decomposition rate during the first winter,while the ratio of lignin:N was the most significant factor during the second winter.Research showed that water temperature in different climatic conditions was the most important environmental factor affecting litter decomposition of the two species of wetland plants,then was the litter quality.Climate warming could accelerate the litter decomposition of widespread species of wetland aquatic plants,especially the decomposition of mixed litter,then increase the carbon output from the plateau wetland ecosystem.?6?The impact of climate warming on the carbon pool of the plateau wetland ecosystem is not unilateral,which affect the balance of soil carbon pool in the wetland by carbon input and output.Climatic factors determine the distribution of vegetation species,the production of photosynthetic products and the decomposition rate of litter,therefore,they have great influences on the soil organic carbon sequestration and mineralization decomposition process.Overall,the promotion of climate change to the litter decomposition of Scirpus tabernaemontani was greater than to the photosynthetic carbon sequestration ability,while it was basically equal to that of Zizania caduciflora.Under the background of global warming,Scirpus tabernaemontani may weaken the carbon sink function of the plateau wetland ecosystem,while Zizania caduciflora may has little effect on the carbon sink function of this ecosystem.The impact of climate warming on the carbon balance of the plateau wetland ecosystem is a complex and comprehensive process,which needs further research.