Laws Of Vegegation Community Succession And Strategies Of Restoration In Inner-River Wetland In Zhenjiang

Wetland is called "the cradle of mankind", "a gene pool of living things" and "thekidney of nature" because of huge productiveness, ecological and environmental values.Wetland, forest and ocean are the three most important ecosystems on earth. With theviolent increase of world population and rapid development of economy, wetland degradesfor the changes of ecological character in wetlands ecosystem including decrease inwetland area, water pollution, biodiversity reduction and weakened function of wetland formankind disturbing since 20th century. Some effective measures are adopted to prevent thedegradation of wetland in many countries around world and the study on restoration andrebuild of degraded wetland ecosystem has been a focus in the past 20 years. Many workshave been done in studying wetland ecosystem in plain and northern peat land, but little isreported on the same work at Zhenjiang Inner-river wetland, which is a micro-wetlandnearby the city.The Inner-river wetland lied to the north of zhenjiang city, and formed from thesediments of nudes and sands which taken by Yangtse Rive. There were vegetables inabundance on this wetland, but in recent years, the plant communities of wetland weredestroyed and ecology functions were impaired resulted form contamination discharge andfishing action by mowing. In this paper, by studying the law of community succession,probe into the measures degraded Vegetation restoration. The results as follow:The vegetation succession of Inner-river in Zhenjiang belongs to primary nakedsuccession, Phalaris arundunacea acetd as because of its high stress resistance, and thencommunity succession began. It begins from naked land, and then go along Phalarisarundunacea community, Phalaris arundunacea-Phragmites communis community, andreach climax community—Phragmites communis community in the end.By using the space series to replace time courses, we chosen four typical samplingstanding for above four different successive stages in Inner-river wetland, and investigatedthe laws of community of vegetation community, e.g., species composition, speciesdiversity and life-form, and then discovery restoration approaches of degraded community. The results showed that the species diversity, species composition andlife-form along different successive stages were different significantly. In general, therewere an increasing trend in species richness and species diversity along different successivestages, but the maximum is in the mid-last successive stages. The evenness index increasedcontinuously, while ecological dominance declined progressively along with succession.For life-form composition, along with succession processes, the importance value ofperennial herbaceous plants declined firstly and then increased, while the species number ofperennial herbaceous plants increased gradually and became relativelysteady in latersuccessive stages. As to annual-biennial herbaceous plants, the importance value andspecies number increased firstly, and then declined. However, perennial herbaceous plantswere dominant in all successive stage. For the total number of family and genera, itincreased gradually as succession proceeded, and Gramineae were dominance species at alltime.In whole succession series, the niche breadths of Phalaris arundunacea andPhragmites communis populations are higher. It accounts for they take up more wide lifespaces and make full use of resources and then become dominant species of community.When Phragmites communis come into being, its niche breadths increase rapidly, but theniche breadth of Phalaris arundunacea decrease. At last, the niche breadth of Phragmitescommunis become the most, it acts as monodominant species of community accordingly. Assuccession process, the niche breadths of some hydrophytes and phreatophytes go down,while that of xerophils goes up. It illuminates the community succession is becoming moresuit for xerophils.At the beginning, species in the wetland is few, while resources are available inabundance; the coefficient of niche overlaps of population is small. Along with successionadvance, species increase, and the coefficient of niche overlaps of population ascendsimultaneity. The mean coefficient of niche overlaps goes up also. When succession goesinto mid-last stages, the coefficient of niche overlap reaches tiptop. Subsequently, the nicheseparates, the community tends to stabilization, and all those show the climax community isgoing to come.In order to find out the diurnal dynamics of microclimate within different successivestages of vegetation communities in inner-river wetland, and probe into the interactionbetween vegetation and environment Three typical communities were chosen and stand fordifferent successive stages of vegetation succession respectively, and then measured the light intensity, air and soil temperature, air relative humidity. The results showed that alongwith communities advanced which was naked land→Phalaris arundinacea→Phragmitescommunis, light intensity, air and soil temperatures decreased while relative humidityincreased significantly, and the daily variations decreased. While air relative humidityincreased, mean diurnal variation decline. Habitats were open at early-succession stage andmore closed at late-succession stage, and microclimate conditions developed towardsenvironments with much more cloudy, cold and moist properties, and fluctuation of themicroclimate was decreasing, stability of the microclimate was increasing. There was somecertain correlativity among light intensity, air temperature, air relative humidity and soiltemperature in the vegetation communities, but relational coefficients between factors ofmicroclimate were discrepancy in different successive stages.With succession going along, the general nutrient status of soil gets better. Soil organicmatter, total nitrogen and available phosphorus all ascend, only available Potassiumdescends in Phragmites communis community, which because lots of Phragmites communiswere mowed and then taken out of wetland ecosystem. The vertical distributions of allnutrient ingredients are different because of the differences in the distribution roots andamount of deadwood.By analyzing seasonal growing dynamics of growing indices of Phalarisarundinacea, Phragmites communis with logistic model, results showed the logistic fittingcurves are good. In addition, the innate rate of increase r and the environmental capacity Kof every growing index of Phragmites communis are higher than that of Phalarisarundinacea. To a certain degree, it manifests Phragmites communis has more productive.The differences of photosynthetic characteristics between Phragmite communis andPhalaris arundinacea were studied by using portable LI-6400 photosynthesis instrument(Licor. USA) to measure the diurnal changes of net photosynthetic rate and its majoraffecting factors, including photosynthetically active radiation (Par), stomatal conductance(Cond), intercellar CO₂ concentration (Ci), leaves temperature (T1), air temperature (Ta),transpiration rate (Tr). The results showed that the diurnal process of photosynthetic rate oftwo exhibited a double peak curve. This may reflected an obvious phenomena of middaydepression of photosynthesis, but the reasons resulted in midday depression are different inboth plants. The midday depression of Phragmite communis caused by stomatal limition,that of Phalaris arundinacea by Non stomatal limition. The light saturation points of bothplants are so high that natural light intensity couldn't reach, from which it could be concluded that both Phalaris arundinacea and Phragmite communis are a kind plant withhigh light use efficiency. As for net photosynthetic rate, apparent quantum yield,carboxylation rate, Phragmite communis surpasses Phalaris arundinacea, therefore, lightuse efficiency of Phragmite communis is higher than that of Phalaris arundinacea.However, the light compensation point ofPhalaris arundinacea is rather low, which makesit can grow well and slows the course that Phragmite communis replace Phalarisarundinacea, and makes the succession is a long-termed process.By modifying replacement series experiment properly on the basis of hypothesis, thecompetitive characteristics of dominant species Phalaris arundinac and Phragmitecommunis in plant community succession process in inner-fiver wetland in Zhenjiang werestudied. The results showed that both Phalaris arundinac and Phragmite communisexploited different resources in different density mixture conditions, and presentedsymbiosis to some degree, but at same time obvious competitive was put up. Phragmitecommunis was superior to Phalaris arundinac in the competitive ratio. As far as themorphology and Physiology, the competitive made inferior position species Phalarisarundinac the number of ramification decrease, the plant height reduce, the values of SPADand net photosynthetic rate lessen. So in the community succession process, Phragmitecommunis population will replace Phalaris arundinac population certainly, and become thedominant population at next succession stage.Taking a piece of wetland link to sewage outfall of the Dadonggou as example, bycomparing vegetation community with other piece of wetland which is same in successionstages, and then analyze effects of human disturbances on vegetation and communitysuccession. Results showed, vegetation community in Inner-river is in moderated-degradedstation caused by contamination discharge and fishing action by enclosing some areas withnets. In restoration, according to Secondary succession theory and Self-design theory, adoptengineering techniques to control contamination discharge, and then restore to primaryconditions, and take technology of cultivation to accelerate vegetation restoration.