| According to scientific investigation,among all developments and construction activities,famrming and forest exploitation,road construction,town construction,coal mining,irrigation works and power generation cause the most serious soil erosion.The construction of roads,railways and irrigation works,which are not only large on scale and rich in number,but also widely involved and closely related to natural environment.The large amount of bare slopes resulted from soil and stone excavation and stuffing destroy original vegetation,and these all have negative effect on local entironment.Therefore,the combination of project development and environment protection has become an important task for sustainable economic development.In the past,simple protection techniques such as wet or dry brick-laying and spraying protection techniques were used,which caused destroyed vegetation,poor ecological scenery and other ecological problems.At the same time,the problems of high cost for project construction,latter vegetation of slope deterioration and high conservation cost are outstanding.At present,slope treatment has developed to the stage of slope protection and ecological restoration,but ecological restoration needs a relatively long time and in our country the theory of restoration ecology has just been introduced in slope restoration recently,so there are few papers in this respect,and they are only notional introduction,few study results have been known.Therefore,further exploration into substance and energy recycle,restoration process,etc in slope protection and virescence are needed to learn the functions of vegetation in slope stabilizing on the level of ecosystem and consider economic problems in slope protection and ecology restoration with ecology-economic theory.In recent years,the study on and the application of Vetiveria zizanioides are carded out very widely both domestic and abroad.But they emphasized on applied study,lacking systemic,deep study and summary.As a pioneer introduced species,it is difficult to tell and determine Vetiveria zizanioides succession role in restoration.At present,its function and role in community succession and the mechanics of its effect on succession orientation and process are still unknown.Most engineering slopes are highly steep,dry in autumn and in winter and hot in summer,and nutrients in the soil gradually leak,causing low soil fertility,thus,how to solve the problems of no soil,shortness of water and fertility and the threat of dryness and hotness that the slope vegetation is faced with will directly effect the final virescence results and the function of ecology effectiveness.Therefore,to learn the natural environment information on the slope and the physiological and ecological characters is the key to the success of plant slope protection.This study was designed to address a physiological and ecological exploration based on the effects of main limiting factors in vegetation slope protection such natural factors as temperature,moisture,light,etc.and such artificial measure as cutting on virescence growth,which the tolerance thresholds of these factors were determined by and used as the theory gist of community succession characters.The study results showed that under the hot and wet conditions in summer, vetiver tolerated 55℃,and water stress time may last 24 to 42 days.The exterior configuration changes and interior physiological and ecological changes in the aboveground parts and the underground root system resulted from high temperature and dryness not only suppressed the growth of aboveground parts,but also caused relative changes in leaf shape.In addition,it affected the normal physiological functions of the leaves,resulting in decrease in the value of SPAD and increase in leaf injure rate.Despite initial growth improvement in root system as a result of high temperature and dryness,as the hot and dry condition continued,the root growth was obviously suppressed.In winter low temperature water-stress experiment,Vetiveria zizanioides showed fairly strong dryness tolerance,continuous dryness lasted up to 4 months.Vetiveria zizanioides also showed obvious interactive effect.Under high temperature,higher soil moisture resulted in better high temperature tolerance.Under low temperature,excessive or inadequate soil moisture limits Vetiveria zizanioides'revival in spring and its latter growth and development.In actual engineering slope protection,investigation of natural factors such as temperature of the slope site the temporal and spatial distribution regulation of slope soil moisture are needed to predict and judge whether the slope is suitable for Vetiveria zizanioides planting. Shading has different effects on different growth indexs,even the same growth character was influenced differently during various growth stages.The experiment results indicated that the recovery time is long after transplanting,with stable survival rate after 2 months. Shading affects survival rate,but not significantly.Shading in the recovery stage of 2 months after transplanting hardly affected tillers,but later,shading influences tillers very significantly.Shading hardly affects prophase height,but affects later height more strongly. Shading has a rather strong effect on root -stem ratio,which is complex.In mid-growth stage,large amounts of tillers were produced while root system developed rapidly.A proper cutting measure(Cutting one time between the middle decades of July and the middle decades of September) is beneficial to growth and development of Vetiveria zizanioides,but excessive cutting or no cutting is disadvantage to its growth.In actual slope protection practice,because of time limit,vegetation protection system will not be satisfactory after several years,although it was qualified when checked and accepted.Lacking of long- time observation and systemic study causes great difference between the situations when accepted and those years later.Only when these problems have been investigated and studied particularly,can construction be conducted properly. Otherwise,the succession of slope vegetation from enforced artificial virescence to primitive plant communities cannot be successfully realized.In this study,community character indexes of the investigated slope plant communities are observed and investigated by the same means in springs and autumns of two continuous years.Community character indices such as the species,coverage,height,density,aboveground biomass of each plant and frequency were recorded.The succession laws of all types of slope plant communities are studied through Vetiveria zizanioides population dynamic,species composition of each community and their life styles,community quality characteristics,richness index,diversity index,evenness index,ecological dominance,similarity coefficient,niche breadth and niche overlap.Slope orientation and slope location treatments are important nature factors,which influences the community features with vetiver for slope-protection.By Anlysing the investigation data of plant communities in different three type sites,the results indicates that:①Vetiveria zizanioides for slope-protection community succession is affected not only by Slope orientation(difference in light and temperature),but also by slope location(difference in soil moisture and fertility) among which light is of most importance.②Comparability coefficient between the communities at the different locations on the same slope site is greater than that between the two communities at the different slope orientation sites.③On the slope exposed to sun or slope location with preferable sun light,Vetiveria zizanioides population dominance is significant,while on the slope backed to sun or slope location with lacking sun light Vetiveria zizanioides population degrades with time,and its water and soil conservation function decreases.④Community qulity eigenvalues are closely related to the population features of vetiver,and community qulity eigenvalues are some relatively with species dominance of vetiver.When population dominance of vetiver is significant,species dominance of vetiver is negative in linearity correlation with community richness index,community diversity index,community evenness index,yet species dominance of vetiver is positive in linearity correlation with community ecological dominance index.When the population dominance of vetiver is no significant,species dominance of vetiver exists no correlation with community qulity eigenvalues.Gradient is another important nature factors,which influences the community features with vetiver for slope-protection.By Anlysing the investigation data of plant communities on different gradient slopes,the results indicates that:①They began to put up with differentiation tendency when after the two plant communities with vetiver for slope-protection on the different gradient slopes were built for two years.Less gradient slope(approximate 20°) is propitious to the development of vetiver population,at the same time it is also useful to the native plant species for settling and living.②In spring the plant community richness index of more gradient slope(approximate 30°) is greater than that of less gradient slope(approximate 20°),and community diversity index of less gradient slope (approximate 20°) is greater than that of more gradient slope(approximate 30°),but the result is reverse in autumn.In time sequence,community diversity index of less gradient slope(approximate 20°) is put up with ascend tendency;community evenness index of less gradient slope is less than that of more gradient slope;community ecological dominance index of less gradient slope is greater than that of more gradient slope,but tendency is decreased with time.③species dominance of vetiver is all negative in linearity correlation with community richness index R1,community diversity index H',community diversity index SW,community evenness index J' and community ecological dominance index C'.We found that artificial controlling direction and course of community succession, which is scientific,is feasible.So the artificial action is significative for the laws of community succession.Cutting treatment makes a great effect on developing direction and process of community succession.The result points out that①The tendency that high frequency of cutting and high richness index can be seen in the whole,but decreases the index of ecological dominance index,it is especially obvious in spring.②The treatment of cutting twice(in the fast ten days of April and June,respectively) could make a great effect on developmenting direction and process of community succession,it also could increase the number of species in community,and decrease niche overlap between Vetiveria zizanioides and other species and enhance the index of community diversity index.③Species dominance of vetiver is significant positive in linearity correlation with community richness index R1,being significant positive in linearity correlation with community richness index R2(0.01 level),being significant negative in linearity correlation with community diversity index SW,being significant begative in linearity correlation with community evenness index J',being significant positive in linearity correlation with community ecological dominance index c'.④Cutting treatment is useful to water conversation function of vegetation.The fertilizing also has a great effect on developing direction and process of community succession.The fertilizing experiment showes that:①Fertilizing could also increase the number of species in community,but it may enhance the competition effect among species.②Fertilizing also could advance the richness index of community,which is especially obvious in autumn.③Most fertilization(three times,on the earlier days in June,July and Auguest,respectively.225kg/hm~2.time) makes the community diversity index highest.More fertilization(twice times,on the earlier days in June and July, respectively.225kg/hm~2.time) is useful to increase the community ecological dominance index.④The soil moisture of fertilized community at top part of slope is higher than that at its middle part,while the unfertilized one is apt to the opposite situation.⑤The community with no fertilizing treatment is great different with that with fertilizing treatments.⑥Species dominance of vetiver is significant positive in linearity correlation with community richness index R2,being significant negative in linearity correlation with community diversity index SW,being no significant with community evenness index,yet being significant negative in linearity correlation with community ecological dominance index SN.Vetiveria zizanioides and Amorpha fruticosa Linn multiple cropping model experiment revealed that:①The population of Vetiveria zizanioides has a greater influence than that of Amorpha.fruticosa Linn.in the community.②It is harmful to Vetiveria zizanioides and helpful to Amorphafruticosa Linn.at the solar slope,while at the lunar slope we got the opposite result.③The characters of Amorpha.fruticosa Linn.were better than Vetiveria zizanioides evidently when they were intercropped at the solar slope,but the advantage was not obvious at the lunar slope.④Amorpha.fruticosa Linn.develop tall stands,thick stems with less tillers on the solar slope,on the opposite slope we got the opposite result.⑤Species dominance of vetiver is no significant in linearity correlation with community richness index,being significant negative in linearity correlation with community diversity index H'(0.01 level),being significant negative in linearity correlation with community evenness index J'(0.01 level) and community evenness index PW(0.01 level),but preferring in linearity correlation with community evenness index J'.Species dominance of vetiver is significant positive in linearity correlation with community ecological dominance index C'(0.01 level) and community ecological dominance index SN(0.01 level),but preferring in linearity correlation with community ecological dominance index C'.The results also showes that composite,gramineousness,leguminousness firstly intruded the slopes,and they all pressessed lagre proportion from 27.78%to 92.86%;There were rather great differences between community characteristics in spring and those in autumn.The community characteristics regulations in spring are complex,while the ones are comparatively obvious,so the results of investigating the plant communities is ideal when vetiver grows slowly in autumn;community characteristic values is closely related to species dominance of vetiver in the community,but different computing method of community characteristics may cause different results,so suitable assessment method is also important for community characteristics analysis and it needs further exploration.The uncertainty of eco-system restoration has already put up many levels of eco-system restoration,the ecosystem restoration requested synthetically consideration of ecology and economy and society,but it was difficult for heterogeneity of time and space. Because of the restriction of impersonality factor,the result was only on its phase.The sustaining time of ecological restoration is uncertain.It still need long-term and repeated experimentation and observation.
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