Study On Dust-retention Effect And Photosynthetic Characteristics Of Urban Keynote Tree

Dust is the primary pollutant influencing the atmospheric quality of urban environment.Urban forest,as the subject of the urban ecological construction,has a great air purification effect on the dust-retention in a certain range of air,but dust pollution also have some negative effect.Keynote trees of Fuzhou(Bauhinia blakeana,Cinnamomum camphora,Ficus microcarpa,Mangifera indica)and Xiamen(Bauhinia blakeana,Winchia calophylla,Ficus altissima,Mangifera indica)were selected for the study.Analyzed dust-retention effect and photosynthetic? characteristics,and discussed photosynthetic response and resistance about the dusty leaves of different species.The results showed that:(1)Dust-retention capability has variance among different species.Dust-retention capability of keynote trees in Fuzhou as follows:Mangifera indica > Ficus microcarpa > Cinnamomum camphora > Bauhinia blakeana;the amount of plant dust-retention of keynote trees in Fuzhou as follows : Ficus microcarpa > Mangifera indica > Cinnamomum camphora > Bauhinia blakeana.Dust-retention capability of keynote trees in Xiamen as follows:Mangifera indica > Winchia calophylla > Ficus altissima > Bauhinia blakeana;the amount of plant dust-retention of keynote trees in Xiamen as follows:Mangifera indica > Ficus altissima > Winchia calophylla > Bauhinia blakeana.(2)The maximum dust-retention of keynote trees in Fuzhou and Xiamen was measured by artificial simulated dust fall.And the result was:Mangifera indica > Winchia calophylla > Ficus altissima > Ficus microcarpa > Cinnamomum camphora > Bauhinia blakeana.The results of the potential capability and trend of dust-retention of different species could be the reference to comparison of the dust-retention capability.(3)Dust-retention of species is a complex dynamic process relatively.With different seasons and cumulative time,it showed some variational regularity.Seasonal variation significantly influenced the dust-retention capability,it was bigger in spring and winter,while smaller in summer and autumn.The accumulated dust-retention of different species were increasing generally three weeks after rainning,but different species had different cumulative rate in each week.(4)The amount of dust-retention in different directions(face to driveway and back to driveway)and different heights(upper canopy and lower canopy)showed certain trends.The amount of dust-retention in face to driveway were bigger than it in back driveway.And the amount of dust-retention in lower canopy(2~5m)were bigger than it in upper canopy(5~7m).But the different directions and heights of canopy were no significant effect on the dust-retention of leaves,while the effect of the external environment also existed.(5)The difference of dust-retention capability of species were affected by many factors, including the factors about species itself and environment.Leaf characteristics affected the way of dust-retention directly so as to affect the dust-retention capability.The leaves of species which were rough and furrow remain conducive to dust-retention,and leaves which were glabrous were not conducive to dust-retention.Specific leaf weight and dust-retention capability of leaves were significantly correlated.The larger specific leaf weight of species,the amount of dust-retention were greater.The specific leaf weight affect the stability of dust-retention.With the dust of environment increased,the amount of dust-retention increasing.In suitable climate and environment conditions , the better growth of species , the stronger of environmental suitability.And then,they could able to show the better of dust-retention capability and ecological benefits.(6)During the content investigation on the seasonal photosynthetic indexes(including net photosynthetic rate,transpiration rate and stomatal conductance)and chlorophyll of keynote trees in Fuzhou and Xiamen,there are differences in the indexes among species.By principal component analysis,putting standardized original data into equation,and taking variance contribution for weight,comprehensive scores were obtained in photosynthetic characteristics of species.The superiority order of photosynthetic characteristics of keynote trees in Fuzhou as follows:Bauhinia blakeana > Cinnamomum camphora > Mangifera indica > Ficus microcarpa, while in Xiamen as follows:Bauhinia blakeana > Winchia calophylla > Ficus altissima > Mangifera indica.(7)On the comparison of daily variation of net photosynthetic rate(Pn),transpiration rate (Tr)and stomatal conductance(Gs)of keynote trees in Fuzhou and Xiamen,dusty leaves were lower than clean leaves obviously , and dust-retention does negative effects on the photosynthesis.Change range of one day was different with the variation of time and light between clean and dusty leaves.Generally speaking,the peak value loss of photosynthetic indexes about dusty leaves is maximum compared with clean leaves during one day.(8)Analyzed the loss rates of photosynthetic indexes and luminous energy use efficiency(LUE)of dusty leaves,the results showed that each specie had different loss rates (â–³Pn,â–³Tr,â–³Gs)of photosynthetic characteristics,and responsed to dust pollution also different.LUE of dusty leaves were lower than clean leaves,and the loss rate of LUE was different from each species,which reflected indirectly that different species have different pollution-resistant. (9)Analyzed and compared the differences of chlorophyll content of the same species between which growing in the dust polluted environmen(troad)and the clean environmen(tforest park),the mensuration results of keynote trees consistently showed that chlorophyll content (Ca+b)in the dust polluted environment is lower than that in the clean environment,however, the ratio between chlorophyll a and chlorophyll b(Ca/Cb)in the dust polluted environment is higher than that in the cleaner environment.(10)According to the differences of the increased proportion of the value Ca/Cb of different species,the pollution-resistant capability of species could be defined.The larger the increased proportion of the value Ca/Cb,the weaker the pollution-resistant capability of the species,and the opposite is true.The pollution-resistant capability of keynote trees in Fuzhou showed as followed: Ficus microcarpa > Cinnamomum camphora >Bauhinia blakeana > Mangifera indica,and in Xiamen as follows:Ficus altissima > Bauhinia blakeana > Mangifera indica > Winchia calophylla.