淮南市6种典型行道树叶片富集多环芳烃(PAHs)的差异研究

Study on the Difference of Enrichment of Polycyclic Aromatic Hydrocarbons by Leaves of Six Typical Species of Roadside Trees in Huainan Urban District

为揭示不同行道树的叶蜡、叶肉组织在不同交通流量下富集不同种类多环芳烃(PAHs)的差异及叶蜡与其中PAHs含量、气孔密度与叶肉组织中PAHs的相关性,在淮南市3个交通流量不同的主干道国庆中路(GQ,每分钟车流量60～65辆)、洞山西路(DS,每分钟车流量40～45辆)、淮河大道(HH,每分钟车流量10～25辆)分别采集了女贞(Ligustrum lucidum)、广玉兰(Magnolia grandiflora)、石楠(Photinia fraseri)、香樟(Cinnamomum camphora)、红叶李(Prunus cerasifera)和银杏(Ginkgo biloba)6种树木当年生枝条叶片120枚。同种树木的胸径、株高和叶面积相近。利用高效液相色谱仪测定了叶片叶蜡和叶肉中萘、芴、菲、荧蒽、芘、苯并(a)蒽、苯并(b)荧蒽、苯并(a)芘等8种PAHs含量,并应用显微镜的物镜测微尺计算叶片的气孔密度。结果表明,在相同的交通状况下,4种常绿树木叶蜡中2～5环PAHs的含量多数高于落叶树种,其中香樟叶蜡中2～4环PAHs(NAP、FLU、PHE、FLT、BaA)及女贞、广玉兰叶蜡中4～5环PAHs(PYR、Bb F、BaP)的含量最多。在国庆中路,这8种PAHs的检测值分别达到1 180、527、1 230、945、540、1 839、910、2 027 ng·g-1,为红叶李叶蜡中相应PAHs富集量的2.5～11.8倍。叶肉组织中PAHs的富集量虽然总体上低于叶蜡,但广玉兰、香樟和女贞叶肉中PAHs的富集量依然较高。在上述3种交通状况下,同种树木的叶肉和叶蜡对PAHs的富集量之间差异显著,表现为国庆中路>洞山西路>淮河大道趋势。同时,6种行道树叶蜡含量与叶蜡富集PAHs总量之间、气孔密度与叶肉组织PAHs总量之间均呈显著正相关(P<0.05),且相关系数随着交通流量的增大而升高。因此,在交通流量大的市区,以常绿树木为主要行道树有利于消减大气中PAHs污染。

In order to investigate the difference of the enrichment of different polycyclic aromatic hydrocarbons(PAHs)in wax or mesophyll tissues of leaves in different roadside trees under different traffic flow,and analyze the correlation of the contents of PAHs in leaf wax with contents of leaf wax as well as the correlation of stomatal densities with PAHs accumulation in mesophyll tissues,120 leaves were randomly sampled in current-year branches of each of the roadside trees i.e.L.lucidum,M.grandiflora,P.fraseri,C.camphora,P.cerasifera,and G.biloba grown in Guoqing Middle Road(GQ,60-65 cars per minute),Dongshan West Road(DS,40-45 cars per minute),and Huaihe Avenues(HH,10-25 cars per minute)in Huainan urban area,respectively.Chest diameter,height or leaf area was similar in the same species of trees.HPLC was employed to measure the contents of naphthalene(NAP),fluorene(FLU),phenanthrene(PHE),fluoranthene(FLT),pyrene(PYR),benzo(a)anthracene(BaA),benzo(b)fluoranthene(BbF),and benzo(a)pyrene(BaP)in the wax or mesophyll tissues of leaves.Besides,the stomatal densities of leaves were also determined by micrometer under microscope.The results showed that the contents of PAHs with 2-5 circles in leaf wax of four species of evergreen trees were more than those in deciduous trees under the same traffic conditions.Of which,the contents of PAHs with 2-4 circles(i.e.NAP,FLU,PHE,FLT and BaA)in leaf wax of C.camphora and the contents of PAHs with 4-5 circles(i.e.PYR,BbF and BaP)in wax of L.lucidum and M.grandiflora were the most.In GQ area,the values of these eight PAHs mentioned above were 1 180,527,1 230,945,540,1 839,910,and 2 027 ng·g-1 respectively,which were up to be 2.5-11.8 times of the corresponding PAHs in leaf wax of P.cerasifera.In general,the PAHs enriched in the mesophyllous tissues were less than those in the leaf wax.However,these PAHs remained higher in the mesophyll tissues of M.grandiflora,C.camphora and L.lucidum.Under the three traffic conditions,significant difference exhibited in the enrichment of PAHs by the mesophyll or leaf wax in the same species of trees,indicating thatGQ>DS>HH.Moreover,significantly positive correlation could not only be found between the amount of leaf wax and the total of PAHs enriched by the wax,but also be showed between the stomatal densities and the total PAHs accumulated in the mesophyllous tissues in all the six species of roadside trees(P<0.05).In addition,the correlation coefficients increased with the increase of the traffic flow in the urban areas.As a result,it can be suggested that evergreen trees should be employed as main roadside trees to reduce the pollution by PAHs in urban districts with higher traffic flow.