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The Research between Leaf Anatomy and Polycyclic Aromatic Hydrocarbons Accumulation in Four Urban Steet Tree Species

Author: PengGang
Tutor: TianDaLun
School: Central South University of Forestry Science and Technology
Course: Ecology
Keywords: Urban tree species environmental pollution PAHs concentration leaf anatomy leaf structure leaf morphology Changsha city Hunan province
CLC: S718.4
Type: Master's thesis
Year: 2010
Downloads: 23
Quote: 0
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Abstract


Polycyclic Aromatic Hydrocarbons (PAHs) are a group of chemical compounds that consist of fused two or more benzene rings interconnected with each other by angular, linear and cluster means. Besides occurring naturally in coal, crude oil and gasoline, PAHs are also produced by incomplete combustion of coal, gasoline, wood, garbage or other organic materials. PAHs are lipophilic and widely distributed in the environment. As a pollutant, they are of concern because some compounds have been identified as carcinogenic, mutagenic, and teratogenic, which have great harmful effects on plants, animals and human health.Urban tree species are an important component of urban forest ecosystems, and play critical role in air purification in the urban environment. Usually, the leaves of urban tree species have strong capacity to absorb and accumulate PAHs, mainly expressed in the enrichment on gaseous and particulate PAHs. As a consequence, careful selection, intensive cultivation and better management of urban tree species have become one of the main subjects of building modern cities in terms of improvement of urban environment.In this study, the composition and accumulation of PAHs in leaves of four major urban street tree species (Cinnamomu camphora, Magnolia grandiflora, Opsmanthus fragrans and Redrlowered loropetalum) were investigated using Agilent 6890GC/5973MS in Changsha city, Hunan province. Structural features of the leaves, including leaf stomatal density, stomatal length:width ratio, leaf width:length ratio, and leaf area, were also measured. The aim of the project is to examine the relationship between PAHs concentration and surface structures of leaves of the four urban street tree species.The results showed that the concentration of total PAHs in the leaves of the four tree species ranged from 0.987 mg·kg-1 to 11.522mg·kg-1, with the mean of 4.513,3.540,2.798, and 3.992 mg·kg-1 for Cinnamomu camphora, Opsmanthus fragrans, Magnolia grandiflora, and Redrlowered loropetalum, respectively. PAHs concentrations in leaves of Cinnamomum camphora were significantly higher than that of Opsmanthus fragrans and Magnolia grandiflora. The total concentrations of PAHs were significantly lower in May than in January for the four urban street tree species, and the total concentrations of PAHs were statistically higher in the winter than in the spring for the four tree species of Cinnamomum camphora, Magnolia grandiflora, and Redrlowered loropetalum.It was found that 3-and 4-ring PAHs are the major parts of the total PAHs in the leaves regardless to the species and sampled seasons, which accounted for more than 75% of the total. The 5-and 6-ring PAHs accounted for less than 13% of the total, and 6-ring PAHs were below 4% of total. The adsorption of low-ring PAHs in the leaves was greater than high-ring PAHs. All 16 priority PAHs were detected in the leaves, except for the high-ring PAHs in Opsmanthus fragrans and Magnolia grandiflora during the spring season. All 16 PAHs were not evenly distributed in the leaves, and the Phe had the highest concentration for the four tree species in the study period.There were tightly relationships between leaf anatomical structures and the PAHs concentrations for the tree species. The palisade tissue thickness, spongy tissue thickness and the total leaf thickness were negatively correlated with the PAHs concentrations, while other structural features of the leaves were not sensitive to the changes in PAHs concentrations.Specifically, PAHs concentrations of Cinnamomum camphora increased with increasing of palisade tissue thickness, stomatal width and the ratio of palisade to spongy tissues, but decreased with the increases of the spongy tissue and the ratio of leaf width to length. The PAHs contents of Opsmanthus fragrans leaves decreased with increasing of the ratio of palisade to spongy tissues. For species Magnolia grandiflora, the PAHs concentrations increased with the increases of palisade tissue thickness, ration of palisade to spongy tissues, total leaf thickness, stomatal length and stomatal width. The concentrations of PAHs in Red Loropetalum leaves increased with increasing of cuticle thickness, spongy tissue thickness, leaf thickness and ratio of stomatal length to its width, but decreased with the increases of stomatal density and leaf area.The present study revealed the relationships between PAHs levels and leaf anatomical features of four urban greening tree species. The results indicated that structural characteristics of leaves of urban tree species were important factors in affecting the accumulation of PAHs in study area. The study not only provided the first-hand data and information regarding to the PAHs levels in different tree species and transmission path of PAHs in the environment, but also provided scientific references for selection and management of urban greening tree species.

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CLC: > Agricultural Sciences > Forestry > Forestry basic science > Forest Biology > Dendrology
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