广州城郊环境梯度下马尾松针叶元素质量分数变化特征

城市化、工业化迅速发展及人类活动的加剧给城市及其周边地区森林生态系统带来前所未有的干扰和压力。植物冠层是植物与大气直接进行气体交换的界面,冠层叶组织化学分析已成为评价环境污染对森林树木健康的影响,指示环境污染的有效手段。文章以广州黄埔工业区(丹水坑风景区)、城郊接壤区(华南植物园)和近郊(帽峰山森林公园)这一环境梯度为对象,在各研究点上选定自然生长的、成熟健康的马尾松(Pinus massonianaL.)5株,分别采集树冠中部向阳枝条上的当年生(Current,C)和一年生(Current 1,C 1)针叶,然后将每组针叶区分为带叶鞘针叶、去叶鞘针叶和叶鞘3个组分进行样本制备,测定N、Al、Cu、Cd、Pb、Zn、Cr、Ni元素质量分数,旨在探讨利用马尾松针叶不同组分的元素质量分数用于指示城郊梯度环境质量变化的适宜性和可靠性。研究结果表明:①当年生带叶鞘针叶中Al质量分数显著高于当年生去叶鞘针叶(p<0.05),其余元素在当年生和一年生的去叶鞘针叶与带叶鞘的完整针叶间均无显著差异;②Ni在当年生针叶及其叶鞘间没有显著差异(p<0.05),其它被测定的金属元素无论在当年生还是一年生针叶中,均表现为叶鞘中的元素质量分数均显著高于去叶鞘针叶(p<0.05),体现了针叶与叶鞘在形态结构上的差异引起重金属积累的差异;而非金属元素N质量分数则针叶显著高于叶鞘;③一年生针叶中Ni质量分数显著低于当年生针叶,但Al、Pb、Zn质量分数显著高于当年生针叶,一年生叶鞘中所有金属元素的质量分数都显著高于当年生叶鞘,表现出随暴露时间和针叶寿命的延长而持续累积的特征;而营养元素N质量分数在当年生针叶和一年生针叶以及当年生叶鞘和一年生叶鞘间无显著差异;④城乡环境梯度下生长的马尾松为研究环境质量演变提供了一个天然的实验室,受人类活动干扰大的城区马尾松一年生针叶的Cd和N质量分数及其叶鞘中的Cu、Cr、Ni质量分数显著高于受人为干扰较少的郊区,表明植物组织中元素化学特征反映了城市发展过程中人类活动的足迹。在城市环境尤其是重金属污染的监测中,成熟的一年生叶鞘更具指示意义,效果更显著。

Variations of concentrations of elements in needles of Pinus massoniana(L.)along an urban-suburban gradient in Guangzhou

Increasing urbanization, industralization along with human activities have imposed unprecedented disturbance and suppression on urban forest ecosystems and their surrounding areas. Canopy serves as the active interface for gas exchange of trees with the environment, and chemical assay of foliage has been frequently and extensively employed as the useful tool for forest health risk assessment and environmental monitoring and bioindication. In the present study, we selected Huangpu, Botannical Garden, and Maofengshan as the representative site of the industrial center of Guangzhou, urban-suburban transition, and suburban area, respec- tively. Five mature, health-looking pines (Pinus massoniana (L.)) grown in field at each site were sampled. The current (C) and previous year(C 1) needles were collected from branches of each tree at the mid crown, and pooled by needle age. The needles with the same age were separated into three parts including needles attached with sheath, needles without sheath and needle sheath. Concentrations of total N, Al, Cu, Cd, Pb, Zn, Cr and Ni for all components of needles were determined to elucidate the suitability and reliability of pine needles in monitoring urban-suburban environmental change. The results were as follows, 1) The C needles with sheaths had significantly higher concentration of Al than those without sheaths, but this difference was not observed for other elements either in the C needles or the C 1 needles. 2) The sheaths for both needle ages had significantly higher concentrations of all metal elements than needles without sheaths, with the exception for Ni, suggesting the extant difference in metal accumulation rate caused by the dissimilarity in morphological and anatomical aspects between the bared needles and the sheaths; however, needles of both ages had significantly higher concentrations of nitrogen than those of needle sheaths. 3) Nickel concentration in the C 1 needles was lower, while Al, Pb and Zn concentrations were higher than those in the C needles. Concentrations of all the metal elements in the C 1 needle sheaths were significantly higher than the C needle sheaths, demonstrating that accumulation of metal elements increased with prolonged exposure time and needle longevity; however, the nutritional nitrogen concentration did not show significant relations with needle age. 4) Masson pine growing along the ur- ban-suburban gradient provided a natural laboratory for environmental quality study, Cd and N concentrations in C 1 needles as well as Cu, Cr, Ni concentrations in their sheaths collected from highly human-impacted Guangzhou were significantly higher than its suburban Maofeng mountain, reflecting the ecological footprints of the anthropogenic activities along the urbanization course. 5) Among all the needle components divided and tested, the C 1 needle sheath is the best bioindicator for environmental monitoring, particularly efficient for heavy metal pollution assessment.