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题名: 硬化地表对城市幼树物候、生长和蒸腾的影响
作者: 陈媛媛
学位类别: 博士
答辩日期: 2016-05
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 王效科
关键词: 硬化地表,城市树木生长,物候期,光合特性,蒸腾,树干液流 ; pavements, tree growth, phenology, photosynthetic characteristics, transpiration, sap flow
其他题名: Responses of the phenology, growth and transpiration of urban sapling to pavements
学位专业: 生态学
中文摘要:     城市植物具有涵养水源、缓解热岛效应、净化空气和减少噪音等重要的生态服务功能,在维持城市生态平衡和改善城市生态环境方面发挥着重要的作用。然而,随着城市化进程的加速,硬化地表面积不断扩大,显著地改变了城市植物赖以生存的环境条件,进而影响了城市植物的正常生长和水分代谢过程。因此,研究城市植物生长和水分利用特征对不同硬化地表类型的响应机制,对于城市绿地规划、城市绿化树种选择、城市生态服务功能发挥、城市水资源利用效率的提高、以及科学合理的城市绿地管理制度的建立具有十分重要的意义。
    本研究通过建立较大面积的试验场模拟城市不同硬化地表类型(对照、透水硬化地表和不透水硬化地表),并设置不同种植密度(0.5 m、1.0 m 和2.0 m),对北京绿化树种(油松、白蜡和元宝枫)的生长过程、物候期、叶片光合特性、树干液流及环境因子等指标进行为期三年的连续同步观测。本研究通过分析不同硬化地表类型下油松、白蜡和元宝枫土壤微环境的差异、生长变化过程、叶片光合特性和蒸腾耗水以及树干液流的变化规律,探讨了不同硬化地表类型引起的土壤微环境改变对研究树种生长过程的影响,并在综合各研究结果的基础上对城市硬化地表类型的设置、绿化树种的选择和绿地健康管理提出科学合理的建议。主要研究结果如下:
    (1)硬化地表相比于对照极显著地提高了地表温度和土壤温度(P<0.01),且表现为透水地表>不透水地表>对照。在典型的晴朗天气条件下,透水地表和不透水地表日最高温度比对照分别提高10.68-16.05°C 和11.52-12.31°C,日平均地表温度比对照分别提高2.62-3.20°C 和0.52-3.04°C。透水地表和不透水地表下土壤温度日最高值比对照分别提高了6.67-10.02°C 和 4.07-8.42°C,平均土壤温度比对照分别提高了1.73-3.67°C 和2.04-3.37°C。在树木生长季,硬化地表显著提高地表温度,对油松和元宝枫生长形成长期高温环境,2013 年油松和元宝枫地表温度日最高值>40°C 的天数分别占整个生长季的35.3%(透水地表)和23.9%(不透水地表);2014 年地表温度日最高值>40°C 的天数相比于2013 年明显增多。相比于油松和元宝枫,白蜡冠幅较大,郁闭度高,在一定程度上能有效缓解硬化地表形成的高温环境。
    (2)不同地表类型对不同树种的土壤含水量影响存在差异。油松表现为透水地表>不透水地表>对照;白蜡表现为对照>透水地表>不透水地表;元宝枫表现为透水地表>对照>不透水地表。不透水地表由于降低了降水的下渗,导致土壤含水量降低,不透水地表上生长的白蜡长期处于干旱胁迫下。透水地表利于降水入渗,且在干旱少雨季节减少了土壤蒸发散失,在长期连续观测过程中相比于对照和不透水地表提高了土壤含水量。对照和不透水地表2014 年土壤含水量低于15%的天数多于2013 年。
    (3)硬化地表使得白蜡和元宝枫幼苗的发芽时间和秋季落叶时间显著提前。硬化地表上白蜡和元宝枫幼苗发芽时间分别比对照提前了0.7-9.3 天和0.3-2.3天,硬化地表对白蜡和元宝枫生长期的长短无显著影响。
    (4)硬化地表显著降低了油松净光合速率、气孔导度、蒸腾速率、叶绿素含量以及株高、基径的生长(P<0.05)。对照和透水地表上生长的白蜡光合参数、叶绿素含量、株高和基径的生长均高于不透水地表。2013 年硬化地表显著降低了元宝枫幼苗成活率、光合参数和叶绿素含量(P<0.05),破坏了叶片光系统结构,产生光抑制现象,抑制了株高和基径的生长;2014 年透水地表上生长的元宝枫光合特性及株高、基径年增长量高于对照和透水地表。
    (5)城市硬化地表温度过高,是抑制油松和元宝枫生长的主要因素。不透水地表土壤含水量降低是导致白蜡株高和基径下降的主要原因。对于元宝枫来说,2013 年透水地表过高的地表温度掩盖了土壤水分的有利条件,导致元宝枫生长显著低于不透水地表。随着元宝枫生长年限的延长,冠幅增大,缓解了硬化地表形成的高温环境,元宝枫生长对硬化地表产生了一定的适应性,透水地表形成的相对较高的土壤含水量逐渐体现出优势,元宝枫净光合速率逐渐升高,生长速率急剧增大。
    (6)硬化地表对不同树种树干液流速率和日累积量的影响有一定差异。不透水硬化地表上生长的油松树干液流速率和日累积量显著低于对照(P<0.05),透水和不透水硬化地表上生长的元宝枫树干液流速率和日累积量均显著低于对照(P<0.05)。硬化地表对白蜡树干液流速率和日累积量无显著影响。硬化地表抑制了油松和元宝枫的株高和树干直径的生长,油松和元宝枫树干液流与株高和树干直径具有显著的正相关关系。硬化地表上生长的油松和元宝枫树干液流减少的原因主要有:土壤含水量下降,直接影响根系吸水能力;硬化地表降低树木株高和树干直径,地上部分生物量减少,降低了水分需求量及吸水能力,导致树干液流速率下降。
    在配置和种植城市绿化植物时,为缓解硬化地表对城市树木生长发育的不利影响,应选择适应高温和干旱的植物,并采取降温和灌溉措施来降低硬化地表的影响。从植株生长对不同地表类型的响应差异来看,白蜡相比于油松和元宝枫可能更适宜作为绿化树种。
英文摘要:      Urban trees can provide many ecosystem services to help maintain the ecological balance, improve eco-environment conditions, and enhance the quality of life for residents. These include reducing stormwater flows by increasing rainfall interception, alleviating urban heat island effects through evaporative cooling and shade provision, improving air quality via absorption of gas and particulate pollutants, and reducing noise. However, with the accelerating of urbanization, the land surface is being transformed from vegetated landscapes into pavements in urban areas, such as roads, squares, parking lot. Urban pavements have profoundly changed the urban environment factors, hindering gas exchange between air and soil, and thereby affecting plant growth and water physiology. Studies on plant growth and water use characteristics of typical landscape tree species and its response to urban pavements environment are of great importance to urban green space planning, tree species selection, urban ecosystem services delivery, the improvement of water use efficiency, and ultimately the establishment of reasonable and scientific management regulations of urban green space.
    In this study, we investigated plant responses to pavement in the suburb of Changping District, Beijing. We planted the saplings of three common urban tree species, Pinus tabuliformis, Fraxinus chinensis, and Acer truncatum, in three different pavements (pervious brick pavement, impervious brick pavement, and no pavement as the control) at three different densities (0.5 m, 1.0 m and 2.0 m apart). We investigated the influences of different pavement types on soil micro-environments, plant growth and ecophysiology by monitoring surface temperature, soil temperature and soil moisture content (20 cm), as well as tree survival rate, height, basal diameter, photosynthetic parameters, phenological phases, and sap flow rate, from April 2012 to November 2015. By comparing the difference of soil micro-environments, plant growth, leaf photosynthetic characteristics, phenological phases, and water use efficiency, the objective of this study was to explore the effects of pavement-induced environmental changes on plant growth and water physiology, and give suggestions
on urban green space construction and management. The main conclusions are as followed:
    (1) Pavements had significantly higher surface temperature and soil temperature than the control (P<0.01), with a higher surface temperature noted for the pervious pavement than for the impervious pavement. In typical sunny conditions, daily maximum surface temperature increased by 10.68-16.05°C and 11.52-12.31°C under pervious pavement and impervious pavement compared to the control, respectively. Diurnal mean surface temperature increased by 2.62-3.20°C and 0.52-3.04°C under pervious pavement and impervious pavement compared to the control, respectively. Daily maximum soil temperature increased by 6.67-10.02°C and 4.07-8.42°C under pervious pavement and impervious pavement compared to the control, respectively. Diurnal mean soil temperature increased by 1.73-3.67°C and 2.04-3.37°C under pervious pavement and impervious pavement compared to the control, respectively. Daily maximum and diurnal mean surface temperatures under pervious pavement increased by 3.34-7.45°C and 0.16-2.72°C compared to impervious pavement, respectively. Daily maximum soil temperatures under pervious pavement increased by 1.60-2.60°C compared to impervious pavement. Throughout tree growing seasons, pavements had significantly higher surface temperature than the control, leading to
long-term high-temperature environment for Pinus tabuliformis and Acer truncatum (>40°C). For Pinus tabuliformis and Acer truncatum, the total number of days with maximum value of surface temperature exceeding 40°C accounted for 35.3% (pervious pavement) and 23.9% (impervious pavement) of the entire growing period in 2013. The total number of days with maximum value of surface temperature exceeding 40°C was greater in year 2014 than in year 2013. Compared to Pinus tabuliformis and Acer truncatum, Fraxinus chinensis had larger canopy density, which could effectively mitigate the pavement induced high-temperature environment to a certain degree.
    (2) The response of soil moisture to pavements varied with tree species. For Pinus tabuliformis, soil moisture content was greater in pavements than in the control, with greater soil moisture noted for pervious pavment than for the impervious pavement. For Fraxinus chinensis, soil moisture was greater in control than the pavements, with greater soil moisture noted for pervious pavment than for the impervious pavement. For Acer truncatum, soil moisture was ranked from highest to lowest as: pervious pavement, control, impervious pavement. Due to the reduction in precipitation infiltration, soil moisture significantly reduced under impervious pavement, causing long-term drought stress for Fraxinus chinensis growth. Pervious pavement can improve soil moisture compared to control and impervious pavement by increasing rainfall infiltration, and decreasing soil evaporation loss in drought seasons. The total number of days with soil moisture less than 15% was greater in year 2014 than in year 2013.
    (3) Dates of leaf budburst and senescence for Fraxinus chinensis and Acer truncatum significantly advanced under pavements compared to the control. The date of full leaf budburst was earlier by 0.7-9.3 d for Fraxinus chinensis and by 0.3-2.3 d for Acer truncatum under pavements than the control, respectively. Pavements had no significant influence on the growing periods.
    (4) For Pinus tabulaeformis, pavements induced heat stress led to the significant decrease in net photosynthetic rate, stomatal conductance, transpiration rate, leaf chlorophyll content, and, subsequently, a decrease in tree height and basal diameter (P<0.05). For Fraxinus chinensis, impervious pavement induced drought stress led to the decrease in photosynthetic parameters, leaf chlorophyll content, and tree height and basal diameter compared to the pervious pavement and the control. For Acer truncatum, pavements induced heat stress led to the significant decrease in sapling survival rate, photosynthetic parameters, and leaf chlorophyll content in year 2013. Acer truncatum saplings under pavements cannot use all the excess of light energy for photosynthesis, increasing the susceptibility of plants to photoinhibition in year 2013. As a consequence, tree height and basal diameter of Acer truncatum decreased under pavements compared to the control in year 2013. In year 2014, the photosynthetic parameters, and increment of tree height and basal diameter of Acer truncatum were greater under pervious pavement compared to the control and the impervious pavement.
     (5) For Pinus tabulaeformis and Acer truncatum, pavement induced heat stress is the main factor inhibiting growth. For Fraxinus chinensis, impervious pavement induced drought stress is the main factor leading to the decrease of tree height and basal diameter. For Acer truncatum, the favorable conditions of soil moisture under pervious pavement were covered by the excessive high surface temperature in 2013, leading to the significant decrease of growth under pervious pavement compared to the impervious pavement. As the tree age increased, the increasing canopy density of Acer truncatum could help alleviate the heat stress environment induced by pavements, and promote adaptation to the heat stress environment. Since pervious pavement had relatively higher soil moisture compared to the impervious pavement and the control, net photosynthesis rate gradually advanced, leading to the increase inAcer truncatum growth.
    (6) The responses of sap flow rate and sap flow flux of Pinus tabulaeformis, Fraxinus chinensis, and Acer truncatum to pavements are different. In sunshine weather, sap flow rate and sap flow flux of Pinus tabulaeformis were significantly lower in the impervious pavement treatment than in the control treatment, and sap flow rate and sap flow flux of Acer truncatum were significantly lower in the pavement treatments than in the control treatment (P<0.05). There were no significant differences among three different types of pavements for Fraxinus chinensis. Surface temperature was higher, and soil moisture content was lower in the pavement treatments than in the control, inhibiting the growth of tree height and stem diameter.There was a significant positive correlation for sap flow flux between tree height and
stem diameter for Pinus tabulaeformis (P<0.01) and Acer truncatum (P<0.05). Due to the increase in surface temperature and decrease in soil moisture content, and consequently the decrease in tree height and stem diameter under pavements, the corresponding water use demand and transport capacity would directly influence the sap flow rate and sap flow flux of Pinus tabulaeformis and Acer truncatum.
    Therefore, it is necessary to select heat and drought tolerant tree species, and manage land with shadowing or irrigation, in order to guarantee tree growth in paved urban environments. Based on the response of three tree species growth to different types of pavements, Fraxinus chinensis could be more appropriate for greening tree species than Pinus tabulaeformis and Acer truncatum.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/36781
Appears in Collections:城市与区域生态国家重点实验室_学位论文

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Recommended Citation:
陈媛媛. 硬化地表对城市幼树物候、生长和蒸腾的影响[D]. 北京. 中国科学院研究生院. 2016.
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