北京典型绿化树种幼苗光合特性对硬化地表的响应

Effect of pavement on the leaf photosynthetic characteristics of saplings of three common tree species(Pinus tabulaeformis,Fraxinus chinensis,and Acer truncatum) in Beijing

以北京典型绿化树种油松(Pinus tabulaeformis)、白蜡(Fraxinus chinensis)和元宝枫(Acer truncatum)幼苗为试验材料,设置透水硬化地表、不透水硬化地表和对照3个水平的地表类型,通过监测地表温度、土壤含水量(20 cm)和光合参数等指标,分析3种树木叶片光合特性对硬化地表的响应特征。结果表明:城市硬化地表极显著地提高了地表温度(P<0.01),表现为透水地表>不透水地表>对照;不透水地表极显著地降低了3种树木土壤含水量(P<0.01);透水地表极显著地提高了油松和元宝枫土壤含水量(P<0.01)。两种硬化地表下油松、元宝枫和不透水地表下白蜡幼苗叶片的净光合速率、蒸腾速率和气孔导度降低,株高和基径生长受到抑制。硬化地表对油松和元宝枫的影响主要源于硬化地表形成的高温胁迫,对白蜡的影响主要源于不透水地表形成的干旱胁迫。因此,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。

Pavement is one of the most important factors causing environmental changes in urban areas. In this study, saplings of three common tree species （ pine, Pinus tabulaeformis ; ash, Fraxinus chinensis ; and maple, Acer truncatum） were planted in three different treatment plots： pervious brick pavement with a permeability coefficient of more than 0.4 mm/s, impervious brick pavement with a permeability coefficient near zero, and non-pavement （control）. In response to the pavement treatments, leaf photosynthetic characteristics of the pine, ash, and maple trees were determined by measuring surface temperature, soil moisture content （20 cm）, and photosynthetic parameters. The results showed that surface temperature was significantly higher in the pavement treatments than in the control treatment （P〈0.01）, with a higher surface temperature noted for the pervious pavement than for the impervious pavement. For all the tree species （especially ash）, soil moisture content was significantly lower in the impervious pavement treatment than in the pervious pavement and control treatments （P〈 0.01 ）. Soil moisture content was significantly higher for pine and maple in the pervious pavement treatment than in the impervious pavement and control treatments （P〈0.01）. For pine and maple, the total number of days with a maximum surface temperature exceeding 40℃ accounted for 53.3% （pervious pavement treatment） and 36.1% （impervious pavement treatment） of the entire growing period. For ash, the total number of days with daily mean soil moisture content less than 15% accounted for 88.5% （impervious pavement treatment） of the entire growing period. The pavement caused heat stress on pine and maple growth, and the impervious pavement caused drought stress on ash growth, leading to a decrease in net photosynthetic rate, transpiration rate, and stomatal conductance, and, subsequently, a decrease in tree height and basal diameter. For pine, significantly lower tree height （ 12.6% and 18.5%） and basal diameter （18.5% and 17.1%） were noted for the pervious and impervious pavement treatments, respectively, than for the control treatment. For maple, significantly lower tree height （45.1% and 26.8%） and basal diameter （40.9% and 20.3% ） were noted for the pervious and impervious pavement treatments, respectively, than for the control treatment. For ash, significantly lower tree height （11.1% and 14.6%） and basal diameter （9.4% and 11.3%） were noted for the impervious pavement treatment, than for the pervious pavement and control treatments. In conclusion, 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.