元宝枫幼苗生长和光合特性对硬化地表的响应

Responses of growth and photosynthetic characteristics of Acer truncatum seedlings to hardening pavements

以北京典型绿化树种元宝枫(Acer truncatum)幼苗为试验对象,设置透水硬化地表、不透水硬化地表和对照(自然地表)3种地表类型,分析了元宝枫幼苗主要生理生态指标和生长指标对硬化地表的响应特征。结果表明:相比于对照,2种硬化地表引起地表温度显著升高,元宝枫幼苗叶片净光合速率(Pn)、气孔导度(gs)、蒸腾速率(Tr)、光合色素含量、光系统II光化学有效量子产量(Fv'/Fm')、PSII实际光量子效率(ФPSII)、光合电子传递速率(ETR)、光化学猝灭系数(qp)及最大净光合速率(Pmax)、表观量子效率(AQY)和光饱和点(LSP)均下降,叶片丙二醛(MDA)含量增加,株高和基径降低。硬化地表引起地表温度升高,对元宝枫幼苗生长造成了热胁迫,严重伤害了植物光系统II,光合电子传递被限制,减少了植物叶片的光合作用,抑制了植物生长。与不透水地表相比,透水地表粗糙度和孔隙度较高,增加了透水地表的热储存和热传导能力,地表温度显著升高形成的热胁迫对植物的生理伤害和生长影响更大。因此,在城市建设中,应考虑降低硬化地表的温度,以缓解城市绿化树种可能受到的热胁迫。

In this paper we investigated the ecophysiological characteristics and growth of Acer truncatum seedlings under different land pavements in a field experiment in a suburb of Beijing. A. truncatum seedlings were planted in different plots： paved with pervious bricks, paved with impervious brick, and non-paved （the control）. The results showed that pavement induced de- creases in net photosynthesis （ Pn ） , stomatal conductance （ gs ） , transpiration rate （ Tr ）, leaf photosynthetic pigment contents, photochemical effective quantum yield of photosystem II （Fv＇/ Fm＇）, actual photochemical efficiency （ФPSII）, electron transport rate （ETR）, photochemical quenching （ qp）, maximum net photosynthesis rate （ Pmax ） , apparent quantum yield （AQY） and light saturation point （LSP）, and enhanced MDA content. We also found that plant height and basal diameter of A. truncatum seedlings under pavements were reduced. Both pavements had sig- nificantly higher surface temperatures than the control, which resulted in heat stress on A. trunca- turn seedlings. The heat stress seriously hurt the photosystem II and limited the ETR, thus reduc- ing leaf photosynthesis and suppressing plant growth. Furthermore, pervious pavement had higher surface temperatures because it had higher roughness and heat storage capacity than impervious pavement. The ecophysiology and growth of A. truncatum seedlings would suffer more severe stres- ses under pervious pavement than under impervious pavement. This study highlights the impor-tance of urban greening for lowering surface temperatures of paved lands to alleviate heat stress due to pavements, especially pervious pavement.