城区土壤环境氮素和水分变化对火炬树光合生理生态的影响

Effects of Urban Soil Nitrogen and Moisture Changes on Photosynthetic Eco-physiological Processes of Rhus typhina

采用盆栽模拟研究了城市居民区绿地、城区道路绿化带与郊区林地3种土壤类型下的氮素及水分变化对火炬树光合生理生态的影响。随郊区-城区土壤水分含量的减少,火炬树的光合速率、气孔导度、细胞间CO2浓度和蒸腾速率呈明显的下降趋势,而叶片水汽压亏缺增大,不同水分条件下,光合参数变化的幅度不同。在城区较低氮素水平下,随水分含量的下降,火炬树光合速率下降的主要限制因子由气孔限制转变为非气孔限制,表明其叶绿体结构已经受到了破坏。在郊区较高氮素水平下,火炬树叶片的光合速率、气孔导度、细胞间CO2浓度等光合生理指标与城区相比,都有所增加,但蒸腾速率增加的幅度较小,因而水分利用效率也有所提高。随土壤水分的降低,叶绿素a、叶绿素b与叶绿素a+b含量都呈下降趋势;在城区氮素水平下,叶绿素a、叶绿素b与叶绿素a+b的含量与郊区比有显著的降低。

Through the comparative experiments of simulated soil environment, the influences of the changes of soil nitrogen and moisture on the photosynthetic, physiological and ecological activities of Rhus typhina＇s were examined with three different kinds of soils： suburban forest land, green spaces in urban residential area, and road greenbelts. Along with the decrease of soil moisture （from suburban soil to urban soil）, the photosynthesis rate （Pn）, stomata conductance （Gs）, transpiration rate （Tr） and intercellular CO2 concentration （Ci） of R. typhina decreased, but the VPD leaf-to-air increased. The variation scopes of gas exchange parameter during photosynthesis were different under different soil moisture conditions. Under the low nitrogen level in the urban area, with the decline of moisture content, the main limiting factor which affected the R. typhina photosynthesis rate gradually changed from stomata to non-stomata limitation, indicating that the R. typhina chloroplast structure was already destructed. While in the suburban areas, Pn, Gs, and Ci increased remarkably compared with the urban level, but Tr increased significantly, which indicated that the water use efficiency of R. typhina also improved. Along with the reduction of simulated moisture content, the content of chlorophyll a, chlorophyll b and chlorophyll a＋b dropped. In the urban nitrogen level, the content of chlorophyll a, chlorophyll b and the chlorophyll aH-b have reduced remarkably compared with the suburban areas.