典型城区与郊区环境大叶黄杨气体交换及叶绿素荧光特性比较

Comparative analysis of leaf gas exchange and chlorophyll fluorescence of Euonymus japonicus Thunb by field experiment in the typical urban and suburban areas in Beijing

采用Li-6400便携式光合作用测定系统对夏秋季典型城区与郊区环境下大叶黄杨的气体交换和叶绿素荧光特性进行了现场实验比较研究。研究显示,叶片净光合速率的大小由总光合速率(光合能力)和呼吸速率共同决定,城区环境温度较高、相对湿度较低、大气CO2浓度较高,不同月份城区和郊区样点大叶黄杨的净光合速率差异显著性存在不同。城区环境下大叶黄杨的胞间CO2浓度、叶面水气压亏缺、蒸腾速率高于郊区环境。城区环境中温度、大气CO2浓度等的变化会影响叶片呼吸作用,造成呼吸速率升高或是降低,城区环境中污染物浓度变化也会损伤叶片光合结构从而导致总光合能力降低,这两者都会引起净光合速率的变化。通过大叶黄杨叶片叶绿素荧光指标的进一步对比分析发现,城区大叶黄杨叶片叶绿素总量、叶绿素a/b、Fv/Fm、Fv/Fo、qP、ΦPSⅡ、ETR降低,但qN升高。表明叶片叶绿体PSⅡ的功能受到负面影响。城区大叶黄杨叶片荧光参数的变化,从微观机制上表明城区环境中污染物浓度的上升导致叶绿素及叶绿体光合结构受损的确是叶片光合能力下降的主要原因之一。

Using Li-6400 portable photosynthesis system, we studied the differences of leaf gas exchange and chlorophyll fluorescence of Euonymus japonicus Thunb by the field experiment in summer and autumn seasons in the typical urban and suburban areas in Beijing city. The results showed that there are higher levels of atmospheric temperature, relative humidity and CO2 concentration in the urban areas than that in the suburban areas, the net assimilation ability of CO2 for E. japonicus leaf is usually subject to the total assimilation ability of CO2 and respiration rate, and its significances of difference varied in the studied months. In addition, the indicators of intercellular CO2 concentration, VPDleaf-to-air, transpiration rate of E. japonicus leaf in the urban plot were higher than those in the suburban plot. The monthly changes in atmospheric temperature and CO2 concentration in the urban areas affected leaf respiration, leading to a increase or decrease of leaf respiration rate, concentration also damaged chlorophyll and chloroplast assimilation ability of CO2, both of them determined the in the same time, the monthly changes in atmospheric pollutants＇ of E. japonicus leaf and further led to the decline in its total variation in net assimilation ability of CO2 for E. japonicus leaf. Further comparative analysis of leaf chlorophyll fluorescence parameters indicated that, the total content of chlorophyll, chlorophyll a/b and chlorophyll fluorescence parameters （ Fv/Fm, Fv/Fo, qP, φPS Ⅱ , ETR） for E. japonicus leaf in the urban plot decreased but qN increased, showing that the activity of leaf photosystem Ⅱ was negatively affected by the increase in atmospheric pollutants＇ concentration and led to the damage to chlorophyll and chloroplast of E. japonicus leaf that really became a cause for the reduction of leaf total assimilation ability of CO2 in the urban areas.