北京地区4种阔叶树光合作用对CO2浓度及温度变化的响应

为探讨植物对CO2浓度和温度组合变化的生态响应,在植物生长旺季,对北京地区银杏、杜仲、玉兰和华东椴4个树种叶片光合特性进行了研究。结果表明:4个树种的光合最适温在30℃左右,夏季晴天的持续高温(>30℃)不利于4个树种光合作用。在CO2浓度加倍条件下,4个树种的光合速率明显增大,但银杏和杜仲的光合最适温并未升高,玉兰则升高了2℃,华东椴升高了4℃。可以预测,未来大气CO2浓度加倍导致气温升高,对银杏和杜仲光合作用的抑制作用将加强,玉兰和华东椴将得到缓解。水汽压亏缺(VPD)对温度变化敏感,而气孔对VPD十分敏感,温度升高时,VPD增大引起气孔导度(Gs)减小,会限制叶片对外界CO2的吸收,这可能是高温限制植物光合作用的原因之一。在相同的温度条件下,CO2浓度加倍,4个树种的Gs值均有所降低。

Photosynthesis response to variation of CO2 concentration and temperature of four broad-leaved trees in Beijing region

In peak growing season,the photosynthetic characteristic of Ginkgo biloba,Eucommia ulmoides,Magnolia denudata and Tilia japonica were measured for discussing the photosynthesis response to variation of CO_2 concentration and temperature.The results showed that the ambient CO_2 concentration could not satisfy the demand of these four species' photosynthesis,and their optimal temperatures for photosynthesis were lower than the average daytime air temperature,hence the photosynthesis of these four species were restricted by lower CO_2 concentration and higher daytime air temperature at the present time.Remarkable enhancement in the net photosynthetic rate at doubled CO_2 concentration were found in all the four species.When the dependency on CO_2 and temperature were examined simultaneously,it was seen that for the elevated CO_2 concentration there was a shift in the optimum temperature for Magnolia denudata and Tila japonica towards higher temperatures.Due to its independence on CO_2 concentration,this trend could not be found in the Ginkgo biloba and Eucommia ulmoides data set.The stomatal conductance(Gs) was sensitive to vapor pressure deficit(VPD) and the VPD was sensitive to temperature.An increase in temperature would cause the VPD to increase,and plants might be assumed to react by reducing their stomatal apertures,the effect on stomatal resistance would be most significant at high temperatures.The restriction to stomatal for this four species would be enhanced when CO_2 concentration were elevated at same temperature.