Diurnal and seasonal fluctuation in ambient CO2 concentration (C^) of more than 100 cm^ m‘3 in urban areas is an important abiotic factor influencing photosynthetic activity. This was shown in a young poplar tree under controlled environmental conditions. Here, the short-term rise in from 320 to 360 cm^ m‘3 during a day resulted in a 10 % higher CO2 gain. This variation in also influenced the interpretation of CO2 exchange data. Calculation of the intemal CO2 concentration in a leaf, Q, on the basis of an assumed mean value of atmospheric CO2 of 340 cm^ m'^ led to a possible 8 % divergence ffom the actual Cj in our experiments and thus also to a falše interpretation of the results, as it concealed the photosynthetic response to a rise or decline of Cg. Additionally, the changing CO2 concentration directly influenced the measurement by the infrared gas analyzer, because of its nonlinear response. Lack of compensation for this can lead to an additional inaccuracy of 3 to 8 % in the calculation of net photosynthetic rate and Q.
The effects of varying leaf temperature (T1) on some ecophysiological characteristics of photosynthesis for Quercus liaotungensis Koiz. under ambient radiation stress around midday on clear summer days were investigated using an IRGA equipped with a temperature-controlled cuvette. Net photosynthetic rate (PN) decreased as T1 increased from 30 to 35 °C as a result of stomatal closure, whereas non-stomatal limitation led to decreased PN in the T1 range of 35-45 °C. Decreased transpiration rate (E) and stomatal conductance (gs) at leaf temperatures above 30 °C were interpreted as a combined 'feedward' effect as a result of enhanced leaf-air vapour pressure deficit (VPD) and stomatal closure. Changes in E from T1 30 to 20 °C depended on VPD when gs was maintained constant. Water use efficiency (WUE) varied inversely with T1 by following a hyperbola. A decrease in intercellular CO2 concentration (Ci) occurred as a result of stomatal closure and a relatively high carboxylation capacity, whereas inactivation of mesophyll carboxylation in combination with photorespiration might be associated with the observed increase in Ci in the T1 range of 40 to 45 °C. and Shouren Zhang ... [et al.].