Photosynthetic responses of Quercus fabri leaves to increase in CO_(2) concentration and temperature

Li-Cor 6400 Photosynthesis Measure System was used to measure the responses of photosynthetic rate,transpiration rate and stomatal conductance of Quercus fabri to increase in CO_2 concentration and temperature.The findings showed that net photosynthetic rate of Quercus fabri increased when the CO_2 concentration was increased in a very short time.When CO_2 concentration was 290-450 μmol·mol~(-1),the light compensation point(P_(LC)),light saturation point(P_(LS)),and maximun net photosynthetic rate (A_(max))were 90-100,1 500-1 700 and 5.5-8.2 μmol·m~(-2)·s~(-1),respectively.When CO_2 was increased to 700 μmol·mol~(-1),P_(LC) and P_(LS) decreased to 10 μmol·m~(-2)·s~(-1) and 1 300 μmol·m~(-2)·s~(-1),but A_(max) increased to 10.6 μmol·m~(-2)·s~(-1).The optimum temperature for the photosynthesis of Quercus fabri in spring was 24 ℃ and the corresponding P_(LS) and A_(max) were 800 μmol·m~(-2)·s~(-1) and 9.9 μmol·m~(-2)·s~(-1) respectively.The optimum temperature in summer was 28 ℃ and the corresponding P_(LS) and A_(max) were 1 700 μmol·m~(-2)·s~(-1) and 12.8 μmol·m~(-2)·s~(-1).The change of CO_2 curve at 24 ℃ was similar to that at 28 ℃.When the temperature was increased to 32 ℃,the compensatio point,saturation point and net photosynthetic rate decreased.The changes of CO_2 curve at 32 ℃,36 ℃ an 40 ℃ were similar.When the temperature was changed in a wide range,the interaction between it and CO_2 concentration was significant.Transpiration rate and stomatal conductance of leaves showed the same changing rules.They increased with the increase in the effective photosynthetic radiation and decreased with the increase in CO_2 concentration.The effect of light intensity on transpiration rate and stomatal conductance at low CO_2 concentration were greater than those at high concentration.Temperature was the main factor effecting the transpiration rate.The transpiration rate of Quercus fabri in spring was closely related to the stomata regulated by photosynthesis.In summer,however,the transpiration response to temperature greatly reflected the energy balance.Temperature and CO_2 interacted with each other.At the temperature of 24 ℃,the range of transpiration rate and stomatal conductance responded to CO_2 concentration was rather small.At 28 ℃,transpiration rate and stomatal conductance decreased with the increase in CO_2 concentration.At 32 ℃,36 ℃ and 40℃,the responses of transpiration rate and stomatal conductance took on shapes of parabolas.