Effects Of Summer And Autumn Seasons Warming And Elevate CO₂Concentration On Dark Respiration And Photosynthetic Characteristics Of Rosa Chinensis In Beijing Urban Area

Leaf dark respiration(R) plays an important role in plant carbon balance, the light inhibition of dark respiration seems to depend on the photosynthetic processes, and to lead to daytime carbon loss of plant leaves, which has important ecological effects on plant carbon balance. In this research, we used Li6400to make warming and elevate CO2concentration treatments to leaves of Rosa chinensis at28℃in Summer and20℃in Autumn in Beijing urban areas, the warming intervals are:2℃(28℃-30℃) and5℃(28℃-30℃) in Summer,3℃(20℃-23℃) and5℃(20℃-25℃) in Autumn; The CO2concentration controled to380、430、550umolmol-1. We simulated Summer and Autumn warming and elevating CO2concentration to affect dark respiration and photosynthetic characteristics of Rosa chinensis in the urban areas of Beijing. The results showed that:(1) Transpiration rate (Tr) increased dramatically with the increase of temperature, and stomatal conductance (Gs) increased at first, but decreased later with increasing temperature. Autumn warming and Summer warming had significant effects (p<0.05) on transpiration rate (Tr), but intercellular CO2concentration (Ci) was not significant (p>0.05).(2) In daytime warming of5℃in Summer for RL was significantly higher than that in daytime warming of2℃(p<0.05),but daytime warming of2℃had not obvious significances (p>0.05); In daytime warming in Autumn of5℃for RL was also significantly higher than that in daytime warming of3℃(p<0.05), but daytime warming of3℃had not obvious significances (p>0.05). Four warming treatments in Summer and Autumn had significant effects (p<0.05) on daytime R measured by shading leaves (RD).(3)Warming of5℃(20℃-25℃) in Autumn had significant effects (p<0.05) on light-inhibited leaf R, but the other three warming treatments were not significant (p>0.05). The maximum value of light-inhibited leaf R((47.3±6.731)%) appeared in20℃in Autumn, the minimum value ((19.9±6.897)%) appeared in33℃in Summer.(4) In Autumn, the sensitivity of leaf dark respirations of RL and RD to temperature variations is higher during warming of5℃than warming of3℃(p<0.05). In Summer, warming of2℃and5℃for leaf dark respirations of RL and RD had not significant differences (p>0.05).for the warming of5℃in Autumn, the sensitivity of light-inhibited leaf R to temperature is significantly higher than the other three warming treatments.(5) Transpiration rate (Tr) and stomatal conductance (Gs) increased at first, but decreased later with the increase of CO2concentration, but the intercellular CO2concentration (Ci) increased at28℃in Summer and20℃in Autumn. The elevating CO2concentration had significant effects on intercellular CO2concentration (Ci).(6) Daytime respiration in light (RL) and daytime respiration measured by shading leaves (RD) decreased with the increase of CO2concentration at28℃in Summer and20℃in Autumn. RD at air temperature28℃was significantly higher than that at20℃in all elevating CO2concentration. Temperature and CO2concentration were influence on leaf dark respirations main ecological factors.(7) Light-inhibited leaf respiration increased with the increase of CO2concentration at20℃in Autumn, the maximum value ((47.3±6.731)%) appeared in550umolmol-1of CO2concentration; In Summer28℃light-inhibited leaf respiration increased at first, but decreased later with the increase of CO2concentration. In Autumn20℃elevating CO2concentration had more effects on light-inhibited leaf respiration. The findings in our study are important for improving the estimation method of urban plant carbon loss under daytime warming and elevating CO2concentration in urban areas, and is also beneficial to help build analyzing method of plant carbon sinks for urban green spaces.