tailieunhanh - Thermodynamics Systems in Equilibrium and Non Equilibrium Part 3

Tham khảo tài liệu 'thermodynamics systems in equilibrium and non equilibrium part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 40 Thermodynamics - Systems in Equilibrium and Non-Equilibrium The slope of the linear portion of the light-response curve Fig. 2 the quantum yield QY is a measure of the maximum realized efficiency for the conversion of light energy into carbohydrate by the leaf. When measured under similar conditions there is little variation in the maximum QY across the breadth of healthy non-stressed C3 species Ehleringer Bjorkman 1977 . This suggests there is strong selection for plants to produce leaves that are as efficient as possible in capturing solar energy in carbohydrates. Interestingly the maximum realized QY measured under ambient CO2 and O2 concentrations always falls well below the maximum potential QY determined in the lab under optimal albeit artificial controlled CO2 and O2 concentrations Skillman 2008 . This real world inefficiency is largely due to energy losses associated with photorespiration discussed below . The observed difference between the maximum potential QY and the maximum realized QY in healthy C3 plants suggests photorespiration might be a suitable target for improving photosynthetic productivity. The maximum capacity for net photosynthesis Pmax is quantified as the rate of CO2 uptake or O2 production at light-saturation Fig. 2 . Pmax measured under identical conditions varies considerably across species and varies for the same species grown under different conditions . Skillman et al. 2005 . Much of our review focuses on efforts to increase Pmax as a means of improving photosynthetic productivity. But the assumption that changes in Pmax translate to changes in whole-plant growth is open to debate Evans 1993 Kruger Volin 2006 Poorter Remkes 1990 . The solid diagonal line in Fig. 2 takes its slope from the linear portion of the light response curve QY . This shows that in principle if there were no upper saturation limit on Pmax increasing absorbed light would continue to produce increasing amounts of carbohydrate all the way up to full-sun 2000