Photosynthesis, Respiration, and Net Primary Production of Sunflower Stands in Ambient and Elevated Atmospheric CO2 Concentrations: An Invariant NPP:GPP Ratio? Glob. Chang. Biol. 2000, 6, 931–941. [Google Scholar] [CrossRef] [Green Version] Tramontana, G.; Migliavacca, M.; Jung, M.; ...