Green plants fix a part of solar energy into organic matters that support all living things including plants themselves. The net primary productivity, that is the net creation of organic matters by plants, is therefore the fundamental basis determining biological diversity and activity of ecosystems on the Earth. Furthermore the fixation of carbon dioxide by vegetation is an important link in the biogeochemical cycle of carbon on the Earth. Therefore the photosynthetic activity of vegetation is expected to bring about important effects on CO2 concentration in the atmosphere.