Photosynthesis is the process where green plants use sunlight, carbon dioxide, and water to make food and oxygen according to the formula,
6CO2 + 6H2O + energy -> C6H12O6 + 6O2
Respiration is the process where cells use oxygen and this food (in the absence of light) to release carbon dioxide, water and the stored energy,
6O2 + C6H12O6 -> 6CO2 + 6H2O + energy
The SAME amount of carbon dioxide is required and released during photosynthesis and respiration, respectively.
NPP or Net Primary Production, is an indicator of how much net carbon is stored or fixed by plants. Gross Primary Production (GPP) is the rate at which the plants capture and store a given amount of chemical energy as biomass in a given length of time. Some fraction of this fixed energy is used for cellular respiration and maintenance of existing tissues. In brief,
NPP = GPP – Respiration by plants
NPP was estimated to be in the ranged from 120 to 1660 grams carbon per square meter per year (Waring et al., 1998)
It is the NPP that humans depend on for food, fiber, building, packaging materials, biofuels, et cetera. Humans are using an increasing amount of Earth’s annual NPP and the consumption reportedly rose from 20 to 25 percent from 1995 to 2005.
Humans always have the tendency to plant more trees in hoping that more carbon dioxide can be sequestered and issues of deforestation resolved. But, does it really help?
Reference
R. H. Waring, J. J. Landsberg and M. Williams. 1998. Net primary production of forests: a constant fraction of gross primary production? Tree Physiology 18, 129-134