Carbon dioxide fixation and water use efficiency are only now beginning to be understood in detail. When considering C02 fixation, plants are grouped into three main biological classifications - C3, C4 and CAM, abbreviated names for plants that share a predominance of the same chemical bonding sites (receptor sites) for carbon dioxide. Once the bonding process is complete, a series of chemical reactions occur to break down the C02 and water to create carbohydrates.
Photo: scrippsnews.ucsd.edu
To help understand the process more simply, plants absorb C02 using C3, C4 and CAM receptors, much like the body absorbs oxygen with haemoglobin, which has a high affinity for oxygen.
The difficulty facing researchers is that not all plants share the same receptor sites. It is known that C3 plants, of which some 95% or more of the biomass is comprised, utilise ambient C02 directly into their photosynthetic carbon reduction cycle. In terms of water utilisation, this is the least efficient category and includes plants such as cotton, rice, wheat and sugar-beets.
C4 plants, such as maize, sorghum, millet and sugarcane, have a higher water-use efficiency because an enzyme-based, C02-concentrating mechanism begins the photosynthetic process and allows higher stomatal resistance and less transpiration for the same C02 fixation.
by: Steven Carruthers
Carbon dioxide fixation
9:35 PM
ThanateTan
