13.6 Gas Exchange and Photosynthesis Sensors
The photosynthesis process is considered the most important biochemical reaction
because it allows plants to transform sunlight energy into chemical energy (MillanAlmaraz et al. 2013). Because of this, plants fix carbon dioxide (CO 2 ) and release
oxygen (O 2 ). This process is considered the most important biochemical reaction in
the world because it produces 90 % of the planet biomass (Taiz and Zeiger 2006).
On the other hand, photo-inhibition is a term utilized to describe all the environmental conditions that can negatively affect the photosynthetic activity. The most
common stress factor is light. Consequently, accurate photosynthesis measurements are necessary to establish comparisons and understand plant productivity or
biomass accumulation at the leaf, plant, canopy, or community levels as well as
their interaction and response to environmental (Bakker et al. 2001), chemical
(Marschner 1995), or biological (Stout et al. 1999) factors that generate stress
conditions. Here, it can be inferred that it is very important the photosynthesis
measurement because it reflect the whole crop biomass production which where it is
very important to maintain high yields at the new generation plant factories.
There are many methods to perform photosynthesis measurements. However,
the gas exchange method is currently the most commonly utilized technique to
achieve this by measuring carbon dioxide exchange. Because of this, this method
is widely utilized in commercial equipment and experimental setups in order to
measure individual leaves, whole plants, plant canopy, and even forests (MillanAlmaraz et al. 2009; Schulze 1972; Bassow and Bazzaz 1998). This methodology
is based on isolating the specimen or sample under analysis in a closed chamber to
measure the initial gas concentration when the chamber is closed. After a few
minutes, the chamber has been closed, recording changes in the proportions of
gases from the air inside the chamber produced by the plant is also carried out.
Consequently, it is possible to measure the gas exchange by analyzing O 2 or CO 2
concentration (Schulze 1972; Takahashi et al. 2001). There are two types of gas
exchange designs: closed chambers where the sample is completely enclosed to
measure the difference in gas without contact with outside air and the open
chambers where air can freely enter and leave the chamber flowing through the
sample (Hunt 2003).
Infrared sensors for gas analysis (IRGA) are the most utilized for CO 2 measurement and are based on an infrared emitter-photo detector par whose light beam
is used to measure the concentration of gas molecules in the air. This is based on
the absorption phenomenon of the light beam by molecules in a gaseous state
(Hunt 2003). This phenomenon of absorption occurs because the heteroatomic gas
molecules with odd number of atoms such as CO 2 , CH 4 , NH 3 , to name a few,
absorb a portion of the infrared light while the homoatomic gas molecules such as
N 2 and O 2 do not. The CO 2 has a maximum detection at a wavelength of 4.25 lm,
with peaks side of 2.66, 2.77 and 14.99 lm (Hill and Powell 1968). The calibration
of these sensors to zero adjustment requires air free of CO 2 and other heteroatomic
gases; therefore N 2 is most often used for calibration purposes. Also, the
376
M. S. Acosta-Navarrete et al.
The photosynthesis process is considered the most important biochemical reaction
because it allows plants to transform sunlight energy into chemical energy (MillanAlmaraz et al. 2013). Because of this, plants fix carbon dioxide (CO 2 ) and release
oxygen (O 2 ). This process is considered the most important biochemical reaction in
the world because it produces 90 % of the planet biomass (Taiz and Zeiger 2006).
On the other hand, photo-inhibition is a term utilized to describe all the environmental conditions that can negatively affect the photosynthetic activity. The most
common stress factor is light. Consequently, accurate photosynthesis measurements are necessary to establish comparisons and understand plant productivity or
biomass accumulation at the leaf, plant, canopy, or community levels as well as
their interaction and response to environmental (Bakker et al. 2001), chemical
(Marschner 1995), or biological (Stout et al. 1999) factors that generate stress
conditions. Here, it can be inferred that it is very important the photosynthesis
measurement because it reflect the whole crop biomass production which where it is
very important to maintain high yields at the new generation plant factories.
There are many methods to perform photosynthesis measurements. However,
the gas exchange method is currently the most commonly utilized technique to
achieve this by measuring carbon dioxide exchange. Because of this, this method
is widely utilized in commercial equipment and experimental setups in order to
measure individual leaves, whole plants, plant canopy, and even forests (MillanAlmaraz et al. 2009; Schulze 1972; Bassow and Bazzaz 1998). This methodology
is based on isolating the specimen or sample under analysis in a closed chamber to
measure the initial gas concentration when the chamber is closed. After a few
minutes, the chamber has been closed, recording changes in the proportions of
gases from the air inside the chamber produced by the plant is also carried out.
Consequently, it is possible to measure the gas exchange by analyzing O 2 or CO 2
concentration (Schulze 1972; Takahashi et al. 2001). There are two types of gas
exchange designs: closed chambers where the sample is completely enclosed to
measure the difference in gas without contact with outside air and the open
chambers where air can freely enter and leave the chamber flowing through the
sample (Hunt 2003).
Infrared sensors for gas analysis (IRGA) are the most utilized for CO 2 measurement and are based on an infrared emitter-photo detector par whose light beam
is used to measure the concentration of gas molecules in the air. This is based on
the absorption phenomenon of the light beam by molecules in a gaseous state
(Hunt 2003). This phenomenon of absorption occurs because the heteroatomic gas
molecules with odd number of atoms such as CO 2 , CH 4 , NH 3 , to name a few,
absorb a portion of the infrared light while the homoatomic gas molecules such as
N 2 and O 2 do not. The CO 2 has a maximum detection at a wavelength of 4.25 lm,
with peaks side of 2.66, 2.77 and 14.99 lm (Hill and Powell 1968). The calibration
of these sensors to zero adjustment requires air free of CO 2 and other heteroatomic
gases; therefore N 2 is most often used for calibration purposes. Also, the
376
M. S. Acosta-Navarrete et al.