Photosynthesis system

Photosynthesis systems are electronic scientific instruments designed for non-destructive measurement of photosynthetic rates in the field. Photosynthesis systems are commonly used in agronomic and environmental research, as well as studies of the global carbon cycle.
How photosynthesis systems function.
Photosynthesis systems function by measuring gas exchange of leaves. Atmospheric carbon dioxide is taken up by leaves in the process of photosynthesis, where is used to generate sugars in a molecular pathway known as the Calvin cycle. This draw-down of induces more atmospheric to diffuse through stomata into the air spaces of the leaf. While stoma are open, water vapor can easily diffuse out of plant tissues, a process known as transpiration. It is this exchange of and water vapor that is measured as a proxy of photosynthetic rate.
The basic components of a photosynthetic system are the leaf chamber, infrared gas analyzer (IRGA), batteries and a console with keyboard, display and memory. Modern 'open system' photosynthesis systems also incorporate miniature disposable compressed gas cylinder and gas supply pipes. This is because external air has natural fluctuations in and water vapor content, which can introduce measurement noise. Modern 'open system' photosynthesis systems remove the and water vapour by passage over soda lime and Drierite, then add at a controlled rate to give a stable concentration. Some systems are also equipped with temperature control and a removable light unit, so the effect of these environmental variables can also be measured.
The leaf to be analysed is placed in the leaf chamber. The concentrations is measured by the infrared gas analyzer. The IRGA shines infrared light through a gas sample onto a detector. in the sample absorbs energy, so the reduction in the level of energy that reaches the detector indicates the concentration. Modern IRGAs take account of the fact that absorbs energy at similar wavelengths as . Modern IRGAs may either dry the gas sample to a constant water content or incorporate both a and a water vapour IRGA to assess the difference in and water vapour concentrations in air between the chamber entrance and outlet.
The Liquid Crystal Display on the console displays measured and calculated data. The console may have a PC card slot. The stored data can be viewed on the LCD display, or sent to a PC. Some photosynthesis systems allow communication over the internet using standard internet communication protocols.
Modern photosynthetic systems may also be designed to measure leaf temperature, chamber air temperature, PAR (photosynthetically active radiation), and atmospheric pressure. These systems may calculate water use efficiency (A/E), stomatal conductance (gs), intrinsic water use efficiency (A/gs), and sub-stomatal concentration (Ci). Chamber and leaf temperatures are measured with a thermistor sensor. Some systems are also designed to control environmental conditions.
A simple and general equation for Photosynthesis is:
+ + (Light Energy)→ C6H12O6+O2
'Open' systems or 'closed' systems.
There are two distinct types of photosynthetic system; ‘open’ or ‘closed’. This distinction refers to whether or not the atmosphere of the leaf-enclosing chamber is renewed during the measurement.
In an ‘open system’, air is continuously passed through the leaf chamber to maintain in the leaf chamber at a steady concentration. The leaf to be analysed is placed in the leaf chamber. The main console supplies the chamber with air at a known rate with a known concentration of and . The air is directed over the leaf, then the and concentration of air leaving the chamber is determined. The out going air will have a lower concentration and a higher concentration than the air entering the chamber. The rate of uptake is used to assess the rate of photosynthetic carbon assimilation, while the rate of water loss is used to assess the rate of transpiration. Since intake and release both occur through the stomata, high rates of uptake are expected to coincide with high rates of transpiration. High rates of uptake and loss indicates high stomatal conductance.
Because the atmosphere is renewed, 'open' systems are not seriously affected by outward gas leakage and adsorption or absorption by the materials of the system.
In contrast, in a ‘closed system’, the same atmosphere is continuously measured over a period of time to establish rates of change in the parameters. The concentration in the chamber is decreased, while the concentration increases. This is less tolerant to leakage and material ad/absorption.
Calculating photosynthetic rate and related parameters.
Calculations used in 'open system' systems;.
For CO2 to diffuse into the leaf, stomata must be open, which permits the outward diffusion of water vapour. Therefore, the conductance of stomata influences both photosynthetic rate (A) and transpiration (E), and the usefulness of measuring A is enhanced by the simultaneous measurement of E. The internal concentration (Ci) is also quantified, since Ci represents an indicator of the availability of the primary substrate (CO2) for A.
A carbon assimilation is determined by measuring the rate at which the leaf assimilates . The change in is calculated as flowing into leaf chamber, in μmol mol−1 , minus flowing out from leaf chamber, in μmol mol−1. The photosynthetic rate (Rate of exchange in the leaf chamber) is the difference in concentration through chamber, adjusted for the molar flow of air per m2 of leaf area, mol m−2 s−1.
The change in H2O vapour pressure is water vapour pressure out of leaf chamber, in mbar, minus the water vapour pressure into leaf chamber, in mbar. Transpiration rate is differential water vapour concentration, mbar, multiplied by the flow of air into leaf chamber per square meter of leaf area, mol s−1 m−2, divided by atmospheric pressure, in mBar.
Calculations used in 'closed system' systems;.
A leaf is placed in the leaf-chamber, with a known area of leaf enclosed. Once the chamber is closed, carbon dioxide concentration gradually declines. When the concentration decreases past a certain point a timer is started, and is stopped as the concentration passes at a second point. The difference between these concentrations gives the change in carbon dioxide in ppm. Net photosynthetic rate in micro grams carbon dioxide s−1 is given by;
(V • p • 0.5 • FSD • 99.7) / t
where V = the chamber volume in liters, p = the density of carbon dioxide in mg cm−3, FSD = the carbon dioxide concentration in ppm corresponding to the change in carbon dioxide in the chamber, t = the time in seconds for the concentration to decrease by the set amount. Net photosynthesis per unit leaf area is derived by dividing net photosynthetic rate by the leaf area enclosed by the chamber.
Applications.
Since photosynthesis, transpiration and stomatal conductance are an integral part of basic plant physiology, estimates of these parameters can be used to investigate numerous aspects of plant biology. The plant-scientific community has generally accepted photosynthetic systems as reliable and accurate tools to assist research. There are numerous peer-reviewed articles in scientific journals which have used a photosynthetic system. To illustrate the utility and diversity of applications of photosynthetic systems, below you will find brief descriptions of research using photosynthetic systems;