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. 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. Photosynthesis systems function by measuring gas exchange of leaves. Atmospheric carbon dioxide is taken up by leaves in the process of photosynthesis, where CO2 is used to generate sugars in a molecular pathway known as the Calvin cycle. This draw-down of CO2 induces more atmospheric CO2 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 CO2 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 CO2 and water vapor content, which can introduce measurement noise. Modern 'open system' photosynthesis systems remove the CO2 and water vapour by passage over soda lime and Drierite, then add CO2 at a controlled rate to give a stable CO2 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 CO2 concentrations is measured by the infrared gas analyzer. The IRGA shines infrared light through a gas sample onto a detector. CO2 in the sample absorbs energy, so the reduction in the level of energy that reaches the detector indicates the CO2 concentration. Modern IRGAs take account of the fact that H2O absorbs energy at similar wavelengths as CO2. Modern IRGAs may either dry the gas sample to a constant water content or incorporate both a CO2 and a water vapour IRGA to assess the difference in CO2 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 CO2 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:CO2+ H2O+ (Light Energy)→ C6H12O6+O2 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 CO2 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 CO2 and H2O. The air is directed over the leaf, then the CO2 and H2O concentration of air leaving the chamber is determined. The out going air will have a lower CO2 concentration and a higher H2O concentration than the air entering the chamber. The rate of CO2 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 CO2 intake and H2O release both occur through the stomata, high rates of CO2 uptake are expected to coincide with high rates of transpiration. High rates of CO2 uptake and H2O loss indicates high stomatal conductance.