BF Agritech - ITSystems

PTM-48A Photosynthesis Monitor

Overview

The PTM-48A Monitor is truly state-of-the-art system for long-term automatic recording physiological characteristics of intact plants. The Monitor has four inputs for original automatic self-clamping leaf chambers. The chamber is normally open and shuts the leaf only for 30 seconds to take readings of both CO2 and H2O exchange rates. The short measurement time provides minimal disturbance of natural leaf conditions. The standard LC-4B Leaf Chamber has a 20 cm2 aperture suitable for a wide variety of broad-leaf plants. Any LC-4B leaf chamber may be equipped with the optional leaf temperature sensor that enables additional recording of stomatal conductance for that particular leaf chamber. A new optional LC-4D Opaque Leaf Chamber allows partitioning of the leaf CO2 exchange that is based on PIB (post-illuminance burst) technique. Paired LC-4B and LC-4D leaf chambers provides evaluation of photorespiration, dark respiration, gross and net photosynthesis. The monitor has also 8 analog inputs for optional sensors and one digital input for RTH-48. The Monitor provides fully automatic continuous operation with sampling rate selectable from 5 to 120 minutes. The Monitor is a portable 12 VDC instrument. The RS-232 and RS-485 ports may be used for communicating with the PC. Either 2.4 GHz Radio or GPRS modem may be used for remote operation. The Terminal Emulator software allows controlling system setup and operation as well as data downloading and export in TXT or CSV format for further processing and analysis. A simple graphics viewer is also available.

Basic Configuration

in presence of the LT-LC leaf temperature sensor

Specifications

Number of leaf chambers	4
Leaf chamber area window	20 cm2
Standard length of connecting hose	4 m
Normal range of airflow rate in the leaf chamber channel	0.8 to 1.0 lpm
CO2 concentration measurement range	0 to 1000 ppm
Rated measurement range of CO2 exchange	−70 to 70 µmolCO2·m−2·s−1
Transpiration measurement range	0 to 150 mgH2O·m−2·s−1
Built-in RTH-48 Meter for measuring Photosynthetic Radiation, Air Temperature, Relative Humidity and Leaf Wetness. Has input for the digital SMTE Soil Moisture, Temperature and EC sensor.
Number of analog inputs for optional sensors	8
Input range for optional sensors	Programmable, 0—1 to 0—20 VDC
Power requirements	12 VDC @ 60 W max.
Interface	RS232 and RS485. Optional RF or GPRS modems.
Terminal Emulator and Graphics software for Windows.
Environmental protection index	IP 55

Partitioning of the CO2 Exchange

Illuminated leaves exhibit large transient CO2 release when first exposed to darkness. This rapid increase is termed the respiratory post-illumination burst (PIB), followed by a second slower rise in respiration, which is termed light-enhanced-dark-respiration (LEDR). The first peak of post-illumination CO2 release is usually considered as indication of photorespiration rate. The PIB technique may be easily realized in PTM-48A Monitor by using a leaf chamber with opaque window. Thus, by using a pair of leaf chambers, the regular transparent chamber and the opaque one, the Monitor may represent a full cycle of CO2 exchange that allows a keen user to realize partitioning of the leaf CO2 exchange.

The LC-4B Leaf chamber starts the measuring cycle, then, the opaque LC-4D camber put the leaf to darkness. The typical record of the CO2 Analyzer on C3 plants is shown in the picture:


Measurement cycle phases Stand-by (both open) LC-4B — Net photosynthesis LC-4D — Dark exposition

LC-4D Leaf Chamber

The LC-4D Leaf Chamber and the above mentioned technique was tested extensively in the Laboratory of Bioenergetics of the Institute of Plant Ecology and Physiology of the Moldova Academy of Sciences. The results may be presented by request.

Stomatal Conductance

LT-LC Leaf Temperature sensor probe on leaf

The flux of water vapor from the leaves can be expressed by the following equation proposed by Gaastra:

Tr = (Hleaf − Hatm)/(rs + rb) ,(1) where

Tr: — flux of water vapor
Hleaf: — concentration of water vapor at the surface of mesophyll cells
Hatm: — concentration of water vapor in the bulk of atmosphere
rs: — epidermis resistance to water vapor diffusion
rb: — boundary layer resistance to water vapor diffusion

Hence,

rs = (Hleaf − Hatm)/Tr − rb ,(2)

and

σs = 1/rs ,

where

σs: — stomatal conductance

If to apply the Equation to the LC-4B leaf chamber, one may conclude that Tr and Hatm are measured by the PTM-48A Monitor, rb is a characteristic of the LC-4B leaf chamber and air flow rate in it, which has been found equal to 220 s/m. The value of Hleaf is actually a concentration of the saturated vapor at the leaf temperature, which can be measured by optional LT-LC sensor.

The LT-LC Leaf Temperature Sensor has a stainless steel wire clip for fixing on a leaf chamber. The miniature bead thermistor has good contact with the leaf due to oblong elastic plate. The thermistor's leads are positioned along a leaf surface to minimize effect on leaf temperature. The LT-LC sensor may be connected to any of eight optional analog inputs of the PTM-48A Photosynthesis Monitor. Evaluation of the leaf stomatal conductance is based on the measured transpiration rate and the known conductance of the boundary layer inside the LC-4B leaf chamber.

When configuring the sensor in the PC program, the user shall specify input number of the leaf chamber equipped with the LT-LC sensor. Two new column will appear in the data table of the leaf chamber: initial leaf temperature and stomatal conductance.
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