AP4 Leaf Porometer from Delta-T (5 YEAR WARRANTY)


Delta T


Stomatal aperture is the dominant factor in the diffusion conductance of leaf surfaces, which controls both the water loss from plant leaves and the uptake of CO2 for photosynthesis. Measurements of diffusion conductance are therefore important indicators of plant water status and provide valuable insight into plant growth and plant adaptation to environmental variables.

8 550,00 €

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Type of Instrument Leaf Porometer
The instrument measures: Stomatal Conductance

AP4 Leaf Porometer 

  • Direct readout of stomatal conductance or stomatal resistance of leafs
  • Simple absolute calibration in the field
  • Minimises leaf stress during measurement
  • Ideal for Phenotyping based research  
  • Award-winning user interface

The AP4 Leaf Porometer measures diffusion conductance by comparing the precise rate of humidification within a small cuvette to readings obtained with a calibration plate. The plate has 6 diffusion conductance settings whose values have been accurately determined by finite element analysis.

Quoted accuracy figures for other porometers and gas analysis systems are based on time-consuming laboratory set-up and calibrations which bear little comparison to field conditions. In contrast, the AP4 Leaf Porometer features simple direct calibration in the field against a tested physical standard.

The AP4 Leaf Porometer
 has many other features designed to ensure that accurate, reproducible readings can be taken as easily as possible:


  • Sophisticated temperature compensation
  • Unstirred leaf chamber minimises unwanted stomatal closure
  • Lightweight ergonomic sensor head
  • Large clear LCD display (8 lines by 40 characters)
  • Full QWERTY keypad for annotating up to 1500 readings
  • Over 2,000 Delta-T porometers in use worldwide

Dynamic diffusion porometers, such as the AP4, are also known as stomatal diffusion porometers.



Reading range



Test Conditions





Reading range


5.0 -1200 mmol m-2 s-1

0.1 - 10

± 10 %

5 - 800 mmol m-2 s-1

± 20 %

800 - 1200 mmol m-2 s-1


0.25 - 30.0 mm s-1

0.01 - 0.1

± 10%

0.25 - 20 mm s-1

± 20 %

20 - 30 mm s-1


0.2 - 40 s cm-1

0.01 - 0.1

± 10 %

0.5 - 40 s cm-1

± 0.2 s cm-1

0.2 - 0.5 s cm-1


0 - 100%


± 4%


Cup temp

-5 - +55 °C


± 0.7 °C

0 - 50 °C

Cup-leaf temp

-5 - +5 °C


± 0.2 °C

0 - 50 °C

PAR flux[3]

0 - 2500 µmol m-2 s-1


± 15%



600 - 1200 hPa, settable in steps of 5 hPa


RH cycle level

20 - 80 %RH, settable in steps of 5%



  • Resolution varies with the magnitude of the value obtained. The range shown corresponds to the reading range. In relative terms, the resolution is better than 2%, but at least the smallest amount shown.
  • The stated accuracy applies over the range of the calibration plate and for optimum cup conditions, i.e. from +10 to -5 °C difference between actual cup temp. and that existing at calibration, and for +2.5 to -2.5 °C difference between leaf and cup temperatures.
  • Spectral and cosine responses are approximate only.
  • Ambient pressure may be read from a Wristwatch Barometer type PBR1.
  • Cycling at extreme combinations of temperature, conductance and RH level may not always be possible.

Optional Accessories
PBR1  Wristwatch barometer for AP4
PCK1  Spare AP4 consumables kit
PSK2  AP4 Spares Kit (incl manual)
PSH1  Spare AP4 sensor head
PSB2  Spare AP4 rechargeable battery v2
PAD  Paper pads for AP4 calibration
AP-CHG  Spare AP4 battery charger
AP-CP  Spare AP4 calibration plate
AP4-UM  AP4 User Manual
USB-RS232  USB to RS232 adapter cable


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