234
L. Kappen et al.
system now includes an AT 286 computer. The image analysis is performed
on a RGB computer monitor connected to a digitizing board (Bartscher
Elektronik, Eschwege, Germany). For the documentation of images a
streamer is used. Further details about hard- and software will be published
elsewhere. The CO2 exchange cuvette is installed in a walk-in environmental
chamber, and the electronic control and computer devices are in an adjacent
dry room.
Changes in stomatal aperture are recorded over time periods of 40 s.
Each image is stored for later analysis. The contrast of the images is
intensified by gray color shifting. Although it is well established that stomatal width better describes the stomatal conductance (Meidner and Mansfield 1968), we are at present using area evaluation for comparative terms.
Changes in stomatal aperture are due not only to changes in the width alone
(e.g., in Vicia faba), they also result from an overall change in elliptic
parameters, including the long axis, as in Tradescantia albiflora (Kappen and
Haeger 1991). Thus, the parameters taken as proportional for stomatal
response depend on the species observed.
11.3 General Aspects
The data presented in this study illustrate not only the capacity and potentials but also the limitations of a newly developed method. The advantage
lies in directly measuring stomatal movements in response to any trigger.
These measurements are successful only if the real pore width can be
depicted. Stomatal width or aperture can be used as a proportional measure
if related to the same stoma in a time series or, with restrictions, to a
repeatedly observed identical population of 20 to 50 stomata in the same
experiment. Otherwise, relative degrees of opening may be used in order to
compare different plant specimens or species.
Plant species can be investigated by our method only if their stomata are
large enough (the central aperture must be easily visible in the optical
system). A screening test run with leaves of 150 plant species (Schultz 1990)
revealed that 43 taxa fulfilled these conditions. Of 61 woody plant species,
13 were suited for further investigations (e.g., Euonymus europaea, Betula
pubescens, Juglans regia, Populus nigra, Sambucus nigra, Vitis vinifera) and
of 25 hemicryptophytic herbaceous plant species, 12 were suitable (e.g.,
Aegopodium podagraria, Atropa belladonna, Ranunculus repens). Only a
few grass species proved useful (Avena sativa, but not Zea mays).
Figure 11.3 illustrates the response time needed for stomatal aperture to
reach steady state after an experimental increase of the water vapor pressure
deficit (VPD) air to leaf from 5 mbar bar- 1 to 11 mbar bar- 1 (irradiance
was 550 ~mol photons m - 2 S -1 PAR). An initial oscillation of the stomatal
aperture is eliminated in this graph. The response time varied between 25
L. Kappen et al.
system now includes an AT 286 computer. The image analysis is performed
on a RGB computer monitor connected to a digitizing board (Bartscher
Elektronik, Eschwege, Germany). For the documentation of images a
streamer is used. Further details about hard- and software will be published
elsewhere. The CO2 exchange cuvette is installed in a walk-in environmental
chamber, and the electronic control and computer devices are in an adjacent
dry room.
Changes in stomatal aperture are recorded over time periods of 40 s.
Each image is stored for later analysis. The contrast of the images is
intensified by gray color shifting. Although it is well established that stomatal width better describes the stomatal conductance (Meidner and Mansfield 1968), we are at present using area evaluation for comparative terms.
Changes in stomatal aperture are due not only to changes in the width alone
(e.g., in Vicia faba), they also result from an overall change in elliptic
parameters, including the long axis, as in Tradescantia albiflora (Kappen and
Haeger 1991). Thus, the parameters taken as proportional for stomatal
response depend on the species observed.
11.3 General Aspects
The data presented in this study illustrate not only the capacity and potentials but also the limitations of a newly developed method. The advantage
lies in directly measuring stomatal movements in response to any trigger.
These measurements are successful only if the real pore width can be
depicted. Stomatal width or aperture can be used as a proportional measure
if related to the same stoma in a time series or, with restrictions, to a
repeatedly observed identical population of 20 to 50 stomata in the same
experiment. Otherwise, relative degrees of opening may be used in order to
compare different plant specimens or species.
Plant species can be investigated by our method only if their stomata are
large enough (the central aperture must be easily visible in the optical
system). A screening test run with leaves of 150 plant species (Schultz 1990)
revealed that 43 taxa fulfilled these conditions. Of 61 woody plant species,
13 were suited for further investigations (e.g., Euonymus europaea, Betula
pubescens, Juglans regia, Populus nigra, Sambucus nigra, Vitis vinifera) and
of 25 hemicryptophytic herbaceous plant species, 12 were suitable (e.g.,
Aegopodium podagraria, Atropa belladonna, Ranunculus repens). Only a
few grass species proved useful (Avena sativa, but not Zea mays).
Figure 11.3 illustrates the response time needed for stomatal aperture to
reach steady state after an experimental increase of the water vapor pressure
deficit (VPD) air to leaf from 5 mbar bar- 1 to 11 mbar bar- 1 (irradiance
was 550 ~mol photons m - 2 S -1 PAR). An initial oscillation of the stomatal
aperture is eliminated in this graph. The response time varied between 25