Biomedical subjects

Siegfried Jahnke

Publications and source records attributed to Siegfried Jahnke.

3 recordsLinked to original sources

PubMed2006

Air pressure in clamp-on leaf chambers: a neglected issue in gas exchange measurements.

Air pressure in leaf chambers is thought to affect gas exchange measurements through changes in partial pressure of the air components. However, other effects may come into play when homobaric leaves are measured in which internal lateral gas flow may occur. When there was no pressure difference between the leaf chamber and ambient air (DeltaP=0), it was found in previous work that lateral CO(2) diffusion could affect measurements performed with clamp-on leaf chambers. On the other hand, overpressure (DeltaP>0) in leaf chambers has been reported to minimize artefacts possibly caused by leaks in chamber sealing. In the present work, net CO(2) exchange rates (NCER) were measured under different DeltaP values (0.0-3.0 kPa) on heterobaric and homobaric leaves. In heterobaric leaves which have internal barriers for lateral gas movement, changes in DeltaP had no significant effect on NCER. For homobaric leaves, effects of DeltaP>0 on measured NCER were significant, obviously due to lateral gas flux inside the leaf mesophyll. The magnitude of the effect was largely defined by stomatal conductance; when stomata were widely open, the impact of DeltaP on measured NCER was up to 7 mumol CO(2) m(-2) s(-1) kPa(-1). Since many other factors are also involved, neither DeltaP=0 nor DeltaP>0 was found to be the 'one-size fits all' solution to avoid erroneous effects of lateral gas transport on measurements with clamp-on leaf chambers.

Air Pressure↗

PubMed2006

Lateral diffusion of CO2 from shaded to illuminated leaf parts affects photosynthesis inside homobaric leaves.

Gas exchange is generally regarded to occur between the leaf interior and ambient air, i.e. in vertical (anticlinal) directions of leaf blades. However, inside homobaric leaves, gas movement occurs also in lateral directions. The aim of the present study was to ascertain whether lateral CO2 diffusion affects leaf photosynthesis when illuminated leaves are partially shaded. Measurements using gas exchange and chlorophyll fluorescence imaging techniques were performed on homobaric leaves of Vicia faba and Nicotiana tabacum or on heterobaric leaves of Glycine max and Phaseolus vulgaris. For homobaric leaves, gas exchange inside a clamp-on leaf chamber was affected by shading the leaf outside the chamber. The quantum yield of photosystem II (Phi(PSII)) was highest directly adjacent to a light/shade border (LSB). Phi(PSII) decreased in the illuminated leaf parts with distance from the LSB, while the opposite was observed for nonphotochemical quenching. These effects became most pronounced at low stomatal conductance. They were not observed in heterobaric leaves. The results suggest that plants with homobaric leaves can benefit from lateral CO2 flux, in particular when stomata are closed (e.g. under drought stress). This may enhance photosynthetic, instead of nonphotochemical, processes near LSBs in such leaves and reduce the photoinhibitory effects of excess light.

Carbon Dioxide↗

PubMed2005

Lateral gas diffusion inside leaves.

Diffusion of CO2 inside leaves is generally regarded to be from the substomatal cavities to the assimilating tissues, i.e. in the vertical direction of the leaf blades. However, lateral gas diffusion within intercellular air spaces may be much more effective than hitherto considered. In a previous work it was demonstrated that, when 'clamp-on' leaf chambers are used, leaf internal 'CO2 leakage' beyond the leaf chamber gaskets may seriously affect gas exchange measurement. This effect has been used in the present paper to quantify gas conductance (g(leaf,l), mmol m(-2) s(-1)) in the lateral directions within leaves and significant differences between homo- and heterobaric leaves were observed. For the homobaric leaves, lateral gas conductance measured over a distance of 6 or 8 mm (the widths of the chamber gaskets) was 2-20% of vertical conductance taken from published data measured over much smaller distances of 108-280 microm (the thickness of the leaves). The specific internal gas diffusion properties of the leaves have been characterized by gas conductivities (g*(leaf), micromol m(-1) s(-1)). Gas conductivities in the lateral directions of heterobaric leaves were found to be small but not zero. In homobaric leaves, they were between 67 and 209 micromol m(-1) s(-1) and thus even larger than those in the vertical direction of the leaf blades (between 15 and 78 micromol m(-1) s(-1)). The potential implications for experimentalists performing gas exchange measurements are discussed.

Carbon Dioxide↗