title: Do secondary substances in the thallus of a lichen promote CO2diffusion and prevent depression of net photosynthesis at high water content?
abstract: Many lichens show seriously depressed net photosynthesis (NP) at high thallus water contents due to increased carbon dioxide diffusion resistance through blockage of diffusion pathways by water. The soil lichen Diploschistes muscorum, however, shows no depression and NP is close to maximal even at the highest thallus water content. We investigated whether lichen substances (lecanoric and diploschistesic acids) in the cortex and medulla contributed to this ability to maintain high NP. Dry thalli were extracted with water-free acetone and, after this treatment, were found to be fully viable to the extent of continued growth after replanting in the field. No differences were found in the response of NP to thallus water content between the normal and extracted thalli, in fact the response curves were often nearly identical. Thus, in this species it seems that lichen substances did not maintain the water-free diffusion pathways and some other explanation, possibly structural, needs to be sought.
authors.affiliation: Julius-von-Sachs-Institut für Biowissenschaften der Universität Würzburg, Mittlerer Dallenbergweg 64, D-97082 Würzburg, Germany, , , , , , DE.
authors.forename: O L
authors.initials: OL
authors.lastname: Lange
authors.affiliation: Department of Biological Sciences, University of Waikato, Private Bag 3105, Hamilton, New Zealand, , , , , , NZ.
authors.forename: T G A
authors.initials: TG
authors.lastname: Green
authors.affiliation: Julius-von-Sachs-Institut für Biowissenschaften der Universität Würzburg, Mittlerer Dallenbergweg 64, D-97082 Würzburg, Germany, , , , , , DE.
authors.forename: H
authors.initials: H
authors.lastname: Reichenberger
authors.affiliation: Julius-von-Sachs-Institut für Biowissenschaften der Universität Würzburg, Mittlerer Dallenbergweg 64, D-97082 Würzburg, Germany, , , , , , DE.
authors.forename: S
authors.initials: S
authors.lastname: Hesbacher
authors.affiliation: Julius-von-Sachs-Institut für Biowissenschaften der Universität Würzburg, Mittlerer Dallenbergweg 64, D-97082 Würzburg, Germany, , , , , , DE.
authors.forename: P
authors.initials: P
authors.lastname: Proksch
keywords: Key words Lichen acid; Lichen; Lichen substances; Photosynthesis; Water content