title: The advantage of growing on moss: facilitative effects on photosynthetic performance and growth in the cyanobacterial lichen Peltigera rufescens.
abstract: Facilitative effects and plant-plant interactions are well known for higher plants, but there is a lack of information about their relevance in cryptogams. Additional information about facilitative effects between bryophytes and lichens would be an important contribution to recent research on positive plant-plant interactions, as these can have striking influences not only on the organisation of early successional terrestrial communities but also on succession dynamics by kick-starting ecosystem development through the import of key nutrients. We investigated and quantified these mechanisms between Peltigera rufescens and its associated mosses. Moss-associated thalli had a different morphology that led to several benefits from the association. They had 66% higher net photosynthetic rate and, because the majority of the gas exchange of lichen thalli took place through the lower surface, there was a further increase as the CO(2) concentration was >25% higher beneath moss-associated thalli. Microclimatic measurements showed that mean light levels were substantially lower and temperature extremes slightly ameliorated for moss-associated thalli. As a consequence, desiccation was slower which is, together with an increase in thallus thickness and water storage, the reason for extended periods of optimal net photosynthesis for the moss-associated thalli. All these benefits combined to produce a growth rate of the moss-associated thalli which was significantly higher, twice that of non-associated thalli [0.75 ± 0.4 vs. 0.30 ± 0.1 mm/month (mean ± SD)]. This appears to be the first demonstration of a strong mechanistic basis for facilitative effects between lichens and bryophytes.
authors.affiliation: Plant Ecology and Systematics, University of Kaiserslautern, PO-Box 3049, 67653, Kaiserslautern, Germany. claudia.colesie@biologie.uni-kl.de
authors.forename: Claudia
authors.initials: C
authors.lastname: Colesie
authors.forename: Sarah
authors.initials: S
authors.lastname: Scheu
authors.forename: T G Allan
authors.initials: TG
authors.lastname: Green
authors.forename: Bettina
authors.initials: B
authors.lastname: Weber
authors.forename: Rainer
authors.initials: R
authors.lastname: Wirth
authors.forename: Burkhard
authors.initials: B
authors.lastname: Büdel
mesh_terms: D044002:Bryophyta / Q000502:physiology*; D000458:Cyanobacteria / Q000502:physiology*; D008011:Lichens / Q000254:growth & development*; D008834:Microclimate; D010788:Photosynthesis; D013559:Symbiosis