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Lichen carbon gain under tropical conditions: water relations and CO2 exchange of Lobariaceae species of a lower montane rainforest in Panama

Published online by Cambridge University Press:  09 September 2004

Otto L. LANGE
Affiliation:
Julius-von-Sachs-Institut für Biowissenschaften der Universität Würzburg, Lehrstuhl für Botanik II, Julius-von-Sachs-Platz 3, D-97082 Würzburg, Germany
Burkhard BÜDEL
Affiliation:
Fachbereich Biologie, Allgemeine Botanik, Universität Kaiserslautern, Postfach 3049, D-67653 Kaiserslautern, Germany
Angelika MEYER
Affiliation:
Julius-von-Sachs-Institut für Biowissenschaften der Universität Würzburg, Lehrstuhl für Botanik II, Julius-von-Sachs-Platz 3, D-97082 Würzburg, Germany
Hans ZELLNER
Affiliation:
Julius-von-Sachs-Institut für Biowissenschaften der Universität Würzburg, Lehrstuhl für Botanik II, Julius-von-Sachs-Platz 3, D-97082 Würzburg, Germany
Gerhard ZOTZ
Affiliation:
Botanisches Institut der Universität Basel, Schönbeinstraße 6, CH-4056 Basel, Switzerland Smithsonian Tropical Research Institute, Balboa, Panama

Abstract

Diel (24-h) time courses of microclimate, water relations, and CO2 exchange were measured under quasi-natural conditions at a forest edge in a lower montane, tropical rainforest in Panama for six Lobariaceae (Lobaria crenulata, L. dissecta, Pseudocyphellaria aurata, P. intricata, Sticta sublimbata, S. weigelii). Responses to experimentally controlled water content (WC), photosynthetic photon fluence rate (PPFR), and temperature were studied in most detail with P. aurata.

Photosynthesis was well adapted to high temperatures, and all species exhibited ‘shade plant’ characteristics with low light compensation points and low light saturation. Lobaria and Pseudocyphellaria species suffered from a strong depression of net photosynthesis (NP) at suprasaturating WC; suprasaturation depression was less in cyphellate Sticta species.

Photosynthetic capacity correlated with thallus nitrogen concentration, and maximal NP rates of the cyanobacterial Sticta species was 4 to 5 times higher than that of the green algal Lobaria species. However, high rates of NP were uncommon and brief events under natural conditions; the different environmental factors were rarely optimal simultaneously. Similar to earlier observations with other rainforest lichens, NP ceased during the period of highest irradiation on most days due to desiccation. During moist periods low light often limited carbon fixation, and high thallus hydration was often detrimental to NP. In spite of these limitations the maximal daily integrated net photosynthetic carbon income (ΣNP) was quite high especially for the Sticta species [17·3 and 24·1 mgC (gC)−1 day−1 for S. sublimbata and S. weigelii, respectively]. High nocturnal carbon loss, due to high night temperatures and continuous hydration, resulted in frequent negative diel carbon balances (ΣC) in all species. The average nocturnal carbon loss amounted to 83 and 70% ΣNP for P. aurata and P. intricata, respectively and to 64 and 59% of ΣNP for S. sublimbata and S. weigelii, respectively. Their average diel ΣC was as high as 3·7 and 5·3 mgC (gC)−1 day−1. In contrast, ΣC was much lower for the other species, it amounted to only 0·18 mgC (gC)−1 day−1 for L. crenulata. Thus, the Sticta species stood out amongst the species studied for their most successful adaptation of photosynthetic productivity to the habitat conditions in the lower montane rainforest.

Type
Research Article
Copyright
© British Lichen Society 2004

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