Journal Article

Altitudinal changes in temperature responses of net photosynthesis and dark respiration in tropical bryophytes

Sebastian Wagner, Gerhard Zotz, Noris Salazar Allen and Maaike Y. Bader

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 111, issue 3, pages 455-465
Published in print March 2013 | ISSN: 0305-7364
Published online December 2012 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcs267
Altitudinal changes in temperature responses of net photosynthesis and dark respiration in tropical bryophytes

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Background and Aims

There is a conspicuous increase of poikilohydric organisms (mosses, liverworts and macrolichens) with altitude in the tropics. This study addresses the hypothesis that the lack of bryophytes in the lowlands is due to high-temperature effects on the carbon balance. In particular, it is tested experimentally whether temperature responses of CO2-exchange rates would lead to higher respiratory carbon losses at night, relative to potential daily gains, in lowland compared with lower montane forests.

Methods

Gas-exchange measurements were used to determine water-, light-, CO2- and temperature-response curves of net photosynthesis and dark respiration of 18 tropical bryophyte species from three altitudes (sea level, 500 m and 1200 m) in Panama.

Key Results

Optimum temperatures of net photosynthesis were closely related to mean temperatures in the habitats in which the species grew at the different altitudes. The ratio of dark respiration to net photosynthesis at mean ambient night and day temperatures did not, as expected, decrease with altitude. Water-, light- and CO2-responses varied between species but not systematically with altitude.

Conclusions

Drivers other than temperature-dependent metabolic rates must be more important in explaining the altitudinal gradient in bryophyte abundance. This does not discard near-zero carbon balances as a major problem for lowland species, but the main effect of temperature probably lies in increasing evaporation rates, thus restricting the time available for photosynthetic carbon gain, rather than in increasing nightly respiration rates. Since optimum temperatures for photosynthesis were so fine tuned to habitat temperatures we analysed published temperature responses of bryophyte species worldwide and found the same pattern on the large scale as we found along the tropical mountain slope we studied.

Keywords: Altitudinal gradient; bryophytes; carbon balance; dark respiration; gas-exchange measurements; hepatics; liverworts; mosses; net photosynthesis; photosynthesis-response curves; temperature; tropical rain forest

Journal Article.  7034 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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