%0 Journal Article %1 Xiongetal_99 %A Xiong, F. S. %A Ruhland, C. T. %A Day, T. A. %D 1999 %J Physiologica Plantarum %K antarctic, bibtex-import, citeulikeExport gas\_exchange, honours, temperature %P 276--286 %T Photosynthetic temperature response of the Antarctic vascular plants @Colobanthus quitensis and @Deschampsia antarctica %V 106 %X The photosynthetic temperature response of the Antarctic vascular plants Colobanthus quitensis and Deschampsia antarctica was examined by measuring whole-canopy CO2 gas exchange and chlorophyll (Chl) a ?uorescence of plants grow- ing near Palmer Station along the Antarctic Peninsula. Both species had negligible midday net photosynthetic rates (Pn) on warm, usually sunny, days (canopy air temperature Tc \ 20C), but had relatively high Pn on cool days (Tc B 10C). Laboratory measurements of light and temperature responses of Pn showed that high temperature, not visible irradiance, was responsible for depressions in Pn on warm sunny days. The optimal leaf temperatures (Tl) for Pn in C. quitensis and D. antarctica were 14 and 10C, respectively. Both species had substantial positive Pn at 0C Tl, which were 28 (C. quitensis) and 32\% (D. antarctica) of their maximal Pn, and we estimate that their low-temperature compensation points occurred at ?2C Tl (C. quitensis) and ?3C (D. antarc- tica). Because of the strong warming trend along the peninsula over recent decades and predictions that this will continue, we were particularly interested in the mechanisms responsible for their negligible rates of Pn on warm days and their unusually low high-temperature compensation points (i.e., 26C in C. quitensis and 22C in D. antarctica). Low Pn at supraoptimal temperature (25C) appeared to be largely due to high rates of temperature-enhanced respiration. However, there was also evidence for direct impairment of the photosynthetic apparatus at supraoptimal temperature, based on Chl ?uorescence and Pn/intercellular CO2 concentration (ci) response curve analy- ses. The breakpoint or critical temperature (Tcr) of minimal ?uorescence (Fo) was : 42C in both species, which was well above the temperatures where reductions in Pn were evident, indicating that thylakoid membranes were structurally intact at supraoptimal temperatures for Pn. The optimal Tl for photochemical quenching (qp) and the quantum yield of photo- system II (PSII) electron transfer (FPSII) were 9 and 7C in C. quitensis and D. antarctica, respectively. Supraoptimal temperatures resulted in lower qp and greater non-photochem- ical quenching (qNP), but had little effect on Fo, maximal ?uorescence (Fm) or the ratio of variable to maximal ?uores- cence (Fv/Fm) in both species. In addition, carboxylation ef?ciencies or initial slopes of their Pn/ci response were lower at supraoptimal temperatures, suggesting reduced activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Although continued warming along the peninsula will increase the frequency of supraoptimal temperatures, Tc at our ?eld site averaged 4.3C and was below the temperature optima for Pn in these species for the majority of diurnal periods (86\%) during the growing season, suggesting that continued warming will usually improve their rates of Pn.

@article{Xiongetal_99, abstract = {{The photosynthetic temperature response of the Antarctic vascular plants Colobanthus quitensis and Deschampsia antarctica was examined by measuring whole-canopy CO2 gas exchange and chlorophyll (Chl) a ?uorescence of plants grow- ing near Palmer Station along the Antarctic Peninsula. Both species had negligible midday net photosynthetic rates (Pn) on warm, usually sunny, days (canopy air temperature [Tc] \ 20C), but had relatively high Pn on cool days (Tc B 10C). Laboratory measurements of light and temperature responses of Pn showed that high temperature, not visible irradiance, was responsible for depressions in Pn on warm sunny days. The optimal leaf temperatures (Tl) for Pn in C. quitensis and D. antarctica were 14 and 10C, respectively. Both species had substantial positive Pn at 0C Tl, which were 28 (C. quitensis) and 32\% (D. antarctica) of their maximal Pn, and we estimate that their low-temperature compensation points occurred at ?2C Tl (C. quitensis) and ?3C (D. antarc- tica). Because of the strong warming trend along the peninsula over recent decades and predictions that this will continue, we were particularly interested in the mechanisms responsible for their negligible rates of Pn on warm days and their unusually low high-temperature compensation points (i.e., 26C in C. quitensis and 22C in D. antarctica). Low Pn at supraoptimal temperature (25C) appeared to be largely due to high rates of temperature-enhanced respiration. However, there was also evidence for direct impairment of the photosynthetic apparatus at supraoptimal temperature, based on Chl ?uorescence and Pn/intercellular CO2 concentration (ci) response curve analy- ses. The breakpoint or critical temperature (Tcr) of minimal ?uorescence (Fo) was : 42C in both species, which was well above the temperatures where reductions in Pn were evident, indicating that thylakoid membranes were structurally intact at supraoptimal temperatures for Pn. The optimal Tl for photochemical quenching (qp) and the quantum yield of photo- system II (PSII) electron transfer (FPSII) were 9 and 7C in C. quitensis and D. antarctica, respectively. Supraoptimal temperatures resulted in lower qp and greater non-photochem- ical quenching (qNP), but had little effect on Fo, maximal ?uorescence (Fm) or the ratio of variable to maximal ?uores- cence (Fv/Fm) in both species. In addition, carboxylation ef?ciencies or initial slopes of their Pn/ci response were lower at supraoptimal temperatures, suggesting reduced activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Although continued warming along the peninsula will increase the frequency of supraoptimal temperatures, Tc at our ?eld site averaged 4.3C and was below the temperature optima for Pn in these species for the majority of diurnal periods (86\%) during the growing season, suggesting that continued warming will usually improve their rates of Pn.}}, added-at = {2019-03-31T01:14:40.000+0100}, author = {Xiong, F. S. and Ruhland, C. T. and Day, T. A.}, biburl = {https://www.bibsonomy.org/bibtex/284e4f4c6e7f3adc4002160e98a17fb8b/dianella}, citeulike-article-id = {1524132}, comment = {(private-note)fluorescence parameters temperature response negligible midday net photosynthetic rates 20°C relatively high Pn on cool days <10°C Topt 14 and 10oC for colobanthus and deschampsia respectively increased respiration accounted for high temperature compensation points Field measurements: no change in Ci with meas temperature... ie no change in stomatal limitation with temperature ie rubisco? measured at midday low rates on hot middays Lab measurements: There was no evidence of an increase in stomatal limitation of Pn at higher temperatures, as ci was not reduced with rising temp A Ci curves: Vc decreased at supraoptimal temperatures It looks to me like their J increased at 12oC a lot more than their Vc NO evidence of greater stomatal limitation at the supraoptimal temperature, as ls was lower at this temperature than at the optimal temperature in both species. For example, ls was only 0.17 at the supraoptimal temperature in both species, but was 0.25 at the optimal temperature in C. quitensis and 0.24 at the optimal temperature in D. antarctica. (relative stomatal limitation (ls) to Pn by the equation (Po-Pn)/Po, where Po is the Pn that would occur at a ca of 360 ml l-1 if resistance to CO2 diffusion were negligible (Farquhar and Sharkey 1982). they Suggest that as the temperature optimum for photosynthesis is above the average daytime temperature, warming will improve photosynthesis. ERRONEOUS! How do we make this clear to people?}, interhash = {6c646c091cd9682185b01f571db145fe}, intrahash = {84e4f4c6e7f3adc4002160e98a17fb8b}, journal = {Physiologica Plantarum}, keywords = {antarctic, bibtex-import, citeulikeExport gas\_exchange, honours, temperature}, pages = {276--286}, posted-at = {2007-07-31 07:40:19}, priority = {2}, timestamp = {2019-03-31T01:16:26.000+0100}, title = {{Photosynthetic temperature response of the Antarctic vascular plants @Colobanthus quitensis and @Deschampsia antarctica}}, volume = 106, year = 1999 }