Optimum Temperature For Photosynthesis Research Articles

Photosynthetic performance of the red alga Solieria pacifica (Solieriaceae) from two different depths in the sublittoral waters of Kagoshima, Japan

Photosynthetic responses to photosynthetically active radiation (PAR) and temperature were examined in the red alga Solieria pacifica from deep (35 m) and shallow (5 m) portions of the sublittoral zone in Kagoshima, Japan. Dissolved oxygen sensors and pulse-amplitude modulated (PAM) fluorometry were used for the measurements of net photosynthesis, dark respiration rates, and photochemical efficiency. The photosynthetic performances of the deep- and shallow-water ecotypes provided substantial evidence of their adaptation to the ambient PAR and temperature conditions of their respective habitats. Both algal samples showed different temperature optima for photosynthesis: 19.5–19.9 °C for S. pacifica from Mageshima (MAG) and 18.6–27.0 °C for species from Yatsushiro Bay (YAT), that reflect the temperature ranges in the 35- and 5-m depths of the sublittoral zone, respectively. Maximum net photosynthetic rate (P max = 3.73 μg O2 gfw −1 min−1), compensation PAR (E c = 21 μmol photons m−2 s−1), and saturation PAR (E k = 131 μmol photons m−2 s−1) were higher in YAT S. pacifica than in MAG samples (P max = 1.55 μg O2 gfw −1 min−1, E c = 3 μmol photons m−2 s−1, E k = 15 μmol photons m−2 s−1), which can be attributed to the higher PAR levels experienced by the seaweeds occurring at depths of 5 m. The large depressions in effective quantum yields (Φ PSII) after chronic PAR exposures and failed recovery in maximum quantum yields (F v /F m) after dark acclimation of MAG S. pacifica suggest a greater tendency for photodamage in the deep-water ecotype. As for the shallow-water S. pacifica (YAT), complete recovery occurred only at 20 °C. Low temperature limitation may account for the decreased gross photosynthetic rates and delayed recovery of post-dark acclimation F v /F m of YAT S. pacifica at temperatures below their optimum, which can occur during winter.

Photosynthesis in vine leaves as a function of light intensity, temperature, and leaf age

Photosynthesis and respiration were measured in the laboratory with an infrared CO 2 analyser using attached leaves on Sultana vines growing either in the glasshouse or out of doors. At light saturation (2,500-3,000 f. c.) the photosynthetic rates approximated 8.5 and 10.5 mg CO/h/dm 2 with light compensation points of 50 and 125 f. c. respectively. The optimum temperature for photosynthesis was between 25 and 30° C. Age effects were examined using shoots from well established field vines. Small but rapidly expanding terminal leaves showed no net photosynthesis but had a high rate of dark respiration and a CO 2 compensation point above 300 ppm. With further expansion the leaves showed a steady increase in photosynthetic activity with a corresponding decline in dark respiration and CO 2 compensation point. The rate of photosynthesis again declined with the onset of senescence.

Temperature optima for growth and photosynthetic processes in Trebouxia erici isolated from an Antarctic lichen and cultivated in a temperature gradient

The temperature optimum for photosynthesis and growth of natural populations of Trebouxia erici isolated from an Antarctic lichen (Usnea antarctica) was determined using a long-term cultivation (26 days) at different temperatures. Several chlorophyll fluorescence parameters were used in T. erici cultivated in a liquid medium to assess the effect of cultivation temperature (0, 10, 20 and 30oC). Analysis of time courses of the capacity of photosynthetic processes in PS II (FV/FM), effective quantum yield of photosystem II (FPSII), relative fluorescence decline ratio (RFd), and quenching of background chlorophyll fluorescence (qF0) revealed that optimum temperature is between 10 to 20°C. Biomass production evaluated as a total chlorophyll production after 26 days of cultivation was maximal at 20°C. The results are discussed in relation to the data reported by other literature sources for Trebouxia sp. and other algae isolated from chlorolichens.

Optimization and evaluation of key photosynthesis parameters in forest ecosystems based on FLUXNET data and VPM model.

Gross primary productivity (GPP) plays an important role in global carbon cycle. Vegetation maximum light use efficiency (Δmax) is the key parameter for GPP simulation of terrestrial ecosystem. Based on the vegetation photosynthesis model (VPM) and the eddy covariance flux data at 40 stations from FLUXNET (179 site-years of data), we identified the key model parameters influencing the simulation of GPP with VPM through one-at-a-time (OAT) method. The cross validation method was employed to optimize the key model parameters and evaluate the model perfor-mance for global forest ecosystems. The results showed that the prediction of GPP was mostly affec-ted by Δmax, maximum temperature for photosynthesis (Tmax), and optimum temperature for photosynthesis (Topt). There were distinguishable differences for the key optimized parameters among different forest ecosystems. The optimized Δmax ranged from 0.05 to 0.08 μmol CO2·μmol-1 PAR (evergreen broad-leaved forest>evergreen coniferous forest>mixed forest>deciduous broad-leaved forest). The optimized Tmax ranged from 38 to 48 ℃,while Topt ranged from 18 to 22 ℃. With the optimized key parameters based on ecosystem types, the VPM was able to simulate the seasonal and inter-annual variations of GPP in four forest ecosystems.

The Effects of Day and Night Temperature on the Dry Matter Accumulation of Oriental Hybrid Lily ‘Siberia’ as they Relate to the Photosynthetic and Respiratory Characteristics

The net photosynthetic rate on a per-plant basis of the Oriental hybrid lily ‘Siberia’ was low at the leafing stage but increased rapidly at the visible flower bud and flowering stages. The range of 20 to 25°C was the optimum temperature for photosynthesis at the three plant developmental stages under PPFD of 700 to 850 μmol photons m-2 s-1. The respiration rate increased with the increasing temperature quadratically (in aerial plant parts) or exponentially (in underground parts). The ‘Siberia’ plants were grown under three day temperature (DT) conditions of 28°C, 24°C or 20°C, with a night temperature (NT) of 15°C or three NTs of 25°C, 20°C or 15°C, with DT of 25°C in the growth chambers. At the flowering stage, the plants grown under low DT of 20°C had a high dry weight (DW) of the total plant, flowers, bulb, and roots, and a high DW/fresh weight (FW) ratio of the leaves, stem, and bulb. The plants grown under low NT of 15°C had a high DW of the total plant and stem, and a high DW/FW ratio of the leaves and bulb. The plants that were grown under a low NT had a long stem length by the positive DIF effect, which was supported by sufficient dry mater accumulation. The plants grown under low DT of 20°C showed a high relative growth rate (RGR) and net assimilation rate (NAR) from planting to flowering, whereas the NT condition did not affect the RGR or NAR. Discipline: Horticulture Additional key words: cut flower quality, growth analysis, positive DIF effect

Temperature tolerance of western Baltic Sea Fucus vesiculosus – growth, photosynthesis and survival

Seaweeds provide important ecosystem services in coastal areas, and loss of these macrophytes due to anthropogenic global change and warming is a worldwide concern. Fucus vesiculosus L. (Phaeophyceae) is the most abundant and hence ecologically most important primary producer, carbon sink and habitat provider in the western Baltic Sea. Therefore, we used this keystone species to test phenotypic acclimation of physiological performance traits (growth, photosynthesis and metabolites) of F. vesiculosus apices in a well-defined and highly resolved temperature gradient (5–29°C), supported by highly temporally resolved measurements. Temperature requirements of growth and photosynthesis were evaluated in three weeks exposure experiments, and changing tolerance ranges for survival over time were determined. Fucus vesiculosus was able to grow and survive over a temperature range from 5 to 26°C without any injury or visible damage of the apical growing meristem over all three weeks. However, at higher water temperatures (≥27°C) growth rapidly decreased from day three onwards and progressive necrosis was observed at 28 and 29°C. Stress-induced decrease in growth rate was already indicated by the effective quantum yield of chlorophyll fluorescence of photosystem II (PSII) several days in advance. Optimal temperature for photosynthesis (24°C), measured as electron transport rate, was higher compared to that for growth (15–20°C). Accordingly, the concentration of mannitol, the main product of photosynthesis, increased with higher temperatures. Understanding physiological responses of keystone macroalgae with respect to temperature and time is important, because rising global temperatures and summer heat wave frequencies and duration may affect the ecological functions of F. vesiculosus in the western Baltic Sea.

Investigation of North American vegetation variability under recent climate: A study using the SSiB4/TRIFFID biophysical/dynamic vegetation model

AbstractRecent studies have shown that current dynamic vegetation models have serious weaknesses in reproducing the observed vegetation dynamics and contribute to bias in climate simulations. This study intends to identify the major factors that underlie the connections between vegetation dynamics and climate variability and investigates vegetation spatial distribution and temporal variability at seasonal to decadal scales over North America (NA) to assess a 2‐D biophysical model/dynamic vegetation model's (Simplified Simple Biosphere Model version 4, coupled with the Top‐down Representation of Interactive Foliage and Flora Including Dynamics Model (SSiB4/TRIFFID)) ability to simulate these characteristics for the past 60 years (1948 through 2008). Satellite data are employed as constraints for the study and to compare the relationships between vegetation and climate from the observational and the simulation data sets. Trends in NA vegetation over this period are examined. The optimum temperature for photosynthesis, leaf drop threshold temperatures, and competition coefficients in the Lotka‐Volterra equation, which describes the population dynamics of species competing for some common resource, have been identified as having major impacts on vegetation spatial distribution and obtaining proper initial vegetation conditions in SSiB4/TRIFFID. The finding that vegetation competition coefficients significantly affect vegetation distribution suggests the importance of including biotic effects in dynamical vegetation modeling. The improved SSiB4/TRIFFID can reproduce the main features of the NA distributions of dominant vegetation types, the vegetation fraction, and leaf area index (LAI), including its seasonal, interannual, and decadal variabilities. The simulated NA LAI also shows a general increasing trend after the 1970s in responding to warming. Both simulation and satellite observations reveal that LAI increased substantially in the southeastern U.S. starting from the 1980s. The effects of the severe drought during 1987–1992 and the last decade in the southwestern U.S. on vegetation are also evident from decreases in the simulated and satellite‐derived LAIs. Both simulated and satellite‐derived LAIs have the strongest correlations with air temperature at northern middle to high latitudes in spring reflecting the effect of these climatic variables on photosynthesis and phenological processes. Meanwhile, in southwestern dry lands, negative correlations appear due to the heat and moisture stress there during the summer. Furthermore, there are also positive correlations between soil wetness and LAI, which increases from spring to summer. The present study shows both the current improvements and remaining weaknesses in dynamical vegetation models. It also highlights large continental‐scale variations that have occurred in NA vegetation over the past six decades and their potential relations to climate. With more observational data availability, more studies with different models and focusing on different regions will be possible and are necessary to achieve comprehensive understanding of the vegetation dynamics and climate interactions.

Effects of internal conductance and Rubisco on the optimum temperature for leaf photosynthesis in Fallopia japonica growing at different altitudes

AbstractTo investigate mechanisms of adjustment of the optimum temperature for leaf photosynthesis in alpine plants, we compared the temperature responses of photosynthesis, internal conductance (gi), and the amounts of activated Rubisco (ε) in two Fallopia japonica populations growing at elevations of 100 m (K0100), and 2250 m (F2250). There was an obvious difference in photosynthesis at high temperatures between the two populations, although there was no significant difference in the CO2/O2 specificity of Rubisco. Optimum temperatures for photosynthesis were 25 and 30 °C in F2250 and K0100, respectively. The temperature response of ε was similar to that of photosynthesis. The mean values of ε decreased 25 % (F2250) and 24 % (K0100), for temperatures 5 °C above the optimum for photosynthesis. In contrast, gi exponentially increased with increasing temperature in both populations. There was no significant difference in gi between populations for any given temperature. In both populations, there were no changes in CO2 concentrations at the Rubisco active site, when temperatures were above the photosynthetic optimum temperature. This clearly shows that photosynthetic optimum temperatures were not affected by photosynthetic limitation of CO2 diffusing from intercellular air spaces to Rubisco. Furthermore, the atmospheric pressure had a minor effect on the temperature response of photosynthesis. Thus, the decrease in ε in response to elevated temperatures reduced the photosynthetic optimum temperature in highland population of F. japonica, which was adjusted to the habitat.

Are winter-active species vulnerable to climate warming? A case study with the wintergreen terrestrial orchid, Tipularia discolor.

In the eastern United States, winter temperature has been increasing nearly twice as fast as summer temperature, but studies of warming effects on plants have focused on species that are photosynthetically active in summer. The terrestrial orchid Tipularia discolor is leafless in summer and acquires C primarily in winter. The optimum temperature for photosynthesis in T. discolor is higher than the maximum temperature throughout most of its growing season, and therefore growth can be expected to increase with warming. Contrary to this hypothesis, experimental warming negatively affected reproductive fitness (number of flowering stalks, flowers, fruits) and growth (change in leaf area from 2010 to 2012) in T. discolor. Temperature in June-July was critical for flowering, and mean July temperature greater than 29 °C (i.e., 2.5 °C above ambient) eliminated reproduction. Warming of 1.2 °C delayed flowering by an average of 10 days and fruiting by an average of 5 days. Warming of 4.4 °C reduced relative growth rates by about 60%, which may have been partially caused by the direct effects of temperature on photosynthesis and respiration. Warming indirectly increased vapor pressure deficit (VPD) by 0.2-0.5 kPa, and leaf-to-air VPD over 1.3 kPa restricted stomatal conductance of T. discolor to 10-40% of maximum conductance. These results highlight the need to account for changes in VPD when estimating temperature responses of plant species under future warming scenarios. Increasing temperature in the future will likely be an important limiting factor to the distribution of T. discolor, especially along the southern edge of its range.

Photosynthetic Characteristics of Four Wild Dendrobium Species in China

Photosynthetic physiology of Dendrobium nobile, Dendrobium pendulum, Dendrobium chrysotoxum, and Dendrobium densiflorum was studied. A bimodal diurnal variation of the net photosynthetic rate (Pn) was observed in the four Dendrobium species with the first peak [5.09 to 6.06 μmol (CO2) per m−2·s−1] ≈1100 hr and the second peak [3.83 to 4.58 μmol (CO2) per m−2·s−1] at 1500 hr. No CO2 fixation was observed at night. For all four Dendrobium species, the light compensation point (LCP) was 5 to 10 μmol·m−2·s−1, light saturation point (LSP) ranged from 800 to 1000 μmol·m−2·s−1, apparent quantum yield (AQY) was 0.02, and CO2 compensation points (CCP) and saturation point (CSP) were 60 to 85 μmol·mol−1 and 800 to 1000 μmol·mol−1, respectively. Carboxylation efficiency (CE) values ranged from 0.011 to 0.020. The optimum temperature for photosynthesis was between 26 and 30 °C. The measurement of Pn seasonal variation indicated that July to August had the higher Pn for Dendrobium species. Additionally, the chlorophyll a/b (Chl a/b) ratios of the leaves were 2.77 to 2.89. Measurement of key enzymes in the photosynthetic pathway indicated relatively high Ribulose-1,5-bisphosphate carboxylase (RuBPCase) and glycolate oxidase (GO) activities but very low phosphoenolpyruvate carboxylase (PEPCase) activities. It suggested that these four Dendrobium species are typical semishade C3 plants.

Photosynthetic Performance of Marestail (<i>Hippuris vulgaris</i> Linn.) across a Water Temperature Gradient

we examined the photosynthetic responses of submerged marestail in three lakes using pulse amplitude modulated (PAM) fluorometry. Three lakes were studied across a gradient of water temperature, with low water temperature conditions in Grass Lake and Arrow Bamboo Lake, and higher water temperature in Five Colored Lake. In the field, electron transport rates (ETRmax) were measured as rapid light curves (RLCs) by in situ yield measurements. Submerged marestail showed higher photosynthetic activity in Five Colored Lake compared to the other lakes, a response consistent with the adaptation of marestail in Five Colored Lake to high water temperature. The optimal temperature for photosynthesis of submerged marestail in Jiuzhaigou is about 12 °C. These results indicate that in different lakes the function of these aquatic plants is associated with a diversity of place-dependent environmental conditions, especially water temperature that leads to pronounced differences in the plant’s ecophysiological reactions.

Modeling sugarcane yield with a process-based model from site to continental scale: uncertainties arising from model structure and parameter values

Abstract. Agro-land surface models (agro-LSM) have been developed from the integration of specific crop processes into large-scale generic land surface models that allow calculating the spatial distribution and variability of energy, water and carbon fluxes within the soil–vegetation–atmosphere continuum. When developing agro-LSM models, particular attention must be given to the effects of crop phenology and management on the turbulent fluxes exchanged with the atmosphere, and the underlying water and carbon pools. A part of the uncertainty of agro-LSM models is related to their usually large number of parameters. In this study, we quantify the parameter-values uncertainty in the simulation of sugarcane biomass production with the agro-LSM ORCHIDEE–STICS, using a multi-regional approach with data from sites in Australia, La Réunion and Brazil. In ORCHIDEE–STICS, two models are chained: STICS, an agronomy model that calculates phenology and management, and ORCHIDEE, a land surface model that calculates biomass and other ecosystem variables forced by STICS phenology. First, the parameters that dominate the uncertainty of simulated biomass at harvest date are determined through a screening of 67 different parameters of both STICS and ORCHIDEE on a multi-site basis. Secondly, the uncertainty of harvested biomass attributable to those most sensitive parameters is quantified and specifically attributed to either STICS (phenology, management) or to ORCHIDEE (other ecosystem variables including biomass) through distinct Monte Carlo runs. The uncertainty on parameter values is constrained using observations by calibrating the model independently at seven sites. In a third step, a sensitivity analysis is carried out by varying the most sensitive parameters to investigate their effects at continental scale. A Monte Carlo sampling method associated with the calculation of partial ranked correlation coefficients is used to quantify the sensitivity of harvested biomass to input parameters on a continental scale across the large regions of intensive sugarcane cultivation in Australia and Brazil. The ten parameters driving most of the uncertainty in the ORCHIDEE–STICS modeled biomass at the 7 sites are identified by the screening procedure. We found that the 10 most sensitive parameters control phenology (maximum rate of increase of LAI) and root uptake of water and nitrogen (root profile and root growth rate, nitrogen stress threshold) in STICS, and photosynthesis (optimal temperature of photosynthesis, optimal carboxylation rate), radiation interception (extinction coefficient), and transpiration and respiration (stomatal conductance, growth and maintenance respiration coefficients) in ORCHIDEE. We find that the optimal carboxylation rate and photosynthesis temperature parameters contribute most to the uncertainty in harvested biomass simulations at site scale. The spatial variation of the ranked correlation between input parameters and modeled biomass at harvest is well explained by rain and temperature drivers, suggesting different climate-mediated sensitivities of modeled sugarcane yield to the model parameters, for Australia and Brazil. This study reveals the spatial and temporal patterns of uncertainty variability for a highly parameterized agro-LSM and calls for more systematic uncertainty analyses of such models.

The peaked response of transpiration rate to vapour pressure deficit in field conditions can be explained by the temperature optimum of photosynthesis

Leaf transpiration rate (E) frequently shows a peaked response to increasing vapour pressure deficit (D). The mechanisms for the decrease in E at high D, known as the ‘apparent feed-forward response’, are strongly debated but explanations to date have exclusively focused on hydraulic processes. However, stomata also respond to signals related to photosynthesis. We investigated whether the apparent feed-forward response of E to D in the field can be explained by the response of photosynthesis to temperature (T), which normally co-varies with D in field conditions. As photosynthesis decreases with increasing T past its optimum, it may drive a decrease in stomatal conductance (gs) that is additional to the response of gs to increasing D alone. If this additional decrease is sufficiently steep and coupling between A and gs occurs, it could cause an overall decrease in E with increasing D. We tested this mechanism using a gas exchange model applied to leaf-scale and whole-tree CO2 and H2O fluxes measured on Eucalyptus saligna growing in whole-tree chambers. A peaked response of E to D was observed at both leaf and whole-tree scales. We found that this peaked response was matched by a gas exchange model only when T effects on photosynthesis were incorporated. We conclude that field-based studies of the relationship between E and D need to consider signals related to changing photosynthetic rates in addition to purely hydraulic mechanisms.

Influence of Environmental Factors on Carbon Dioxide Exchange in Biological Soil Crusts in Desert Areas

The influence of water and light on CO2 exchange in cyanobacteria, lichen, and moss crusts at five temperature levels under controlled laboratory conditions was explored using a portable photosynthesis system. Across the range of temperatures, average optimum water content values for cyanobacteria, lichen and moss crusts were 0.38 ± 0.17 mm, 0.92 ± 0.06 mm, and 2.10 ± 0.02 mm (mean ± SE), respectively, whereas the respective average light saturation points were 900 ± 23, 870 ± 45, and 1200 ± 32 µ mol m−2 s−1. Optimum temperatures for photosynthesis were 20–27°C, 15°C, and 20°C, respectively, with maximum photosynthetic rates for the three types of crust of 2.67 ± 0.09, 3.06 ± 0.08, and 6.62 ± 0.06 µ mol m−2 s−1, respectively, under these optimum temperatures. Based on the observed data and climate information, the potential net photosynthetic carbon sequestration rates were estimated at 5.16, 3.46, and 6.05 g C m−2 a−1, respectively. These results indicate that the range of environmental conditions required for photosynthetic carbon sequestration in biological soil crusts is wide. Furthermore, moss crusts covering the smallest distribution area made the greatest contribution of C to the soil ecosystem, followed by cyanobacteria crusts, which covered the largest area.

Do CO2, temperature, rainfall and elevation influence stomatal traits and leaf width in Melaleuca lanceolata across southern Australia?

Herbarium specimens and contemporary collections were used to investigate the effects of environment and CO2 concentration on stomatal density, stomatal size, maximum potential water loss through stomata (gwmax) and leaf width of Melaleuca lanceolata Otto in southern Australia. Variation in CO2 had no effect on stomatal size and density, or gwmax of M. lanceolata. In contrast, stomatal density was negatively correlated with annual rainfall and there were significant, positive relationships between both elevation and mean maximum temperature and stomatal density. There was also a positive relationship between gwmax and maximum temperature. Leaf width was negatively correlated with both maximum temperature and elevation. We suggest that the increase in stomatal density and gwmax with increasing maximum temperatures enhances the potential for evaporative cooling of M. lanceolata leaves. It could also allow plants to maximise opportunities for carbon fixation during the sporadic rainfall events that are typical of drier, northern regions. This occurs in conjunction with a narrowing of the leaves in warmer climates and higher elevations, which results in a decrease in the thickness of the boundary layer. This combination of smaller leaves and increased potential for evaporative cooling through increased stomatal density and gwmax would allow the leaf to stay closer to its optimal temperature for photosynthesis.

Acclimation of Photosynthetic Traits of Caragana Species to Desert Environment in Inner Mongolian Plateau

Caragana species are commonly distributed in desert regions. We hypothesized that the photosynthetic traits of desert Caragana species could acclimated well to the desert environments, which are characterized by high temperature, intense radiation, and low moisture. To test our hypothesis, we studied the responses of photosynthesis to light, temperature and humidity, and fluorescence parameters of four Caragana species from desert region and one Caragana species from steppe region in Inner Mongolian Plateau. The desert Caragana species had higher light compensation point, light saturation point, optimum temperature for photosynthesis, and lower optimum relative air humidity for photosynthesis than the steppe Caragana species, and their net photosynthesis rates (Pn) were higher under high temperature, intense sunlight, and low humidity. The nonphotochemical quenching efficiency (NPQ) and minimal fluorescence (Fo) of the desert Caragana species were higher, and the values of maximum fluorescence (Fm), maximum quantum yield (Fv/Fm), relative quantum yield (ΦPSII), and photochemical quenching coefficient (qP) were lower, except for C. korshinskii. The electron transport rate (ETR) of the desert Caragana species was greater or similar to that of C. microphylla. In summary, the photosynthetic traits of the desert Caragana species acclimated well to desert environment, although such acclimation might be still not sufficient. The order of photosynthetic acclimation of the four species to desert environment is: C. korshinskii > C. stenophylla > C. tibetica > C. roborovskyi.

Photosynthesis of temperate Eucalyptus globulus trees outside their native range has limited adjustment to elevated CO2 and climate warming

Eucalyptus species are grown widely outside of their native ranges in plantations on all vegetated continents of the world. We predicted that such a plantation species would show high potential for acclimation of photosynthetic traits across a wide range of growth conditions, including elevated [CO2] and climate warming. To test this prediction, we planted temperate Eucalyptus globulus Labill. seedlings in climate-controlled chambers in the field located >700 km closer to the equator than the nearest natural occurrence of this species. Trees were grown in a complete factorial combination of elevated CO2 concentration (eC; ambient [CO2] +240 ppm) and air warming treatments (eT; ambient +3 °C) for 15 months until they reached ca. 10 m height. There was little acclimation of photosynthetic capacity to eC and hence the CO2-induced photosynthetic enhancement was large (ca. 50%) in this treatment during summer. The warming treatment significantly increased rates of both carboxylation capacity (V(cmax)) and electron transport (Jmax) (measured at a common temperature of 25 °C) during winter, but decreased them significantly by 20-30% in summer. The photosynthetic CO2 compensation point in the absence of dark respiration (Γ*) was relatively less sensitive to temperature in this temperate eucalypt species than for warm-season tobacco. The temperature optima for photosynthesis and Jmax significantly changed by about 6 °C between winter and summer, but without further adjustment from early to late summer. These results suggest that there is an upper limit for the photosynthetic capacity of E. globulus ssp. globulus outside its native range to acclimate to growth temperatures above 25 °C. Limitations to temperature acclimation of photosynthesis in summer may be one factor that defines climate zones where E. globulus plantation productivity can be sustained under anticipated global environmental change.

Temperature response of photosynthesis in C3, C4, and CAM plants: temperature acclimation and temperature adaptation

Most plants show considerable capacity to adjust their photosynthetic characteristics to their growth temperatures (temperature acclimation). The most typical case is a shift in the optimum temperature for photosynthesis, which can maximize the photosynthetic rate at the growth temperature. These plastic adjustments can allow plants to photosynthesize more efficiently at their new growth temperatures. In this review article, we summarize the basic differences in photosynthetic reactions in C3, C4, and CAM plants. We review the current understanding of the temperature responses of C3, C4, and CAM photosynthesis, and then discuss the underlying physiological and biochemical mechanisms for temperature acclimation of photosynthesis in each photosynthetic type. Finally, we use the published data to evaluate the extent of photosynthetic temperature acclimation in higher plants, and analyze which plant groups (i.e., photosynthetic types and functional types) have a greater inherent ability for photosynthetic acclimation to temperature than others, since there have been reported interspecific variations in this ability. We found that the inherent ability for temperature acclimation of photosynthesis was different: (1) among C3, C4, and CAM species; and (2) among functional types within C3 plants. C3 plants generally had a greater ability for temperature acclimation of photosynthesis across a broad temperature range, CAM plants acclimated day and night photosynthetic process differentially to temperature, and C4 plants was adapted to warm environments. Moreover, within C3 species, evergreen woody plants and perennial herbaceous plants showed greater temperature homeostasis of photosynthesis (i.e., the photosynthetic rate at high-growth temperature divided by that at low-growth temperature was close to 1.0) than deciduous woody plants and annual herbaceous plants, indicating that photosynthetic acclimation would be particularly important in perennial, long-lived species that would experience a rise in growing season temperatures over their lifespan. Interestingly, across growth temperatures, the extent of temperature homeostasis of photosynthesis was maintained irrespective of the extent of the change in the optimum temperature for photosynthesis (T opt), indicating that some plants achieve greater photosynthesis at the growth temperature by shifting T opt, whereas others can also achieve greater photosynthesis at the growth temperature by changing the shape of the photosynthesis-temperature curve without shifting T opt. It is considered that these differences in the inherent stability of temperature acclimation of photosynthesis would be reflected by differences in the limiting steps of photosynthetic rate.

Ecophysiology and genetic structure of polar versus temperate populations of the lichen Cetraria aculeata

We studied polar and temperate samples of the lichen Cetraria aculeata to investigate whether genetical differences between photobionts are correlated with physiological properties of the lichen holobiont. Net photosynthesis and dark respiration (DR) at different temperatures (from 0 to 30 °C) and photon flux densities (from 0 to 1,200 μmol m(-2) s(-1)) were studied for four populations of Cetraria aculeata. Samples were collected from maritime Antarctica, Svalbard, Germany and Spain, representing different climatic situations. Sequencing of the photobiont showed that the investigated samples fall in the polar and temperate clade described in Fernández-Mendoza et al. (Mol Ecol 20:1208-1232, 2011). Lichens with photobionts from these clades differ in their temperature optimum for photosynthesis, maximal net photosynthesis, maximal DR and chlorophyll content. Maximal net photosynthesis was much lower in Antarctica and Svalbard than in Germany and Spain. The difference was smaller when rates were expressed by chlorophyll content. The same is true for the temperature optima of polar (11 °C) and temperate (15 and 17 °C) lichens. Our results indicate that lichen mycobionts may adapt or acclimate to local environmental conditions either by selecting algae from regional pools or by regulating algal cell numbers (chlorophyll content) within the thallus.

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

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 CO(2)-exchange rates would lead to higher respiratory carbon losses at night, relative to potential daily gains, in lowland compared with lower montane forests. Gas-exchange measurements were used to determine water-, light-, CO(2)- 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. 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 CO(2)-responses varied between species but not systematically with altitude. 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.