Water velocities around water plants in chalk streams

Water velocities were measured around water plants in a chalk stream. Low velocities (<100 mm.s^?1) were associated with stands of plants while faster flowing water (>500 mm.s^?1) was found in open water and above weed beds. An indirect method of estimating mean water velocity through weed beds, using discharge measurements, revealed velocities between 40 and 140 mm.s^?1, while open water velocities ranged between 200 and 370 mm.s^?1. The significance of the velocities is discussed.     

EFFECTS OF FLOWING WATER ON NITROGEN- AND PHOSPHORUS-LIMITED PHOTOSYNTHESIS AND OPTIMUM N:P RATIOS BY SPIROGYRA FLUVIATILIS (CHAROPHYCEAE)1,2

The effects of flowing water on net photosynthesis, dark respiration, specific growth rate, and optimum N:P ratios by Spirogyra fluviatilis Hilse were assessed. The alga was cultivated under nitrogen or phosphorus limitation in laboratory streams at three flow velocities: 3, 12, and 30 cm·s^?1. The Droop equation adequately described respiration and photosynthesis (PS_net) as a function of N or P cell quota (Q^N or Q^p). The data show that for N- or P-limited Spirogyra fluviatilis, flowing water is physiologically costly. Generally, flowing water had little effect on respiration rates; however, the proportion of gross photosynthesis devoted to dark respiration did increase with flow velocity. For photosynthesis, the minimum N and P cell quotas increased with velocity, and the theoretical PS_net maxima for N and P both appeared greatest at 12 cm·s^?1. The Droop models showed that for any given Q^N or Q^p, PS_net, was reduced by the 30-cm·s^?1 treatment. Consistent with this finding, independent estimates of specific growth rates for P-limited S. fluviatilis in the laboratory streams were inversely related to flow velocity when ambient PO₄^?3 was undetectable. However, growth was not diminished at the fastest velocity when PO₄^?3 was available for uptake. Thus, the increase in cellular phosphorus demand can be offset by flow-enhanced P uptake when conditions permit; otherwise, growth will be impaired. The optimum N:P ratios for S. fluviatilis at 3, 12, and 30 cm·s^?1 were 50, 58, and 52 by atoms, respectively, when calculated for PS_net= 0. The optimum ratios were inversely related to PS_net and decreased to approximately 20 when PS_net was near maximum. The potential for flowing water to mediate nutrient partitioning among lotic algae by altering growth rates and optimum nutrient ratios is discussed.     

PHOTOSYNTHESIS OF TWO MORPHOLOGIES OF NOSTOC PARMELIOIDES (CYANOBACTERIA) AS RELATED TO CURRENT VELOCITIES AND DIFFUSION PATTERNS1

Colonies of the stream-inhabiting cyanobacterium Nostoc parmelioides Kützing often contain a single endosymbiotic dipteran larva Cricotopus nostocicola (Wirth), which induces a morphological change from small, spherical colonies to larger, ear-shaped colonies. At a current velocity of 0 cm · s^?1, whole colonies containing the midge showed overall rates of ¹⁴CO₂ uptake and nitrogenase activity that were higher than those when the midge was absent (sphere-shaped colonies). Spherical colonies incubated at current velocities of 5-10 cm · s^?1did not show higher rates of ¹⁴CO₂ or ¹⁵N₂ incorporation than those with the larvae (ear-shaped colonies). Ear-shaped colonies extended well into regions of higher current velocity, whereas spherical colonies did not. Photosynthesis of ear-shaped colonies was stimulated by increased current velocity, increased inorganic C and decreased O₂ concentrations. Moreover, levels of O₂ at the surface of midge-inhabited colonies decreased with increased current velocity. The morphological change induced by the larva is detrimental (lowers photosynthesis and N₂ fixation) in quiescent water but not at current velocities above 10 cm · s^?1. This is probably a result of higher diffusion of O₂ and CO₂ associated with the midge-induced morphology.     

Influence of mixing and shear stress on Chlorella vulgaris, Scenedesmus obliquus, and Chlamydomonas reinhardtii

Photosynthetic activity (PA) and growth of different microalgae species (Chlorella vulgaris, Scenedesmus obliquus, and Chlamydomonas reinhardtii) depends in addition to other factors on mixing (tip speed) and shear stress (friction velocity) and was studied in a stirring tank (microcosm). In order to detect cause–effect relationships for an increase in photosynthetic activity, experiments were conducted under different pH values (6.0–8.5) and CO₂ concentrations (0.038 and 4 % (v/v)). The PA was determined as the effective quantum yield by pulse amplitude modulation during a stepwise increase of the tip speed from 0 to 589 cm s^?1 (friction velocity: 0–6.05 cm s^?1) in short-term experiments. The increase caused a distinctive pattern of PA of each species. Compared to 0 cm s^?1, C. vulgaris and S. obliquus showed a 4.0 and 4.8 % higher PA at the optimum tip speed of 126 cm s^?1 (friction velocity of 2.09 cm s^?1) and a 48 and 71 % higher growth, respectively. At 203 cm s^?1, the PA dropped to the value of the unstirred control, while at 589 cm s^?1, the PA decreased of up to 7 and 8 %. In contrast, C. reinhardtii showed 7 % stronger growth at 126 cm s^?1, while the PA decreased about 15 % at an increase of tip speed to 589 cm s^?1. For all investigated microalgae, the pattern of PA and higher growth was not only explained by the main contributing factors like light supply, nutrient supply, and overcoming diffusion gradients. The results indicate that hydrodynamic forces have a stimulating effect on the physiological processes within the cells.     

Functional characteristics of a fruticose type of lichen, Stereocaulon foliolosum Nyl. in response to light and water stress

Stereocaulon foliolosum a fruticose type of lichen under its natural habitat is subjected to low temperature, high light conditions and frequent moisture stress due its rocky substratum. To understand as to how this lichen copes up with these stresses, we studied the reflectance properties, light utilization capacity and the desiccation tolerance under laboratory conditions. S. foliolosum showed light saturation point for photosynthesis at 390 μmol CO₂ m^?2 s^?1 and the light compensation point for photosynthesis at 64 μmol CO₂ m^?2 s^?1. Our experiments show that S. foliolosum has a low absorptivity (30–35 %) towards the incident light. The maximum rates of net photosynthesis and apparent electron transport observed were 1.9 μmol CO₂ m^?2 s^?1 and 45 μmol e^? m^?2 s^?1, respectively. The lichen recovers immediately after photoinhibition under low light conditions. S. foliolosum on subjecting to desiccation results in the decrease of light absorptivity and the reflectance properties associated with water status of the thalli show a change. During desiccation, a simultaneous decrease in photosynthesis, dark respiration and quenching in the fluorescence properties was observed. However, all the observed changes show a rapid recovery on rewetting the lichen. Our study shows that desiccation does not have a severe or long-term impact on S. foliolosum and the lichen is also well adapted to confront high light intensities.     

FLOW‐INDUCED MORPHOLOGICAL VARIATIONS AFFECT DIFFUSION BOUNDARY‐LAYER THICKNESS OF MACROCYSTIS PYRIFERA (HETEROKONTOPHYTA,LAMINARIALES)1

In slow mainstream flows (<4–6 cm · s^?1), the transport of dissolved nutrients to seaweed blade surfaces is reduced due to the formation of thicker diffusion boundary layers (DBLs). The blade morphology of Macrocystis pyrifera (L.) C. Agardh varies with the hydrodynamic environment in which it grows; wave‐exposed blades are narrow and thick with small surface corrugations (1 mm tall), whereas wave‐sheltered blades are wider and thinner with large (2–5 cm) edge undulations. Within the surface corrugations of wave‐exposed blades, the DBL thickness, measured using an O₂ micro‐optode, ranged from 0.67 to 0.80 mm and did not vary with mainstream velocities between 0.8 and 4.5 cm · s^?1. At the corrugation apex, DBL thickness decreased with increasing seawater velocity, from 0.4 mm at 0.8 cm · s^?1 to being undetectable at 4.5 cm · s^?1. Results show how the wave‐exposed blades trap fluid within the corrugations at their surface. For wave‐sheltered blades at 0.8 cm · s^?1, a DBL thickness of 0.73 ± 0.31 mm within the edge undulation was 10‐fold greater than at the undulation apex, while at 2.1 cm · s^?1, DBL thicknesses were similar at <0.07 mm. Relative turbulence intensity was measured using an acoustic Doppler velocimeter (ADV), and overall, there was little evidence to support our hypothesis that the edge undulations of wave‐sheltered blades increased turbulence intensity compared to wave‐exposed blades. We discuss the positive and negative effects of thick DBLs at seaweed surfaces.     

Influence of light and temperature on photosynthesis and respiration by Pithophora oedogonia (Mont.) Wittr. (chlorophyceae)

Rates of net photosynthesis and respiration were determined for Pithophora oedogonia (Mont.) Wittr. acclimatized to 56 combinations of light (7–1200 μE m^?2 s^?1) and temperature (5–35°C). Conditions for maximum net photosynthesis were estimated to be 26°C and 970 μE m^?2 s^?1. The rate of net photosyntheses varied considerably with temperature, with the maximum measured value (9.67 mg O₂ h^?1 g dry wt.^?1) occurring at 25°C. Respiration rate increased with temperature and the light received just prior to measurement. The maximum respiration rate (7.05 mg O₂ g^?1 h^?1) occurred at 30°C and 1200 μE m^?2 s^?1. Exposure of Pithophora to light levels of 600 or 1200 μE m^?2 s^?1 prior to determination of the respiration rate resulted in significantly elevated levels of oxygen consumption at temperatures ≥ 15°C. The relationship between light, temperature and photosynthesis and respiration were summarized as three-dimensional response surfaces.     

Effects of water velocity on photosynthesis and dark respiration in submerged stream macrophytes

The effects of flow velocities on dark respiration and net photosynthesis of eight submerged stream macrophytes were examined in a laboratory oxygen chamber. The shoots/leaves were exposed to saturating free-CO₂ concentrations and were attached basally so that they could move in the flowing water. Net photosynthesis declined by 34–61% as flow velocity increased from 1 to 8.6cm s^?1, while dark respiration increased 2.4-fold over the same range. The increase in dark respiration could only account for between 19 and 67% of the decrease in net photosynthesis. The relationship between flow velocity (U) and net photosynthesis (P) was described by: P=b×U^a. The exponent, a, varied from -0.20 to –0.48 and showed a negative correlation to the surface: volume (SA: V) ratio of the plants, i.e. species with high SA: V ratio were more sensitive to flow. In contrast, net photosynthesis of plants firmly attached to a supporting frame was not significantly affected by increasing flow velocity. This result indicates that the physical stress imposed on the plants by agitation or stretching in the flowing water is a key factor for the observed response.     

The carbon dioxide hydration activity of brush-border carbonic anhydrase from the dog kidney

The steady-state kinetic parameters for the hydration of CO₂ catalyzed by membrane-bound carbonic anhydrase from the renal brush-border of the dog are compared with the same parameters for water-soluble bovine erythrocyte carbonic anhydrase. For the membrane-bound enzyme, the turnover number k_cat is 6.5 × 10⁵ s^?1 and the Michaelis constant is 7.5 mm for CO₂ hydration at pH 7.4 and 25 °C. The corresponding constants for bovine carbonic anhydrase under these conditions are 6.3 × 10⁵ s^?1 and 15 mm (Y. Pocker and D.W. Bjorkquist (1977)Biochemistry16, 5698–5707). The rate constant for the transfer of a proton between carbonic anhydrase and buffer was determined from the dependence of the catalytic rate on the concentration of the buffers imidazole and N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid (Hepes); the value of 2 × 10⁸m^?1s^?1 describes this constant for both forms of carbonic anhydrase at pH 7.4. Furthermore, the pH dependence of the initial velocity of hydration of CO₂ in the range of pH 6.5 to 8.0 is identical for the membrane-bound and soluble enzyme at low buffer concentration (1–2 mm imidazole). We conclude that the membrane plays no detectable role in affecting the CO₂ hydration activity and that the active site of the renal, membrane-bound carbonic anhydrase is exposed to the aqueous phase.     

Photosynthesis, Photorespiration and Respiration of Detached Spruce Twigs as Influenced by Oxygen Concentration and Light Intensity

The effects of oxygen concentration and light intensity on the rates of apparent photosynthesis, true photosynthesis, photorespiration and dark respiration of detached spruce twigs were determined by means of an infra-red carbon dioxide analyzer (IRCA). A closed circuit system IRCA was filled with either 1 per cent of oxygen in nitrogen, air (21 % O₂) or pure oxygen (100 % O₂). Two light intensities 30 × 10³ erg · cm ^?2· s^?1 and 120 × 10³ erg · cm^?2· s^?1 were applied. It has been found that the inhibitory effect of high concentration of oxygen on the apparent photosynthesis was mainly a result of a stimulation of the rate of CO₂ production in light (photorespiration). In the atmosphere of 100 % O₂, photorespiration accounts for 66–80 per cent of total CO₂ uptake (true photosynthesis). Owing to a strong acceleration of photorespiration by high oxygen concentrations, the rate of true photosynthesis calculated as the sum of apparent photosynthesis and photorespiration was by several times less inhibited by oxygen than the rate of apparent photosynthesis. The rates of dark respiration were essentially unaffected by the oxygen concentrations used in the experiments. An increase in the intensity of light from 30 × 10³ erg · cm^?3· s^?1 to 120 · 10³ erg · cm^?2· s^?1 enhanced the rate of photorespiration in the atmospheres of 21 and 100 % oxygen but not in 1 % O₂. The rate of apparent photosynthesis, however, was little affected by light intensity in an atmosphere of 1 % oxygen.     

Simple oscillations in photosynthesis of higher plants

Illumination of leaves of Vicia faba L. provoked oscillations in the rates of CO₂ uptake and O₂ evolution. The oscillations were marked under anaerobic conditions, but were absent at 20% O₂. The minimum CO₂ concentration required for the appearance of oscillations was 600 μl · l^?1. The higher the CO₂ concentration, the stronger the oscillations. The effect of CO₂ concentration was saturated at 1000 μl CO₂ · l^?1. The period of the oscillations was 5–6 min at a light intensity of 80 nE · cm^?2 · s^?1 and became longer on lowering of the intensity. No oscillations appeared at intensities below 12 nE · cm^?2 · s^?1. Oscillations could also be generated by increasing the CO₂ concentration in the atmosphere during strong illumination under anaerobic conditions. The chlorophyl a fluorescence yield showed oscillations, similar in shape and frequency to those of photosynthesis, after such an environmental change. Oscillations were also observed in photosynthesis of other C₃ plants, Lycopersicon esulentum Mill and Glycine max Merrill, under the same conditions as those required for V. faba, but were absent for the C₄ plants, Zea mays and Amaranthus retroflexus L.     

Photosynthetic characteristics of Amaranthus tricolor,a C4 tropical leafy vegetable

The gas exchange characteristics are reported for Amaranthus tricolor, a C₄ vegetable amaranth of southeastern Asia. Maximum photosynthetic capacity was 48.3±1.0μmol CO₂ m^?2s^?1 and the temperature optimum was 35°C. The calculated intercellular CO₂ concentration at this leaf temperature and an incident photon flux (400–700 mm) of 2 mmol m^?2s^?1 averaged 208±14 μl l^?1, abnormally high for a C₄ species. The photosynthetic rate, intercellular CO₂ concentration, and leaf conductance all decreased with an increase in water vapor pressure deficit. However, the decrease in leaf conductance which resulted in a decrease in intercellular CO₂ concentration accounted for only one fourth of the observed decrease in photosynthetic rate as water vapor pressure deficit was increased. Subsequent measurements indicated that the depence of net photosynthesis on intercellular CO₂ concetration changed with water vapor pressure deficit.     

Response of <Emphasis Type="Italic">Tisochrysis lutea</Emphasis> [Prymnesiophycidae] to aeration conditions in a bench-scale photobioreactor

The effects of superficial gas velocity (U_gr), gas entrance velocity (ν), and bubble size on the growth of Tisochrysis lutea was investigated in 600-mL photobioreactors operated with airlift pumps. Superficial gas velocities, calculated from measured air flow rates, ranging from 7 to 93 mm s^?1 were created using a 1.6-mm diameter syringe. We tested the effects of sparger velocity over a range of 2.48 to 73.4 m s^?1 and the effects of bubble size by using two styles of air stones and an open glass pipette, which created a bubble sizes in the range of 0.5 to 5 mm. We calculated oxygen mass transfer coefficient, k_La, values for all experimental conditions. Cell growth increased linearly with increased superficial gas velocity and decreased with increased sparger velocity. Results indicated that smaller bubble size leads to some initial cell damage, but after time, the increased gas transfer as reflected by the k_La value produced higher growth than larger bubbles. Two mechanisms were observed to correlate with cell damage in T. lutea: increasing velocity at the sparger tip and bubble bursting at the surface. These results demonstrate a method to test sensitivity of T. lutea to aeration, which is important for the design of airlift systems.     

GROWTH,PHOTOSYNTHESIS AND MAINTENANCE METABOLIC COST IN THE DIATOM PHAEODACTYLUM TRICORNUTUM AT VERY LOW LIGHT LEVELS 1

The compensation point for growth of Phaeodactylum tricornutum Bohlin is less than 1 μmol. m^?2s^?1. Growth at low PFDs (<3.5 μmol. m^?2.s^?1) does not appear to reduce the maximum quantum efficiency of photosynthesis (ø_m) or to greatly inhibit the potential for light-saturated, carbon-specific photosynthesis (P_m^c). The value for ø_m in P. tricornutum is 0.10–0.12 mol O₂-mol photon^?1, independent of acclimation PFD between 0.75 and 200 μmol.m^?2.s^?1 in nutrient-sufficient cultures. P_m^c in cells of P. tricornutum acclimated to PFDs <3.5 μmol m^?2?s^?1 is approximately 50% of the highest value obtained in nutrient-sufficient cultures acclimated to growth-rate-saturating PFDs. In addition, growth at low PFDs does not severely restrict the ability of cells to respond to an increase in light level. Cultures acclimated to growth at lees than 1% of the light-saturated growth rate respond rapidly to a shift-up in PFD after a short initial lag period and achieve exponential growth rates of 1.0 d^?1 (65% of the light- and nutrient-saturated maximum growth rate) at both 40 and 200 μmol.m^?2.s^?1     

Roles of aorta,ostia and tracheae in heartbeat and respiratory gas exchange in pupae of Troides rhadamantus Staudinger 1888 and Ornithoptera priamus L. 1758 (Lepidoptera,Papilionidae)

In non-diapausing pupae of the two birdwing butterfly species Troides rhadamantus and Ornithoptera priamus (Lepidoptera, Papilionidae) heart activity and CO₂ release rates were measured simultaneously within the initial half of pupal development. Heartbeat patterns in these pupae consist of three different types of activity: Continuous forward-pulse periods of different duration with a frequency range of about 0.25–0.52 s⁻¹, continuous backward-pulse periods with lower frequencies (0.15–0.29 s⁻¹) and intermittent backward-pulse periods when short series of three to 10 single heartbeats at frequencies of 0.12–0.35 s⁻¹ alternated with heart pauses of 2–10 min. CO₂ release was discontinuous (CFO-type) from about four to 12 days after pupation in Troides rhadamantus and from about four to 18 days in Ornithoptera priamus. Mean CO₂ release rates were very low in both species (10–30 nmol g⁻¹ min⁻¹). After this period, heart pauses occurred more frequently, probably indicating the onset of metamorphosis and the beginning partial histolysis of the heart. Infrared-optical and thermometrical measurements of heartbeat indicated that haemolymph transport within the dorsal vessel in forward direction is more effective than in backward direction. This is deduced from the higher heartbeat frequency and heartbeat amplitude of the forward pulsations. Results from ultrasonic doppler velocimetry suggest that haemolymph flow velocity is highest during the relatively long diastasis of 2–3 s (30–40 mm s⁻¹), while minimum particle speed (about 20 mm s⁻¹) is at the end of systole and the beginning of diastole. This would mean that haemolymph velocity is highest between two consecutive peristaltic waves. In contrast to the haemolymph velocity, the speed of the peristaltic wave measured with the infrared transmission technique was lower (about 8.4–22 mm s⁻¹ in Troides, 10–23 mm s⁻¹ in Ornithoptera) and remained constant during forward pulse periods. During backward beating the speed was lower (8–20 mm s⁻¹ in Troides, 9–17 mm s⁻¹ in Ornithoptera) and decreased during backward pulse periods. During day two to seven in Troides and day three to nine in Ornithoptera, spiracular opening periods coincided with changes in heartbeat direction from backward to forward pulsations. A possible influence is the more efficient convective haemolymph mixing in the haemocoel during forward heartbeat. The mixing allows to bring the haemolymph in close contact with the tracheal system where the discharge of CO₂ takes place. Heartbeat may therefore serve for shortening the diffusion pathways for a rapid transition into the tracheal system during the open period of the spiracles.     

Current velocity influences the facilitation and removal of algae by stream grazers

The modification of flows in lotic ecosystems can have dramatic effects on abiotic and biotic processes and change the structure of basal trophic levels. In high-gradient streams, most of the biota are benthic, and decreased flow may homogenize and reduce benthic current velocity, potentially changing stream ecosystem function. Grazing by macroinvertebrates is an important component of stream function because grazers regulate energy flow from primary producers to higher trophic levels. We conducted an experiment to examine how macroinvertebrate grazers facilitated or removed algal biomass across a gradient of benthic current velocity (0–40 cm s^?1). We chose three grazers (Drunella coloradensis, Cinygmula spp., and Epeorus deceptivus) from a montane stream and conducted our experiment using 24 artificial stream channels that had three treatments: no grazers (control), single-grazer, and combined-grazer treatments. In the absence of grazers, algal biomass increased with benthic current velocity. Grazer treatments differed from the control in that more algal biomass was removed at higher velocities, whereas algal accrual was largely facilitated at low velocities. The transition from facilitation to removal ranged from 4.5 to 5.9 cm s^?1 for individual grazer treatments and occurred at 11.7 cm s^?1 for the combined-grazer treatment. Our data suggest that velocity plays a significant role in the facilitation and removal of algae by macroinvertebrate grazers. Additionally, the patterns revealed here could have general implications for algal accrual in systems where flow is reduced.     

Influence of dissolved oxygen on the nitrification kinetics in a circulating bed biofilm reactor

The influence of dissolved oxygen concentration on the nitrification kinetics was studied in the circulating bed reactor (CBR). The study was partly performed at laboratory scale with synthetic water, and partly at pilot scale with secondary effluent as feed water. The nitrification kinetics of the laboratory CBR as a function of the oxygen concentration can be described according to the half order and zero order rate equations of the diffusion-reaction model applied to porous catalysts. When oxygen was the rate limiting substrate, the nitrification rate was close to a half order function of the oxygen concentration. The average oxygen diffusion coefficient estimated by fitting the diffusion-reaction model to the experimental results was around 66% of the respective value in water. The experimental results showed that either the ammonia or the oxygen concentration could be limiting for the nitrification kinetics. The latter occurred for an oxygen to ammonia concentration ratio below 1.5–2 gO₂/gN-NH₄ ⁺ for both laboratory and pilot scale reactors. The volumetric oxygen mass transfer coefficient (k _L a) determined in the laboratory scale reactor was 0.017?s^?1 for a superficial air velocity of 0.02?m s^?1, and the one determined in the pilot scale reactor was 0.040?s^?1 for a superficial air velocity of 0.031?m?s^?1. The k _L a for the pilot scale reactor did not change significantly after biofilm development, compared to the value measured without biofilm.     

The effect of irradiance and temperature responses and the phenology of a native alga,Undaria pinnatifida (Laminariales), at the southern limit of its natural distribution in Japan

Phenology, irradiance, and temperature characteristics of an edible brown alga, Undaria pinnatifida (Laminariales), were examined from the southernmost natural population in Japan, both by culturing gametophytes and examining the photosynthetic activity of sporophytes using dissolved oxygen sensors and pulse amplitude-modulated chlorophyll fluorometer (IMAGING-PAM). Our surveys confirmed that sporophytes were present between winter and early summer, but absent by July. IMAGING-PAM experiments were used to measure maximum effective quantum yield (ΦII at 0 μmol photons m^?2 s^?1) for each of 14 temperatures (8–36 °C). Oxygen production was also determined over a coarser temperature gradient. Net photosynthesis and ΦII (at 0 μmol photons m^?2 s^?1) were observed to be temperature-dependent; the maximum ΦII was estimated to be 0.67, occurred at 21.2 °C, and was nearly identical to the optimal temperature of the net photosynthetic rate (21.7 °C). A net photosynthesis–irradiance (P–E) model revealed that saturation irradiance (E _k) was 119.5 μmol photons m^?1 s^?1, and the compensation irradiance (E _c) was 17.4 μmol photons m^?1 s^?1. Culture experiments on the gametophytes revealed that most individuals could not survive temperatures over 28 °C and that growth rates were severely inhibited. Based on our observations, temperatures greater than 20 °C are likely to influence photosynthetic activity and gametophyte survival, and therefore, it is possible that this species might become locally extinct if seawater temperatures in this region continue to rise.     

Effect of irradiance and temperature on the photosynthesis of a cultivated red alga,Pyropia tenera (= Porphyra tenera), at the southern limit of distribution in Japan

The effect of irradiance and temperature on the photosynthesis of the red alga, Pyropia tenera, was determined for maricultured gametophytes and sporophytes collected from a region that is known as one of the southern limits of its distribution in Japan. Macroscopic gametophytes were examined using both pulse‐amplitude modulated fluorometry and/or dissolved oxygen sensors. A model of the net photosynthesis–irradiance (P‐E) relationship of the gametophytes at 12°C revealed that the net photosynthetic rate quickly increased at irradiances below the estimated saturation irradiance of 46 μmol photons m^?2 s^?1, and the compensation irradiance was 9 μmol photons m^?2 s^?1. Gross photosynthesis and dark respiration for the gametophytes were also determined over a range of temperatures (8–34°C), revealing that the gross photosynthetic rates of 46.3 μmol O₂ mg_chl‐a^?1 min^?1 was highest at 9.3 (95% Bayesian credible interval (BCI): 2.3–14.5)°C, and the dark respiration rate increased at a rate of 0.93 μmol O₂ mg_chl‐a^?1 min^?1°C^?1. The measured dark respiration rates ranged from ?0.06 μmol O₂ mg_chl‐a^?1 min^?1 at 6°C to ?25.2 μmol O₂ mg_chl‐a^?1 min^?1 at 34°C. The highest value of the maximum quantum yield (Fv/Fm) for the gametophytes occurred at 22.4 (BCI: 21.5–23.3) °C and was 0.48 (BCI: 0.475–0.486), although those of the sporophyte occurred at 12.9 (BCI: 7.4–15.1) °C and was 0.52 (BCI: 0.506–0.544). This species may be considered well‐adapted to the current range of seawater temperatures in this region. However, since the gametophytes have such a low temperature requirement, they are most likely close to their tolerable temperatures in the natural environment.     

Altitudinal Change in the Photosynthetic Capacity of Tropical Trees: A Case Study from Ecuador and a Pantropical Literature Analysis

In tropical mountains, trees are the dominant life form from sea level to above 4,000-m altitude under highly variable thermal conditions (range of mean annual temperatures: <8 to >28°C). How light-saturated net photosynthesis of tropical trees adapts to variation in temperature, atmospheric CO₂ concentration, and further environmental factors, that change along elevation gradients, is not precisely known. With gas exchange measurements in mature trees, we determined light-saturated net photosynthesis at ambient temperature (T) and [CO₂] (A _sat) of 40 tree species from 21 families in tropical mountain forests at 1000-, 2000-, and 3000-m elevation in southern Ecuador. We tested the hypothesis that stand-level averages of A _sat and leaf dark respiration (R _D) per leaf area remain constant with elevation. Stand-level means of A _sat were 8.8, 11.3, and 7.2?μmol?CO₂?m^?2?s^?1; those of R _D 0.8, 0.6, and 0.7?μmol?CO₂?m^?2?s^?1 at 1000-, 2000-, and 3000-m elevation, respectively, with no significant altitudinal trend. We obtained coefficients of among-species variation in A _sat and R _D of 20–53% (n?=?10–16 tree species per stand). Examining our data in the context of a pan-tropical A _sat data base for mature tropical trees (c. 170 species from 18 sites at variable elevation) revealed that area-based A _sat decreases in tropical mountains by, on average, 1.3?μmol?CO₂?m^?2?s^?1?per?km altitude increase (or by 0.2?μmol?CO₂?m^?2?s^?1 per K temperature decrease). The A _sat decrease occurred despite an increase in leaf mass per area with altitude. Local geological and soil fertility conditions and related foliar N and P concentrations considerably influenced the altitudinal A _sat patterns. We conclude that elevation is an important influencing factor of the photosynthetic activity of tropical trees. Lowered A _sat together with a reduced stand leaf area decrease canopy C gain with elevation in tropical mountains.