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.     

Partitioning of CO2 Fixation in the Colonial Cyanobacterium Microcystis aeruginosa: Mechanism Promoting Formation of Surface Scums

Constraints on inorganic carbon (C_i) availability stimulated buoyancy in natural, photosynthetically active populations of the colonial blue-green alga (cyanobacterium) Microcystis aeruginosa. In nonmixed eutrophic river water and cultures, O₂ evolution determinations indicated C_i limitation of photosynthesis, which was overcome either by CO₂ additions to the aqueous phase or by exposure of buoyant colonies to atmospheric CO₂. Microautoradiographs of M. aeruginosa colonies revealed partitioning of ¹⁴CO₂ fixation and photosynthate accumulation between peripheral and internal cells, particularly in large colonies. When illuminated colonies were suspended in the aqueous phase, peripheral cells accounted for at least 90% of the ¹⁴CO₂ assimilation, whereas internal cells remained unlabeled. However, when ¹⁴CO₂ was allowed to diffuse into colonies 15 min before illumination, a more uniform distribution of labeling was observed. Resultant differences in labeling patterns were most likely due to peripheral cells more exclusively utilizing CO₂ when ambient C_i concentrations were low. Among colonies located at the air-water interface, internal cells showed an increased share of photosynthate production when atmospheric ¹⁴CO₂ was supplied. This indicated that C_i transport was restricted in large colonies below the water surface, forcing internal cells to maintain a high degree of buoyancy, thus promoting the formation of surface scums. At the surface, C_i restrictions were alleviated. Accordingly, scum formation appears to have an ecological function, allowing cyanobacteria access to atmospheric CO₂ when the C_i concentration is growth limiting in the water column.     

Diurnal and seasonal changes in the intensity of photosynthesis in stems of lilac (Syringa vulgaris L.)

It has been demonstrated that during the whole year the stems are photosyntheticaly active and capable of assimilating atmospheric CO₂. The intensity of photosynthesis varies. During the vegetation period the registered net photosynthesis lasted up to 13 hours per day, and in the leafless period for 2–3 hours a day. Photosynthesis was registered also at temperatures below zero (−3 °C) as a reduced CO₂ evolution in light in comparison with darkness. The maximal net photosynthesis values during the vegetation period amounted to 6 up 8 μmol (CO₂)·m⁻²·s⁻¹, and in the leafless period 0.5 – 1 μmol (CO₂)·m⁻²·s⁻¹, and they were close to being up to twice as big as the values obtained of darkness respiration. An increase of the photosynthetic activity of stems preceded the spring development of the leaves.     

DECREASED RATE OF GLUCOSE UTILIZATION BY RAT BRAIN IN VIVO AFTER EXPOSURE TO ATMOSPHERES CONTAINING HIGH CONCENTRATIONS OF CO2

—(1) The effects of exposure of rats to increased atmospheric concentrations of CO₂ on brain metabolism in vivo were studied. (2) After 2·5 min exposure to an atmosphere of 20% CO₂, the rate of glucose utilization by brain decreased from 0·61 μmol/min per g to 0·32 μmol/min per g and remained between 0·3 and 0·4 μmol/min per g for 60 min, the longest interval studied. O₂ utilization, calculated from the arteriovenous difference of O₂ across the brain and blood flow, was 3·5 μmol/min per g in controls and was 4·7 μmol/min per g after 5 min in the 20% CO₂ atmosphere. (3) The concentrations of glucose, glucose 6-phosphate and aspartate were increased during the first 10 min of CO₂ exposure whereas the concentrations of other glycolytic intermediates, tricarboxylic acid cycle intermediates and glutamate were decreased. The amount of endogenous substrate which disappeared during the first 10 min was sufficient, if used to supplement glucose as a fuel, to maintain the O₂ consumption at, or slightly above, the control level. Glutamate and lactate were quantitatively the most important energy sources. (4) The mechanism whereby‘CO₂ decreased the rate of glucose utilization is uncertain. The initial rise in glucose 6-phosphate and fall in fructose 1,6-diphosphate concentrations suggested that an inhibition of phosphofructokinase was responsible. However, after 60 min in 20% CO₂, the concentrations of both of these metabolites returned to normal while the rate of glucose utilization remained depressed.     

The effects of CO2, temperature and their interaction on the growth and yield of carrot (Daucus carota L.)

Stands of carrot (Daucus carota L.) were grown in the field within polyethylene-covered tunnels at a range of soil temperatures (from a mean of 7·5°C to 10·9°C) at either 348 (SE = 4·7) or 551 (SE = 7·7) μmol mol⁻¹ CO₂. The effect of increased atmospheric CO₂ concentration on root yield was greater than that on total biomass. At the last harvest (137d from sowing), total biomass was 16% (95% CI = 6%, 27%) greater at 551 than at 348 μmol mol⁻¹ CO₂, and 37% (95% CI = 30%, 44%) greater as a result of a 1°C rise in soil temperature. Enrichment with CO₂ or a 1°C rise in soil temperature increased root yield by 31% (95% CI = 19%, 45%) and 34% (95% CI = 27%, 42%), respectively, at this harvest. No effect on total biomass or root yield of an interaction between temperature and atmospheric CO₂ concentration at 137 DAS was detected. When compared at a given leaf number (seven leaves), CO₂ enrichment increased total biomass by 25% and root yields by 80%, but no effect of differences in temperature on plant weights was found. Thus, increases in total biomass and root yield observed in the warmer crops were a result of the effects of temperature on the timing of crop growth and development. Partitioning to the storage roots during early root expansion was greater at 551 than at 348 μmol mol⁻¹ CO₂. The root to total weight ratio was unaffected by differences in temperature at 551 μmol mol⁻¹CO₂, but was reduced by cooler temperatures at 348 μmol mol⁻¹ CO₂. At a given thermal time from sowing, CO₂ enrichment increased the leaf area per plant, particularly during early root growth, primarily as a result of an increase in the rate of leaf area expansion, and not an increase in leaf number.     

PRIMARY PRODUCTION,CALCIFICATION, AND AIR-SEA CO2 FLUXES OF A MACROALGAL-DOMINATED CORAL REEF COMMUNITY (MOOREA,FRENCH POLYNESIA)1

Community metabolism and air-sea carbon dioxide (CO₂) fluxes were investigated in July 1992 on a fringing reef at Moorea (French Polynesia). The benthic community was dominated by macroalgae (85% substratum cover) and comprised of Phaeophyceae Padina tenuis (Bory), Turbinaria ornata (Turner) J. Agardh, and Hydroclathrus clathratus Bory (Howe); Chlorophyta Halimeda incrassata f. ovata J. Agardh (Howe); and Ventricaria ventricosa J. Agardh (Olsen et West), as well as several Rhodophyta (Actinotrichia fragilis Forskál (Børgesen) and several species of encrusting coralline algae). Algal biomass was 171 g dry weight· m^?2. Community gross production (P_g), respiration (R), and net calcification (G) were measured in an open-top enclosure. P_g and R were respectively 248 and 240 mmol Co₂·m^?2·d^?1, and there was a slight net dissolution of CaCO₃ (0.8 mmol · m^?2·d^?1). This site was a sink for atmospheric CO₂ (10 ± 4 mmol CO₂·m^?2·d^?1), and the analysis of data from the literature suggests that this is a general feature of algal-dominated reefs. Measurement of air-sea CO₂ fluxes in open water close to the enclosure demonstrated that changes in small-scale hydrodynamics can lead to misleading conclusions. Net CO₂ evasion to the atmosphere was measured on the fringing reef due to changes in the current pattern that drove water from the barrier reef (a C0₂ source) to the study site.     

INORGANIC CARBON ACQUISITION BY CHRYSOPHYTES1

Twelve species, representing 12 families of the chrysophytes sensu lato, were tested for their ability to take up inorganic carbon. Using the pH‐drift technique, CO₂ compensation points generally varied between 1 and 20 μmol · L^?1 with a mean concentration of 5 μmol · L^?1. Neither pH nor alkalinity affected the CO₂ compensation point. The concentration of oxygen had a relatively minor effect on CO₂‐uptake kinetics, and the mean CO₂ compensation point calculated from the kinetic curves was 3.6 μmol · L^?1 at 10–15 kPa starting oxygen partial pressure and 3.8 μmol · L^?1 at atmospheric starting oxygen partial pressure (21 kPa). Similarly, uptake kinetics were not affected by alkalinity, and hence concentration of bicarbonate. Membrane inlet mass spectrometry (MIMS) in the presence and absence of acetazolamide suggested that external carbonic anhydrase in Dinobryon sertularia Ehrenb. and Synura petersenii Korschikov was either very low or absent. Rates of net HCO₃^? uptake were very low (～5% of oxygen evolution) using MIMS and decreased rather than increased with increasing HCO₃^? concentration, suggesting that it was not a real uptake. The CO₂ compensation points determined by MIMS for CO₂ uptake and oxygen evolution were similar to those determined in pH‐drift and were >1 μmol · L^?1. Overall, the results suggest that chrysophytes as a group lack a carbon‐concentrating mechanism (CCM), or an ability to make use of bicarbonate as an alternative source of inorganic carbon. The possible evolutionary and ecological consequences of this are briefly discussed.     

The effects of host carbon dioxide, nitrogen and water supply on the infection of wheat by powdery mildew and aphids

In two experiments, winter wheat (Triticum aestivum cv. Cerco) was grown in 350 (ambient) and 700 μmol mol^-1 (elevated) atmospheric CO₂ concentrations. In the first experiment, plants were grown at five levels of nitrogen fertilization, and in the second experiment, plants were grown at three levels of water supply. All plants were infected with powdery mildew, caused by the fungus Erysiphe graminis. Plants grown in elevated atmospheric CO₂ concentrations had significantly reduced % shoot nitrogen contents and significantly increased % shoot water contents. At elevated atmospheric CO₂ concentrations, where plant nitrogen content was significantly reduced, the severity of mildew infection was significantly reduced, and where host water content was significantly increased, the severity of mildew infection was significantly increased. In a moderate water supply treatment, the plants grown in elevated atmospheric CO₂ concentrations had significantly reduced nitrogen contents (9·9%) and significantly increased water content (4%), the amount of mildew infection was unchanged. The severity of mildew infection appeared to be more sensitive to host water content than to host nitrogen content.     

Photosynthesis, light and nitrogen relationships in a young deciduous forest canopy under open-air CO2 enrichment

Leaf photosynthesis (Ps), nitrogen (N) and light environment were measured on Populus tremuloides trees in a developing canopy under free‐air CO₂ enrichment in Wisconsin, USA. After 2 years of growth, the trees averaged 1·5 and 1·6 m tall under ambient and elevated CO₂, respectively, at the beginning of the study period in 1999. They grew to 2·6 and 2·9 m, respectively, by the end of the 1999 growing season. Daily integrated photon flux from cloud‐free days (PPFD_day,sat) around the lowermost branches was 16·8 ± 0·8 and 8·7 ± 0·2% of values at the top for the ambient and elevated CO₂ canopies, respectively. Elevated CO₂ significantly decreased leaf N on a mass, but not on an area, basis. N per unit leaf area was related linearly to PPFD_day,sat throughout the canopies, and elevated CO₂ did not affect that relationship. Leaf Ps light‐response curves responded differently to elevated CO₂, depending upon canopy position. Elevated CO₂ increased Ps_sat only in the upper (unshaded) canopy, whereas characteristics that would favour photosynthesis in shade were unaffected by elevated CO₂. Consequently, estimated daily integrated Ps on cloud‐free days (Ps_day,sat) was stimulated by elevated CO₂ only in the upper canopy. Ps_day,sat of the lowermost branches was actually lower with elevated CO₂ because of the darker light environment. The lack of CO₂ stimulation at the mid‐ and lower canopy was probably related to significant down‐regulation of photosynthetic capacity; there was no down‐regulation of Ps in the upper canopy. The relationship between Ps_day,sat and leaf N indicated that N was not optimally allocated within the canopy in a manner that would maximize whole‐canopy Ps or photosynthetic N use efficiency. Elevated CO₂ had no effect on the optimization of canopy N allocation.     

Photomineralization in a boreal hydroelectric reservoir: a comparison with natural aquatic ecosystems

In order to evaluate the role of photochemistry in the carbon dioxide (CO₂) generation from a 10-year-old boreal reservoir, the photomineralization of dissolved organic matter (DOM) was assessed and compared to a boreal river as well as to boreal and temperate lakes during July and August, 2003. Sterile water samples were irradiated by sunlight over the whole photoperiod and subsequently analyzed for CO₂. Mean energy-normalized apparent photochemical yield of CO₂ (an index of DOM photoreactivity normalized for the energy absorbed by samples) was significantly higher in the reservoir (27.7 ± 13.0 mg CO₂·m⁻³·kJ⁻¹) and the boreal river (35.8 ± 2.3 mg CO₂·m⁻³·kJ⁻¹) than in the boreal lakes (15.5 ± 5.1 mg CO₂·m⁻³·kJ⁻¹). The DOM photoreactivity of the temperate lakes (20.9 ± 8.1 mg CO₂·m⁻³·kJ⁻¹) was not statistically different from any type of boreal water bodies. There was no significant difference in either the integrated photoproduction of CO₂ (273–433 mg CO₂·m⁻²·d⁻¹) or the potential photochemical contribution to CO₂ diffusive fluxes (56–92%) among these water bodies. DOM photoreactivity was significantly affected by the cumulative hydrological residence time (CHRT) when considering the whole data set. However, when considering only the boreal water bodies, iron (Fe) and manganese (Mn) also intervened. The fact that DOM photoreactivity was related to CHRT as well as to Fe and Mn concentrations, which are respectively permanent and long-lasting features of the reservoir, suggests that the photoproduction of CO₂ is not likely to decrease over time. This process may therefore play a substantial role in the long-term CO₂ emissions from boreal reservoirs during the summer, its potential contribution to CO₂ diffusive fluxes being estimated at 56 ± 29 %.     

Elevated atmospheric CO2 differentially affects needle chloroplast ultrastructure and phloem anatomy in Pinus palustris: interactions with soil resource availability

The response of forest species to increasing atmospheric CO₂, particularly under resource limitations, will require study in order to predict probable changes which may occur at the plant, community and ecosystem levels. Longleaf pine (Pinus palustris Mill.) seedlings were grown for 20 months at two levels of CO₂ (365 and 720 μol mol¹) in two levels of soil nitrogen (4 and 40 g m^?2), and with two levels of soil moisture (–0·5 and –1·5 MPa xylem pressure potential). Leaf tissue was collected in the spring (12 months exposure) and autumn (20 months exposure) and examined using transmission electron microscopy (TEM) and light microscopy. During early spring, elevated CO₂ magnified effects of N and water treatment on starch accumulation and in some cases contributed to altered organization of mesophyll chloroplasts. Disruption of chloroplast integrity was pronounced under elevated CO₂, low N and water stress. In autumn, needles contained little starch; however, chloroplasts grown under high CO₂ exhibited stress symptoms including increased plastoglobuli and shorter grana. A trend for reduced needle phloem cross-sectional area resulting from fewer sieve cells was also observed under elevated CO₂. These results suggest that, in nature, longleaf pine seedlings may not benefit from a doubling of CO₂, especially when soil resources are limiting.     

The influence of carbon dioxide-depletion on growth and sinking rate of two planktonic diatoms in culture

Growth in relation to CO₂-depletion and CO₂-enrichment was investigated for the freshwater diatoms Asterionella formosa and Fragilaria crotonensis in batch cultures. Algal concentration and pH were measured during growth cycles, and inorganic carbon quantities determined by potentiometric Gran titrations and from pH-alkalinity relationships. After the primary growth with CO₂-depletion and pH increase, successive CO₂-enrichments induced further such cycles and produced a final three- to fivefold increase in algal biomass over that of unenriched controls. The extent of CO₂-depletion, and pH rise, was greater in later cycles, indicative of some cellular adaptation. Values of pH reached 9·7 for Asterionella and 9·9 for Fragilaria. The lowest residual quantities of free CO₂ were 0·1 and 0·03 μmol 1^-1 for Asterionella and Fragilaria respectively, which were less than 0·05% of the corresponding residual quantities of total CO₂. The primary limitation of CO₂-uptake and growth was probably related to the concentration of free CO₂, given the relative excess of other major nutrients (N, P, Si) in he media used. Limited of CO₂-uptake could be restored without CO₂ additions if the CO₂ present was redistributed between its several forms (increasing free CO₂) by the addition of strong acid, although growth was still restricted.

Limitation of CO₂-uptake, either by CO₂-depletion or the addition of an inhibitor of photo-synthesis (DCMU), increased the sinking rate of Asterionella cells from 0·3 to 1 m day^-1. The possible ecological implications of CO₂-pH-growth and CO₂-pH-buoyancy relationships are discussed, which may contribute to the frequent paucity of diatoms during summer in manv productive lakes.     

CO2 flux in alpine wetland ecosystem on the Qinghai-Tibetan Plateau, China

Using the CO₂ flux data measured by the eddy covariance method in the northeast of Qinghai-Tibetan Plateau in 2005, we analyzed the carbon flux dynamics in relation to meteorological and biotic factors. The results showed that the alpine wetland ecosystem was the carbon source, and it emitted 316.02 gCO₂ · m⁻² to atmosphere in 2005 with 230.16 gCO₂ · m⁻² absorbed in the growing season from May to September and 546.18 gCO₂ · m⁻² released in the non-growing season from January to April and from October to December. The maximum of the averaged daily CO₂ uptake rates and release rates was (0.45 ± 0.0012) mgCO₂ · m⁻² · s⁻¹ (Mean ± SE) in July and (0.22 ± 0.0090) mgCO₂ · m⁻² · s⁻¹ in August, respectively. The averaged diurnal variation showed a single-peaked pattern in the growing season, but exhibited very small fluctuation in the non-growing season. Net ecosystem exchange (NEE) and gross primary production (GPP) were all correlated with some meteorological factors, and they showed a negatively linear correlation with aboveground biomass, while a positive correlation existed between the ecosystem respiration (R_es) and those factors.     

INTERACTIONS BETWEEN LIGHT,NH4+, AND CO2 IN BUOYANCY REGULATION OF ANABAENA FLOS-AQUAE (CYANOPHYCEAE)1

Buoyancy of the gas-vacuolate alga Anabaena flosaquae Brébisson was measured under various levels of light, NH₄⁺, and CO₂. At high irradiance (50 μE · m^?2·^?1) the alga was non-buoyant regardless of the availability of CO₂ and NH₄⁺. At low irradiance (≤10 μE · m ^?2· s^?1) buoyancy was controlled by the availability of NH₄⁺ and CO₂. When NH₄⁺ was abundant, algal buoyancy was high over a wide range of CO₂ concentrations. In the absence of NH₄⁺, algal buoyancy was reduced at high CO₂ concentrations, however as the CO₂ concentration declined below about 5 μmol · L^?1, algal buoyancy increased. These results help explain why gas vacuolate, nitrogen-fixing blue-green algae often form surface blooms in eutrophic lakes.     

INTERACTIVE EFFECTS OF IRRADIANCE AND CO2 ON CO2 FIXATION AND N2 FIXATION IN THE DIAZOTROPH TRICHODESMIUM ERYTHRAEUM (CYANOBACTERIA)1

The diazotrophic cyanobacteria Trichodesmium spp. contribute approximately half of the known marine dinitrogen (N₂) fixation. Rapidly changing environmental factors such as the rising atmospheric partial pressure of carbon dioxide (pCO₂) and shallower mixed layers (higher light intensities) are likely to affect N₂‐fixation rates in the future ocean. Several studies have documented that N₂ fixation in laboratory cultures of T. erythraeum increased when pCO₂ was doubled from present‐day atmospheric concentrations (～380 ppm) to projected future levels (～750 ppm). We examined the interactive effects of light and pCO₂ on two strains of T. erythraeum Ehrenb. (GBRTRLI101 and IMS101) in laboratory semicontinuous cultures. Elevated pCO₂ stimulated gross N₂‐fixation rates in cultures growing at 38 μmol quanta · m^?2 · s^?1 (GBRTRLI101 and IMS101) and 100 μmol quanta · m^?2 · s^?1 (IMS101), but this effect was reduced in both strains growing at 220 μmol quanta · m^?2 · s^?1. Conversely, CO₂‐fixation rates increased significantly (P < 0.05) in response to high pCO₂ under mid‐ and high irradiances only. These data imply that the stimulatory effect of elevated pCO₂ on CO₂ fixation and N₂ fixation by T. erythraeum is correlated with light. The ratio of gross:net N₂ fixation was also correlated with light and trichome length in IMS101. Our study suggests that elevated pCO₂ may have a strong positive effect on Trichodesmium gross N₂ fixation in intermediate and bottom layers of the euphotic zone, but perhaps not in light‐saturated surface layers. Climate change models must consider the interactive effects of multiple environmental variables on phytoplankton and the biogeochemical cycles they mediate.     

Combined effects of elevated CO2 and air temperature on carbon assimilation of Pinus taeda trees

Branches of 22-year-old loblolly pine (Pinus taeda, L.) trees growing in a plantation were exposed to ambient CO₂, ambient + 165 μmol mol^?1 CO₂ or ambient + 330 μmol mol^?1 CO₂ concentrations in combination with ambient or ambient + 2°C air temperatures for 3 years. Field measurements in the third year indicated that net carbon assimilation was enhanced in the elevated CO₂ treatments in all seasons. On the basis of A/C_i, curves, there was no indication of photosynthetic down-regulation. Branch growth and leaf area also increased significantly in the elevated CO₂ treatments. The imposed 2°C increase in air temperature only had slight effects on net assimilation and growth. Compared with the ambient CO₂ treatment, rates of net assimilation were ～1·6 times greater in the ambient + 165 μmol mol^?1 CO₂ treatment and 2·2 times greater in the ambient + 330 μmol mol^?1 CO₂ treatment. These ratios did not change appreciably in measurements made in all four seasons even though mean ambient air temperatures during the measurement periods ranged from 12·6 to 28·2°C. This indicated that the effect of elevated CO₂ concentrations on net assimilation under field conditions was primarily additive. The results also indicated that the effect of elevated CO₂ (+ 165 or + 330 μmol mol^?1) was much greater than the effect of a 2°C increase in air temperature on net assimilation and growth in this species.     

Photosynthetic acclimation to long-term exposure to elevated CO2 concentration in Pinus radiata D. Don. is related to age of needles

The effects of CO₂ enrichment on photosynthesis and ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco) in current year and 1-year-old needles on the same branch were studied on Pinus radiata D. Don. trees growing for 4 years in large, open-top chambers at ambient (36 Pa) and elevated (65 Pa) CO₂ partial pressures. At this age trees were 3·5–4 m tall. Measurements made late in the growing cycle (March) showed that photosynthetic rates at the growth CO₂ concentration [(pCO₂)_a] were lower in 1-year-old needles of trees grown at elevated CO₂ concentrations than in those of trees grown at ambient (pCO₂)_a. At elevated CO₂ concentrations V_cmax (maximum carboxylation rate) was reduced by 13% and J_max (RuBP regeneration capacity mediated by maximum electron transport rate) by 17%. This corresponded with photosynthetic rates at the growth (pCO₂)_a of 4·68 ± 0·41 μmol m^–2 s^–1 and 6·15 ± 0·46 μmol m^–2 s^–1 at 36 and 65 Pa, respectively (an enhancement of 31%). In current year needles photosynthetic rates at the growth (pCO₂)_a were 6·2 ± 0·72 μmol m^–2 s^–1 at 36 Pa and 10·15 ± 0·64 μmol m^–2 s^–1 at 65 Pa (an enhancement of 63%). The smaller enhancement of photosynthesis in 1-year-old needles at 65 Pa was accompanied by a reduction in Rubisco activity (39%) and content (40%) compared with that at 36 Pa. Starch and sugar concentrations in 1-year-old needles were not significantly different in the CO₂ treatments. There was no evidence in biochemical parameters for down-regulation at elevated (pCO₂)_a in fully fexpanded needles of the current year cohort. These data show that enhancement of photosynthesis continues to occur in needles after 4 years’ exposure to elevated CO₂ concentrations. Photosynthetic acclimation reduces the degree of this enhancement, but only in needles after 1 year of growth. Thus, responses to elevated CO₂ concentration change during the lifetime of needles, and acclimation may not be apparent in current year needles. This transitory effect is most probably attributable to the effects of developmental stage and proximity to actively growing shoots on sink strength for carbohydrates. The implications of such age-dependent responses are that older trees, in which the contribution of older needles to the photosynthetic biomass is greater than in younger trees, may become progressively more acclimated to elevated CO₂ concentration.     

Social and territorial behaviour of laboratory mice (Mus musculus L.) in small complex areas

Hierarchically organized colonies of five male Mus musculus of strain LACA/CFW were transferred to complex arenas of 1·3, 2·6, 3·8 or 5·2 m². Mice in the 1·3 m² areas subsequently had their living space increased by removal of a partition to 2·6, 3·8 or 5·2 m². Changes in dominance occurred in eight out of thirteen of the colonies; the dominant mouse occupied the majority of the floor area, but some subordinates formed small territories. The number of territories held by subordinates was greater in the larger areas. In colonies in which the living area was expaded, however, there was no increase in the number of territories formed.     

SHORT‐ AND LONG‐TERM EFFECTS OF ELEVATED CO2 ON PHOTOSYNTHESIS AND RESPIRATION IN THE MARINE MACROALGA HIZIKIA FUSIFORMIS (SARGASSACEAE,PHAEOPHYTA) GROWN AT LOW AND HIGH N SUPPLIES1

The short‐term and long‐term effects of elevated CO₂ on photosynthesis and respiration were examined in cultures of the marine brown macroalga Hizikia fusiformis (Harv.) Okamura grown under ambient (375 μL · L^?1) and elevated (700 μL · L^?1) CO₂ concentrations and at low and high N availability. Short‐term exposure to CO₂ enrichment stimulated photosynthesis, and this stimulation was maintained with prolonged growth at elevated CO₂, regardless of the N levels in culture, indicating no down‐regulation of photosynthesis with prolonged growth at elevated CO₂. However, the photosynthetic rate of low‐N‐grown H. fusiformis was more responsive to CO₂ enrichment than that of high‐N‐grown algae. Elevation of CO₂ concentration increased the value of K_1/2(Ci) (the half‐saturation constant) for photosynthesis, whereas high N supply lowered it. Neither short‐term nor long‐term CO₂ enrichment had inhibitory effects on respiration rate, irrespective of the N supply, under which the algae were grown. Under high‐N growth, the Q₁₀ value of respiration was higher in the elevated‐CO₂‐grown algae than the ambient‐CO₂‐grown algae. Either short‐ or long‐term exposure to CO₂ enrichment decreased respiration as a proportion of gross photosynthesis (Pg) in low‐N‐grown H. fusiformis. It was proposed that in a future world of higher atmospheric CO₂ concentration and simultaneous coastal eutrophication, the respiratory carbon flux would be more sensitive to changing temperature.     

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.