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Allometric relationships among the dimensions of leaves and their cells hold across diverse eudicotyledons, but have remained untested in the leaves of grasses. We hypothesised that geometric (proportional) allometries of cell sizes across tissues and of leaf dimensions would arise due to the coordination of cell development and that of cell functions such as water, nutrient and energy transport, and that cell sizes across tissues would be associated with light‐saturated photosynthetic rate. We tested predictions across 27 globally distributed C3 and C4 grass species grown in a common garden. We found positive relationships among average cell sizes within and across tissues, and of cell sizes with leaf dimensions. Grass leaf anatomical allometries were similar to those of eudicots, with exceptions consistent with the fewer cell layers and narrower form of grass leaves, and the specialised roles of epidermis and bundle sheath in storage and leaf movement. Across species, mean cell sizes in each tissue were associated with light‐saturated photosynthetic rate per leaf mass, supporting the functional coordination of cell sizes. These findings highlight the generality of evolutionary allometries within the grass lineage and their interlinkage with coordinated development and function. Summary statement: Allometries among leaf cell sizes and of cell sizes with leaf dimensions and photosynthetic rate hold across grass species, supporting their basis in developmental and functional coordination. [ABSTRACT FROM AUTHOR]

Estimates of the effect of increased global atmospheric CO2 levels on oceanic primary productivity depend on the physiological responses of contemporary phytoplankton populations. However, microalgal populations will possibly adapt to rising CO2 levels in such a way that they become genetically different from contemporary populations. The unknown properties of these future populations introduce an undefined error into predictions of C pool dynamics, especially the presence and size of the biological C pump. To address the bias in predictions introduced by evolution, we measured the kinetics of CO2 uptake in populations of Chlamydomonas reinhardtii that had been selected for growth at high CO2 for 1000 generations. Following selection at high CO2, the populations were unable to induce high-affinity CO2 uptake, and one line had a lower rate of net CO2 uptake. We attribute this to conditionally neutral mutations in genes affecting the C concentrating mechanism (CCM). Lower affinity CO2 uptake, in addition to smaller population sizes, results in a significant reduction in net CO2 uptake of about 38% relative to contemporary populations under the same conditions. This shows how predictions about the properties of communities in the future can be influenced by the effect of natural selection. [ABSTRACT FROM AUTHOR]

Estimates of the effect of increased global atmospheric CO2 levels on oceanic primary productivity depend on the physiological responses of contemporary phytoplankton populations. However, microalgal populations will possibly adapt to rising CO2 levels in such a way that they become genetically different from contemporary populations. The unknown properties of these future populations introduce an undefined error into predictions of C pool dynamics, especially the presence and size of the biological C pump. To address the bias in predictions introduced by evolution, we measured the kinetics of CO2 uptake in populations of Chlamydomonas reinhardtii that had been selected for growth at high CO2 for 1000 generations. Following selection at high CO2, the populations were unable to induce high-affinity CO2 uptake, and one line had a lower rate of net CO2 uptake. We attribute this to conditionally neutral mutations in genes affecting the C concentrating mechanism (CCM). Lower affinity CO2 uptake, in addition to smaller population sizes, results in a significant reduction in net CO2 uptake of about 38% relative to contemporary populations under the same conditions. This shows how predictions about the properties of communities in the future can be influenced by the effect of natural selection. [ABSTRACT FROM AUTHOR]

ABSTRACT Physiological properties of photosynthesis were determined in the marine diatom, Phaeodactylum tricornutum UTEX640, during acclimation from 5% CO2 to air and related to H2CO3 dissociation kinetics and equilibria in artificial seawater. The concentration of dissolved inorganic carbon at half maximum rate of photosynthesis (K0·5[DIC]) value in high CO2-grown cells was 1009 mmol m-3 but was reduced three-fold by the addition of bovine carbonic anhydrase (CA), whereas in air-grown cells K0·5[DIC] was 71 mmol m-3, irrespective of the presence of CA. The maximum rate of photosynthesis (Pmax) values varied between 300 and 500 μmol O2 mg Chl-1 h-1 regardless of growth pCO2. Bicarbonate dehydration kinetics in artificial seawater were re-examined to evaluate the direct HCO3- uptake as a substrate for photosynthesis. The uncatalysed CO2 formation rate in artificial seawater of 31·65°/oo of salinity at pH 8·2 and 25 °C was found to be 0·6 mmol m-3 min-1 at 100 mmol m-3 DIC, which is 53·5 and 7·3 times slower than the rates of photosynthesis exhibited in air- and high CO2-grown cells, respectively. These data indicate that even high CO2-grown cells of P. tricornutum can take up both CO2 and HCO3- as substrates for photosynthesis and HCO3- use improves dramatically when the cells are grown in air. Detailed time courses were obtained of changes in affinity for DIC during the acclimation of high CO2-grown cells to air. The development of high-affinity photosynthesis started after a 2–5 h lag period, followed by a steady increase over the next 15 h. This acclimation time course is the slowest to be described so far. High CO2-grown cells were transferred to controlled DIC conditions, at which the concentrations of each DIC species could be defined, and were allowed to acclimate for more than 36 h. The K0·5[DIC] values in acclimated cells appeared to be correlated only with [CO2(aq)] in the medium but not to HCO3-, CO32-, total [DIC] or the pH of the medium and indicate that the critical signal regulating the affinity of cells for DIC in the marine diatom, P. tricornutum, is [CO2(aq)] in the medium. [ABSTRACT FROM AUTHOR]