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As previously described, the absolute rate of photosynthesis due to a limited concentration of dissolved inorganic carbon at alkaline pH, where the rate of CO2 formation is strictly limited, plotted as a function of chlorophyll (Chl) concentration, will take the form of a rectangular hyperbola combined with a linear rate directly proportional to [Chl], which are, respectively, due to the contribution of CO2 and HCO3– to photosynthesis. This model represents that the mathematical asymptote of absolute rate of photosynthesis versus cell density is described by the whole-cell rate constant for HCO3– uptake and the maximum rate of CO2 formation in the extracellular space. This means that any trace modification of the CO2 formation rate outside the cell will alter the photosynthetic rate and should be detectable experimentally. In air-grown Chlorella ellipsoidea and C. kessleri and in high CO2-grown C. saccharophila, the graph of the absolute rate of photosynthesis against [Chl] clearly followed the mathematical model described above and the actual CO2 formation rates outside the cells were not significantly different from the calculated rates. It also indicated that the whole-cell rate constants for CO2 and HCO3– uptake in air-grown C. ellipsoidea and C. saccharophila were similar at ≈ 300 and 2·0 mm3μg–1 Chl min–1, respectively, whereas those in air-grown C. kessleri were ≈ 550 and 15 mm3μg–1 Chl min–1. These results indicate that no acidification of the periplasmic space occurs, and there is no trace activity of external carbonic anhydrase in these microalgae.

External carbonic anhydrase (CA) activity in Chlorella saccharophila is suppressed by growth at high dissolved inorganic carbon and at acid pH. External CA activity was shown to be suppressed by growth at pHs below 7.0, with total repression at pH5.0. Growth in the presence of the buffer 3-[N-Morpholino]propane-sulphonic acid (MOPS) between pH 7 and 8 suppressed CA activity. Cells grown at pH8.0 aerated at 6 dm3 h−1 exhibited external CA activity of 5 units mg−1 Chl once the dissolved inorganic carbon (DIC) was reduced to 300 mmol m−3, and this increased to 30 units mg−1 Chl over a period of 3d while the DIC dropped to 30mmol m−3. Cells aerated at 180 dm3 h−1 showed a similar trend in CA activity, although the onset was delayed by 1 d and the DIC did not drop below 300 mmol m−3. Cells grown at pH 7.8 near an air equilibrium DIC of 300 mmol m−3had no detectable external CA activity. It is probable that it is the CO2 supply to the cell, and not total DIC or HCO−3 which controls external CA activity. Cells grown at pH 5.0 had no detectable activity, although they reduced the CO2 concentration to 0.6 mmol m−3. The loss of CA upon transfer of air-grown cells to 10 mmol mol−1 CO2 took place over 48 h and was light dependent, while the loss upon transfer from alkaline pH to acid pH look place over 12 h and was independent of light. The effects of pH are independent of the response to CO2.

The effects of conventional, bole only harvesting (CH) and whole-tree harvesting (WTH) on major inorganic nutrient concentrations (K, NO3-N, NH4-N, PO4-P and Ca) in soil water are described from Beddgelert forest in North Wales. Monitoring of nutrient leaching losses, and the timing thereof, from brash through the soil and into streams draining the CH areas allowed assessments to be made of the value of brash as a nutrient source for second rotation crops. Most of the K (around 100 kg ha-1) and one-third of the P (10 out of 30 kg ha-1) leached out of the brash lying on the CH plots within one year of felling. A pulse of K passed through the soil profile, but less than half this K reached the streams. In contrast, the P was immobilized in the soil. The lack of brash resulted in the absence of K and P pulses on the WTH plots. On the CH plots, brash was a net sink for inorganic-N for 3 years after felling. However, in both CH and WTH, a pulse of nitrate was observed in the soil and also in streams draining CH areas. The source of this nitrate may have been death of fine tree roots, followed by rapid mineralization and nitrification. Calculation of a nutrient budget for a complete crop rotation indicates that P and Ca losses in harvested material are likely to result in long-term depletion of these elements, and that the effects will be significantly more severe if WTH is practised.

The influence of forest development on soil solution and surface drainage water aluminium chemistry was investigated in Sitka spruce (Picea sitchensis) plantations in Wales. Comparisons with semi-natural grassland and moorland sites are described. A highly significant positive relationship was shown between increasing forest age and soilwater aluminium concentrations in the B horizons. Shortterm/episodic peaks in Al concentrations were strongly related to incidences of high concentrations of neutral, marine-derived, salts in the soilwater. Nitrification may be an important factor in soil acidification and the mobilization of Al in soilwaters beneath the older mature-forest plantations in Wales. Labile monomeric Al concentrations were largest in surface waters draining the oldest forestry plantations compared with younger forest catchments and moorland, although response to discharge of soilwater acidity to the surface waters at individual sites was dependent on the acid neutralizing capacity of the groundwater component of the surface waters.

External carbonic anhydrase (CA) was detected in whole cells of alkaline-grown Chlorella saccharophila but was suppressed by growth at acid pH or growth on elevated levels of CO2. Internal CA activity was measured potentiometrically as an increase in activity in cell extracts over that of intact cells. Cells grown under all conditions had equal levels of internal CA activity. Two isozymes were identified after electrophoretic separation of soluble proteins on cellulose acetate plates. The fast isozyme was found in cells grown under all conditions, whereas the slow isozyme was found only in cells grown at alkaline pH. Western blot analysis following sodium dodecyl sulfate-polyacrylamide gel electrophoresis using antibodies produced against the periplasmic form of CA from Chlamydomonas reinhardtii revealed a single band at 39 kD, which did not change in intensity between growth conditions and was associated only with proteins eluted from the fast band. The slow isozyme was inactivated by incubation of cell extract at 30[deg]C and by incubation in 10 mM dithiothreitol, whereas the internal form was unaffected. These results indicate that external and internal forms of CA differ in structure and their activities respond differently to environmental conditions.

The physiological role of chloroplastic carbonic anhydrase (CA) was examined by antisense suppression of chloroplastic CA (on average 8% of wild type) in Nicotiana tabacum. Photosynthetic gas-exchange characteristics of low-CA and wild-type plants were measured concurrently with short-term, on-line stable isotope discrimination at varying vapor pressure deficit (VPD) and light intensity. Low-CA and wild-type plants were indistinguishable in the responses of assimilation, transpiration, stomatal conductance, and intercellular CO2 concentration to changing VPD or light intensity. At saturating light intensity, low-CA plants had lower discrimination against 13CO2 than wild-type plants by 1.2 to 1.8[per mille (thousand) sign]. Consequently, tissue of the low-CA plants was higher in 13C than the control plants. It was calculated that low-CA plants had chloroplast CO2 concentrations 13 to 22 [mu]mol mol-1 lower than wild-type plants. Discrimination against C18O16O in low-CA plants was 20% of that of the wild type, confirming a role of chloroplastic CA in the mechanism of discrimination against C18O16O ([delta]C18O16O). As VPD increased, stomatal closure caused a reduction in chloroplastic C02 concentration, and since VPD and chloroplastic CO2 concentration act in opposing directions on [delta]C18O16O, no effect of VPD was seen on [delta]C18O16O.

An equation has been developed incorporating whole-cell rate constants for CO2 and HCO3- that describes accurately photosynthesis (Phs) in suspensions of unicellular algae at low dissolved inorganic carbon. At pH 8.0 the concentration of CO2 available to the algal cells depends on the rate of supply from, and the loss to, HCO3- and the rate of use by the cells. At elevated cell densities (>30 mg chlorophyll [Chl] L-1), at which CO2 use by the cells is high, the slope of a graph of absolute Phs versus Chl concentration approaches the rate of Phs on a milligram of Chl basis because of HCO3- use alone. The slope of a graph of Phs versus HCO3- will be the rate constant for HCO3-, and for Chlorella saccharophila it was 0.16 L mg-1 Chl h-1. The difference between the constants for dissolved inorganic carbon (measured in cells with external carbonic anhydrase) and HCO3-1 is the constant for CO2, which was 26 L mg-1 Chl h-1. This difference causes the half-saturation constant for Phs to increase 5- to 6-fold at high cell densities. The increase in CO2 use as a result of external carbonic anhydrase is described mathematically as a function of cell density.

An input-output budget for dissolved inorganic-N in a small forested catchment in North Wales is presented. From 1982 to 1990, bulk precipitation inputs averaged 10.3 kg ha(-1) year(-1), whereas throughfall inputs in 1983-1984 were 20.3 kg ha(-1) year(-1). Streamwater outputs were consistently larger than bulk precipitation inputs, averaging 14.6 kg ha(-1) year(-1). Inorganic-N in the forest stream was predominantly nitrate and concentrations were substantially higher than in a nearby moorland stream. Both streams showed seasonal trends in nitrate concentration, with highest concentrations occurring in summer in the forest stream but in winter in the moorland stream. Nitrate concentration in the forest stream increased with increasing soil temperature up to approximately 7 degrees C and decreased at higher temperatures. Nitrification is thought to be responsible for nitrate production at temperatures both below and above 7 degrees C, but root uptake becomes significant only at the higher temperatures. In the forest, dry deposition and cloudwater inputs of inorganic-N are responsible for increased nitrogen fluxes in throughfall compared with wet deposition. Mineralization and nitrification in excess of plant needs causes the organic soil horizons to act as a net source of dissolved inorganic-N. Nitrogen transformations in the soil lead to soil acidification at a rate of 1.0 keq ha(-1) year(-1).

The effect of histamine on the uptake of radiosulphate by gastric tissue and gastric juice in guinea pigs was investigated. Radioactivity was recorded 4 hours after the administration of S35-labelled sulphate to normal controls and to histamine-treated animals.The radioactivity of fractions considered to contain sulphated mucopolysaccharides was also investigated.The uptake of radiosulphate by gastric tissue and juice was significantly higher in histamine-treated animals than in control guinea pigs.The S35 uptake by gastric sulphomucopolysaccharides was considered to represent the concentration of isotope by mucous cells and its secretion. This selective uptake was also markedly effected by histamine.Histamine may be a stimulant of the gastric mucous cells under the experimental conditions described.

Thermal annealing of defects in single-crystal GaP after 300 keV Ne+ irradiation at about 110°K to a dose of 6 • 1013 ions/cm2 has been studied at 110–500 °K by use of 275keV -channeled protons by measurement of back-scattering and gallium and phosphorus characteristic X-ray yields. The Ne+ dose was insufficient to produce any completely amorphous layer. Results indicate significant annealing at about 110°K, some further annealing at 200-350 °K and rapid annealing almost to completion in an annealing stage centred at 400 K. During both the neon irradiation and annealing, identical normalised gallium and phosphorus X-ray yields were observed. It was also found that irradiation of GaP at 103°K with 275 keV protons to doses of ~1016 H+/cm2 (unchanneled) caused significant lattice disorder.