Library

Notes: Public sector white collar employees are a large and important part of the labour force. It is interesting, therefore, to look at the forces determining the pay of such workers, given the highly administered nature of the markets for their services, and at the operation of their negotiating procedures which have remained highly centralized at a time when there has been a growing tendency to move away from national bargaining. This paper looks at some aspects of the pay of one group of public employees – school teachers. The examination deals mainly with global aspects of teachers' pay, comparatively little attention being given to structural aspects of the problem. The discussion is confined to the full-time teaching force in England and Wales, though the growth in the number of part-time teachers and para-teaching personnel has been an important feature of the market in recent years.

Notes: Photosynthetic capacity and leaf properties of sun and shade leaves of overstorey sweetgum trees (Liquidambar styraciflua L.) were compared over the first 3 years of growth in ambient or ambient + 200 μL L−1 CO2 at the Duke Forest Free Air CO2 Enrichment (FACE) experiment. We were interested in whether photosynthetic down-regulation to CO2 occurred in sweetgum trees growing in a forest ecosystem, whether shade leaves down-regulated to a greater extent than sun leaves, and if there was a seasonal component to photosynthetic down-regulation. During June and September of each year, we measured net photosynthesis (A) versus the calculated intercellular CO2 concentration (Ci) in situ and analysed these response curves using a biochemical model that described the limitations imposed by the amount and activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Vcmax) and by the rate of ribulose-1,5-bisphosphate (RuBP) regeneration mediated by electron transport (Jmax). There was no evidence of photosynthetic down-regulation to CO2 in either sun or shade leaves of sweetgum trees over the 3 years of measurements. Elevated CO2 did not significantly affect Vcmax or Jmax. The ratio of Vcmax to Jmax was relatively constant, averaging 2·12, and was not affected by CO2 treatment, position in the canopy, or measurement period. Furthermore, CO2 enrichment did not affect leaf nitrogen per unit leaf area (Na), chlorophyll or total non-structural carbohydrates of sun or shade leaves. We did, however, find a strong relationship between Na and the modelled components of photosynthetic capacity, Vcmax and Jmax. Our data over the first 3 years of this experiment corroborate observations that trees rooted in the ground may not exhibit symptoms of photosynthetic down-regulation as quickly as tree seedlings growing in pots. There was a strong sustained enhancement of photosynthesis by CO2 enrichment whereby light-saturated net photosynthesis of sun leaves was stimulated by 63% and light-saturated net photosynthesis of shade leaves was stimulated by 48% when averaged over the 3 years. This study suggests that this CO2 enhancement of photosynthesis will be sustained in the Duke Forest FACE experiment as long as soil N availability keeps pace with photosynthetic and growth processes.

Notes: The effects of long-term CO2 enhancement and varying nutrient availability on photosynthesis and ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) were studied on loblolly pine (Pinus taeda L.) seedlings grown in two atmospheric CO2 partial pressures (35 and 65 Pa) and three nutrient treatments (low N, low P, and high N and P). Measurements taken in late autumn (November) after 2 years of CO2 enrichment and nutrient addition showed that photosynthetic rates were higher for plants grown at elevated CO2 only when they received supplemental N. Total rubisco activity and rubisco content decreased at elevated CO2, but there was an increase in activation state. At elevated CO2, proportionately less N was found in rubisco and more N was found in the light reaction components. These results demonstrate acclimation of photosynthetic processes to elevated CO2 through reallocation of N. Loblolly pine grown in nutrient conditions similar to native soils (low N availability) had lower needle N and chlorophyll content, lower total rubisco activity and content, and lower photosynthetic rates than plants grown at high N and P. This suggests that the magnitude of the photosynthetic response to a future, high-CO2 environment will be dependent on soil fertility in the system.

Notes: In this study the question whether the alternative respiratory pathway acts as an electron bypass for the cytochrome pathway under conditions of growth on limited phosphorus in leaves of bean (Phaseolus vulgaris L.), tobacco (Nicotiana tabacum L.) and Gliricidia sepium Walp was investigated. The oxygen isotope fractionation technique was used to assess the in vivo activities of the cytochrome and alternative respiratory pathways in the absence of added inhibitors. The response of respiration to low phosphorus supply varied among species. Growth at low phosphorus reduced cytochrome pathway activity in bean and tobacco. Alternative pathway activity increased only in bean leaves in response to low phosphorus and not in tobacco. In the case of G. sepium, cytochrome pathway activity remained unchanged whereas the alternative pathway activity increased with low nutritional phosphorus. At low phosphorus, alternative oxidase protein levels increased in the leaves of bean and G. sepium but not in tobacco, suggesting a dependence of alternative pathway activity on protein level. Alternative pathway activity was also not correlated with soluble carbohydrate concentration in bean or tobacco at any phosphorus level. These results show that the alternative pathway does not always act as an electron bypass in response to the downstream restriction of the cytochrome pathway imposed by low phosphorus supply. These results suggest that factors in addition to cellular carbohydrate level and adenylate control can act to regulate alternative pathway activity.

Notes: Forest trees are major components of the terrestrial biome and their response to rising atmospheric CO2 plays a prominent role in the global carbon cycle. In this study, loblolly pine seedlings were planted in the field in recently disturbed soil of high fertility, and CO2 partial pressures were maintained at ambient CO2 (Amb) and elevated CO2 (Amb + 30 Pa) for 4 years. The objective of the study was to measure seasonal and long-term responses in growth and photosynthesis of loblolly pine exposed to elevated CO2 under ambient field conditions of precipitation, light, temperature and nutrient availability. Loblolly pine trees grown in elevated CO2 produced 90% more biomass after four growing seasons than did trees grown in ambient CO2. This large increase in final biomass was primarily due to a 217% increase in leaf area in the first growing season which resulted in much higher relative growth rates for trees grown in elevated CO2. Although there was not a sustained effect of elevated CO2 on relative growth rate after the first growing season, absolute production of biomass continued to increase each year in trees grown in elevated CO2 as a consequence of the compound interest effect of increased leaf area on the production of more new leaf area and more biomass. Allometric analyses of biomass allocation patterns demonstrated size-dependent shifts in allocation, but no direct effects of elevated CO2 on partitioning of biomass. Leaf photosynthetic rates were always higher in trees grown in elevated CO2, but these differences were greater in the summer (60–130% increase) than in the winter (14–44% increase), reflecting strong seasonal effects of temperature on photosynthesis. Our results suggest that seasonal variation in the relative photosynthetic response to elevated CO2 will occur in natural ecosystems, but total non-structural carbohydrate (TNC) levels in leaves indicate that this variation may not always be related to sink activity. Despite indications of canopy-level adjustments in carbon assimilation, enhanced levels of leaf photosynthesis coupled with increased total leaf area indicate that net carbon assimilation for the whole tree was greater for trees grown under elevated CO2 compared with ambient CO2. If the large growth enhancement observed in loblolly pine were maintained after canopy closure, then these trees could be a large sink for fossil carbon emitted to the atmosphere and produce a negative feedback on atmospheric CO2.

Notes: Elevated atmospheric carbon dioxide partial pressures have been shown to have variable direct and indirect effects on plant respiration rates. In this study, growth, leaf respiration, and leaf nitrogen and carbohydrate partitioning were measured in Gossypium hirsutum L. grown in 35 and 65 Pa CO2 for 30d. Growth and maintenance coefficients of leaf respiration were estimated using gas exchange techniques both at night and during the day. Elevated CO2 stimulated biomass production (107%) and net photo-synthetic rates (35–50%). Total day-time respiration (Rd) was not significantly affected by growth CO2 partial pressure. However, night respiration (Rn) of leaves grown in 65 Pa CO2 was significantly greater than that of plants grown in 35 Pa CO2. Correlation of Rd and Rn with leaf expansion rates indicated that plants in both CO2 treatments had equivalent growth respiration coefficients but maintenance respiration was significantly greater in elevated CO2. Increased maintenance coefficients in elevated CO2 appeared to be related to increased starch accumulation rather than to changes in leaf nitrogen.

Notes: Cotton plants were grown in CO2-controlled growth chambers in atmospheres of either 35 or 65 Pa CO2. A widely accepted model of C3 leaf photosynthesis was parameterized for leaves from both CO2 treatments using non-linear least squares regression techniques, but in order to achieve reasonable fits, it was necessary to include a phosphate limitation resulting from inadequate triose phosphate utilization. Despite the accumulation of large amounts of starch (〉50 g m−2) in the high CO2 plants, the photosynthetic characteristics of leaves in both treatments were similar, although the maximum rate of Rubisco activity (Vcmax), estimated from A versus Ci response curves measured at 29°C, was ∼10% lower in leaves from plants grown in high CO2. The relationship between key model parameters and total leaf N was linear, the only difference between CO2 treatments being a slight reduction in the slope of the line relating Vcmax to leaf N in plants grown at high CO2. Stomatal conductance of leaves of plants grown and measured at 65 Pa CO2 was approximately 32% lower than that of plants grown and measured at 35 Pa. Because photosynthetic capacity of leaves grown in high CO2 was only slightly less than that of leaves grown in 35 Pa CO2, net photosynthesis measured at the growth CO2, light and temperature conditions was approximately 25% greater in leaves of plants grown in high CO2, despite the reduction in leaf conductance. Greater assimilation rate was one factor allowing plants grown in high CO2 to incorporate 30% more biomass during the first 36 d of growth.