Physiological and Anatomical Aspects of Photosynthesis of Two Agrostis Species at a Sub‐Antarctic Island

Leaf anatomy, rates of photosynthesis, leaf N, chlorophyll, RuBP carboxylase and nitrate reductase were studied on the indigenous Agrostis magellanica Lam. and the invasive alien Agrostis stolonifera L. on Marion Island (46° 54′ S, 37° 45′ E). Leaves of A. magellanica were more deeply ridged, thicker and more sclerophyllus than those of A. stolonifera. Mesophyll cells of A. magellanica were larger but the number of cells per unit leaf area and the total area of chloroplast per unit leaf area were the same for the two species. Maximum CO2 assimilation rates for the two species did not differ (mean maxima of 9.5 and 9 μmol CO2 m−2s−1for A. magellanica and A. stolonifera respectively). At low photon flux densities, A. stolonifera showed a greater response of CO2 assimilation to photon flux density. A. magellanica exhibited temperature‐dependent photoinhibition. Leaf N, chlorophyll and RuBP carboxylase on a fresh or dry weight basis were higher in A. stolonifera but on a leaf area basis there was little difference between the species. The competitive ability of A. stolonifera on Marion Island may be related to its response to low photon flux densities or to its carbon allocation patterns (less sclerophyllous tissue means that a greater leaf area may be produced per unit carbon fixed). The lack of support tissue may limit it to sites partly sheltered from frequent gale force winds

Physiology of Salt Excretion in the Mangrove Avicennia marina (Forsk.) Vierh

Diurnal and long‐term excretion by leaves of Avicennia marina seedlings growing in aqueous culture was correlated with substrate salinity and transpiration. Excretion was greater in 100% than 50% seawater but the reverse was true for transpiration. The diurnal excretion pattern, with exudation minimal during the day and maximal during the night, showed a negative correlation with the daily transpiration pattern. The total amount of salt excreted, however, showed a positive correlation with the total amount of water transpired. Root and xylem sap salinities were linearly related to substrate salinity but leaf Na+ increased to a maximum, indicating that control of leaf salt content is at the foliar, rather than the root level

Root growth dependence on soil temperature for Opuntia ficus-indica: Influences of air temperature and a doubled CO\u3csub\u3e2\u3c/sub\u3e concentration

1. Root elongation as a function of soil temperature was determined for the CAM succulent Opuntia ficus-indica, under three different day/night air temperatures (15 °C/5 °C, 25 °C/15 °C and 35 °C/25 °C) and an ambient (360 μmol mol-1) vs a doubled CO2 concentration (720 μmol mol-1) at 25 °C/15 °C, the optimum temperature for net CO2 uptake. 2. Root elongation occurred at soil temperatures from 12 °C (at 15 °C/5 °C) to 43 °C (at 35 °C/25 °C) with optimum temperatures of 27-30 °C, similar to other CAM succulents and consistent with the distribution of this shallow-rooted species in warm regions. Although a doubled CO2 concentration did not alter the optimum or limiting soil temperatures, increases of up to 5 °C in these temperatures accompanied the 20 °C increase in day/night air temperatures. 3. Root elongation rates at optimum soil temperatures ranged from 5.4 mm day-1 (15 °C/5 °C), through 6.6 mm day-1 (25 °C/15 °C), to 10.4 mm day-1 (35 °C/25 °C) with a 25% increase under a doubled CO2 concentration. Highest root elongation rates at 35 °C/25 °C may reflect changing root vs shoot sink strengths in a species with a highly plastic root system. 4. At limiting soil temperatures, the length of the cell division zone was reduced by an average of 20% and cell length at the mid-point of the elongation zone by 10%. Increased root elongation rates under a doubled CO2 concentration reflected increased cell elongation. 5. The temperature response for the roots of O. ficus-indica and stimulation of elongation by a doubled CO2 concentration indicate that root growth for this highly productive species should be enhanced by predicted global climate change

Responses of CAM species to increasing atmospheric CO\u3csub\u3e2\u3c/sub\u3e concentrations

Crassulacean acid metabolism (CAM) species show an average increase in biomass productivity of 35% in response to a doubled atmospheric CO2 concentration. Daily net CO2 uptake is similarly enhanced, reflecting in part an increase in chlorenchyma thickness and accompanied by an even greater increase in water-use efficiency. The responses of net CO2 uptake in CAM species to increasing atmospheric CO2 concentrations are similar to those for C3 species and much greater than those for C4 species. Increases in net daily CO2 uptake by CAM plants under elevated atmospheric CO2 concentrations reflect increases in both Rubisco-mediated daytime CO2 uptake and phosphoenolpyruvate carboxylase (PEPCase)-mediated night-time CO2 uptake, the latter resulting in increased nocturnal malate accumulation. Chlorophyll contents and the activities of Rubisco and PEPCase decrease under elevated atmospheric CO2, but the activated percentage for Rubisco increases and the K(M)(HCO3-) for PEPCase decreases, resulting in more efficient photosynthesis. Increases in root:shoot ratios and the formation of additional photosynthetic organs, together with increases in sucrose-Pi synthase and starch synthase activity in these organs under elevated atmospheric CO2 concentrations, decrease the potential feedback inhibition of photosynthesis. Longer-term studies for several CAM species show no downward acclimatization of photosynthesis in response to elevated atmospheric CO2 concentrations. With increasing temperature and drought duration, the percentage enhancement of daily net CO2 uptake caused by elevated atmospheric CO2 concentrations increases. Thus net CO2 uptake, productivity, and the potential area for cultivation of CAM species will be enhanced by the increasing atmospheric CO2 concentrations and the increasing temperatures associated with global climate change

Development, fabrication and test of a high purity silica heat shield

A highly reflective hyperpure ( 25 ppm ion impurities) slip cast fused silica heat shield material developed for planetary entry probes was successfully scaled up. Process development activities for slip casting large parts included green strength improvements, casting slip preparation, aggregate casting, strength, reflectance, and subscale fabrication. Successful fabrication of a one-half scale Saturn probe (shape and size) heat shield was accomplished while maintaining the silica high purity and reflectance through the scale-up process. However, stress analysis of this original aggregate slip cast material indicated a small margin of safety (MS. = +4%) using a factor of safety of 1.25. An alternate hyperpure material formulation to increase the strength and toughness for a greater safety margin was evaluated. The alternate material incorporates short hyperpure silica fibers into the casting slip. The best formulation evaluated has a 50% by weight fiber addition resulting in an 80% increase in flexural strength and a 170% increase in toughness over the original aggregate slip cast materials with comparable reflectance

South London Community Education Provider Networks : evaluation report

Community Education Provider Networks (CEPNs) are innovative network organisations designed to support workforce transformation, through education and training, for a primary and community orientated National Health Service . In developing CEPNs, Health Education England (HEE) has been a pathfinder for innovation in primary care workforce development across a diverse health care system which covers a population of approximately three and quarter million people. This final evaluation report, following on from the interim report of 2015, offers a system wide assessment. It also identifies key issues and learning points for the development of such education and training network organisations