Recent advances in photoelectric aerosol measurements

After recalling briefly the optical properties of aerosols, we describe the principle and the working conditions of photoelectric apparatus for aerosol measurements. Two size distribution analyzers are presented: the first one is based on a classical detection principle, the minimum detectable radius being 0.2 µm, and the maximum concentration 3 × 10⁴ particles cm^?3; the second one is based on a photon counting technique, with which particles of radius between 0.03 and 0.2 µm can be measured at maximum number concentration of 2 × 10⁶ particles cm^?3. We describe then two Condensation Nuclei Counters (CNC) with continuous flux; in these types of apparatus, the vapor of a liquid is condensed on Aitken nuclei using a Peltier effect device. They are thereby rendered visible and counted using a classical photoelectric method. One apparatus works under normal conditions of pressure and temperature, while the other one works under stratospheric conditions, i.e., at low pressure and temperature. The concentration range is still between 10 and 10⁶ nuclei cm^?3 and the minimum concentration is 0.1 particle cm^?3 in the case of the stratospheric counter. The four devices work on individual particles; their characteristics are compared to those of commercially available apparatus and their advantages discussed.     

Photosynthetic responses and N allocation in Douglas-fir needles following a brief pulse of nutrients

The temporal distribution of soil nutrients is heterogeneous, and thus the uptake, storage and later remobilization of brief nutrient pulses may be critical for growth in nutrient-limited habitats. We investigated the response of photosynthesis and the major nitrogen (N) fractions in needles of 2-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings to a 15-day nutrient pulse (containing 250 ppm N). The nutrient pulse (N pulse) was imposed in late July, toward the end of the seedlings' third growing season, and subsequent changes in photosynthesis and needle N fractions were examined over the following 3 months. Needles are sites of photosynthesis and putative storage organs. Thus we tested two hypotheses: (1) N from the N pulse is quickly synthesized from soluble non-protein N into soluble proteins, especially Rubisco, and (2) the N pulse increases photosynthetic rates and thus growth. We also examined an alternative hypothesis that Rubisco functions also as a storage protein, in which case we would predict increases in amount of Rubisco in response to the N pulse without concomitant increases in photosynthesis. Soluble non-protein N was the most dynamic N pool and may have constituted a temporary storage reservoir; however, the quantitative significance of soluble non-protein N is questionable because this pool was at most only 7% of total N. Concentrations of Rubisco were unaffected by the N-pulse treatment and there was little evidence that Rubisco served as a storage protein. Nutrient-pulse seedlings added twice as much dry mass as controls during the 3 months post-treatment (Warren et al. 2003a). Over the same period, the maximum rate of light-saturated photosynthesis (A(max)) declined to low rates in control seedlings, whereas A(max) increased in N-pulse seedlings. Nevertheless, treatment and temporal trends in N and Rubisco content per unit area were poorly related to A(max), and it seems likely that photosynthesis was limited by additional factors, perhaps thylakoid proteins or an inadequate supply of other nutrients.     

Optimizing metamorphosis in <Emphasis Type="Italic">Paracentrotus lividus</Emphasis> aquaculture using alternative macroalgae species to <Emphasis Type="Italic">Corallina</Emphasis> sp.

Metamorphosis induction cues (by chemical mediation or direct contact) were tested in Paracentrotus lividus using three different macroalgae treatments: Corallina sp., Palmaria palmata, and Laminaria digitata. Higher percentages of metamorphosis were reached in Paracentrotus lividus larvae by direct contact with a Palmaria palmata substrate.