Wood cellulose preparation methods and mass spectrometric analyses of delta13C, delta18O, and nonexchangeable delta2H values in cellulose, sugar, and starch: an interlaboratory comparison.

Interlaboratory comparisons involving nine European stable isotope laboratories have shown that the routine methods of cellulose preparation resulted in data that generally agreed within the precision of the isotope ratio mass spectrometry (IRMS) method used: +/-0.2 per thousand for carbon and +/-0.3 per thousand for oxygen. For carbon, the results suggest that holocellulose is enriched up to 0.39 per thousand in 13C relative to the purified alpha-cellulose. The comparisons of IRMS measurements of carbon on cellulose, sugars, and starches showed low deviations from -0.23 to +0.23 per thousand between laboratories. For oxygen, IRMS measurements varied between means from -0.39 to 0.58 per thousand, -0.89 to 0.42 per thousand, and -1.30 to 1.16 per thousand for celluloses, sugars, and starches, respectively. This can be explained by different effects arising from the use of low- or high-temperature pyrolysis and by the variation between laboratories in the procedures used for drying and storage of samples. The results of analyses of nonexchangeable hydrogen are very similar in means with standard deviations between individual methods from +/-2.7 to +/-4.9 per thousand. The use of a one-point calibration (IAEA-CH7) gave significant positive offsets in delta2H values up to 6 per thousand. Detailed analysis of the results allows us to make the following recommendations in order to increase quality and compatibility of the common data bank: (1) removal of a pretreatment with organic solvents, (2) a purification step with 17% sodium hydroxide solution during cellulose preparation procedure, (3) measurements of oxygen isotopes under an argon hood, (4) use of calibration standard materials, which are of similar nature to that of the measured samples, and (5) using a two-point calibration method for reliable result calculation.

Light and salinity affect growth of the salt marsh plant Aster laurentianus.

• The effects are reported of substrate salinity and light on the relative growth rate of the annual Aster laurentianus, an endangered species of eastern Canadian salt marshes. • The independent and combined effects of photosynthetically active photon flux density and salinity on the relative growth rate (RGR) and overall plant performance were measured in glasshouse and growth-chamber experiments on seedlings of A. laurentianus. • Low light availability decreased RGR through its negative effect on unit leaf rate. However, specific leaf area and leaf mass ratio varied inversely with changes in light, such that leaf area ratio did not differ greatly among light levels. High salinity decreased RGR by reducing unit leaf rate and leaf area ratio; a reduction in the latter was brought about by a lower leaf mass ratio rather than by a lower specific leaf area. Low light availability combined with high substrate salinity affected A. laurentianus in a strictly additive manner; there was no significant interaction between the two factors on overall plant performance. • Light and salinity are important factors controlling growth of A. laurentianus, and might explain the distribution pattern of the species in the field.