This study compared the traditional two-compartment (fat mass or FM; fat free mass or FFM) hydrodensitometric method of body composition measurement, which is based on body density, with three (FM, total body water or TBW, fat free dry mass)- and four (FM, TBW, bone mineral mass or BMM, residual)-compartment models in highly trained men (n = 12), sedentary men (n = 12), highly trained women (n = 12), and sedentary women (n = 12). The means and variances for the relative body fat (%BF) differences between the two- and three-compartment models [2.2 +/- 1.6 (SD) % BF; n = 48] were significantly greater (P = 0.02) than those between the three- and four-compartment models (0.2 +/- 0.3% BF; n = 48) for all four groups. The three-compartment model is more valid than the two-compartment hydrodensitometric model because it controls for biological variability in TBW, but additional control for interindividual variability in BMM via the four-compartment model achieves little extra accuracy. The combined group (n = 48) exhibited greater (P < 0.001) FFM densities (1.1075 +/- 0.0049 g/cm3) than the hydrodensitometric assumption of 1.1000 g/cm3, which is based on analyses of three male cadavers aged 25, 35, and 46 yr. This was primarily because their FFM hydration (72.4 +/- 1.1%; n = 48) was lower (P = 0.001) than the hydrodensitometric assumption of 73.72%.
Hypotheses to explain the source of the 1011 tons of
salt in groundwaters of the Murray Basin, south-eastern Australia, are
evaluated; these are (a) mixing with original sea water,
(b) dissolution of salt deposits,
(c) weathering of aquifer minerals and
(d) acquisition of solutes via rainfall. The total
salinity and chemistry of many groundwater samples are similar to sea-water
composition. However, their stable isotopic compositions
(δ18O= –6.5 ‰;
δ2H = –35) are typical of mean winter
rainfall, indicating that all the original sea water has been flushed out of
the aquifer. Br/Cl mass ratios are approximately the same as sea water
(3.57 x 10-3) indicating that NaCl evaporites (which
have Br/Cl<10-4) are not a significant
contributor to Cl in the groundwater. Similarly, very low abundances of Cl in
aquifer minerals preclude rock weathering as a significant source of Cl. About
1.5 million tons of new salt is deposited in the Murray–Darling Basin
each year by rainfall.The groundwater chemistry has evolved by a combination
of atmospheric fallout of marine and continentally derived solutes and removal
of water by evapo-transpiration over tens of thousands of years of relative
aridity. Carbonate dissolution/precipitation, cation exchange and
reconstitution of secondary clay minerals in the aquifers results in a
groundwater chemistry that retains a ‘sea-water-like’ character.
The natural abundance hydrogen-isotope composition of leaf water ([Formula: see text]) and leaf organic matter (δ D (org) ) was measured in leaves of C3 and C4 dicotyledons and monocotyledons. The [Formula: see text] value of leaf water showed a marked diurnal variation, greatest enrichment being observed about midday. However, this variation was greater in the more slowly transpiring C4 plants than in C3 plants under comparable environmental conditions. A model based on analogies with a constant feed pan of evaporating water was developed and the difference between C3 and C4 plants expressed in terms of either differences in kinetic enrichment or different leaf morphology. Microclimatic and morphological features of the leaves which may be associated with this factor are discussed. There was no daily excursion in the δ D (org) value in leaves of either C3 or C4 plants. When δ D (org) values were referenced to the mean [Formula: see text] values during the period of active photosynthesis, the discrimination against deuterium during photosynthetic metabolism (ΔD) was greater in C3 plants (-117 to -121‰) than in C4 plants (-86 to -109‰).These results show that the different water use "strategies" of C3 and C4 plants are responsible for the measured difference in deuterium-isotope composition of leaf water. However, it is unlikely that these physical processes account fully for the differences in hydrogen-isotope composition of the products of C3 and C4 photosynthetic metabolism.
Abstract. The authors examine the isotopic composition of leaf water, at natural abundance levels, as influenced by transpiration rate. The isotopic composition of water of wheat leaves (Triticum aestivum L. var. Aroona) was followed while their transpiration rate adjusted to ‘steady‐state’ environmental conditions. Leaf diffusive resistance was modified by short‐term salt treatment and by plant culture in either nutrient solution, free‐draining sand, or vermiculite. Resultant changes in 18O and 2H in leaf water are described and fitted to the model of Leaney et al. (1985). The treatments with lower transpiration rates were found to have a greater fraction of their leaf water equilibrated with water vapour in the atmosphere. Comparable results were obtained with both 18O and 2H, with some differences being interpreted in terms of turbulence in the vapour diffusion path. The fraction of the leaf water equilibrated with the atmosphere varied between leaves of different ages. However, this may have been due to their different positions in the canopy.
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