Search

A soil resampling approach has detected an early stage of recovery in the cation chemistry of spruce forest soil due to reductions in acid deposition. That approach is limited by the lack of soil data and archived soil samples prior to major increases in acid deposition during the latter half of the 20th century. An alternative approach is the dendrochemical analysis of dated wood to detect temporal changes in base cations back into the 19th century. To infer environmental change from dendrochemical patterns of essential base cations, internal factors that affect cation chemistry such as the maturation of sapwood and the spread of wood infection need to be recognized. Potassium concentration was a useful marker of these internal maturation and infection that could affect the concentration of essential base cations in wood. Dendrochemical patterns in samples of red spruce in the eastern United States and Norway spruce in northwestern Russia were used to determine how internal changes in base cations can be separated from external changes in root-zone soil to date major changes in the availability of essential base cations associated with a changing environment.

Whole-tree harvest (WTH) may compromise tree productivity and health and lead to soil and surface water acidification. The aim of this study was to assess the long-term change (up to circa 40 years) in soil exchangeable calcium (Ca 2+ ) pools following conventional (CH) and WTH at three Swedish coniferous sites. A second aim was to evaluate how well the results could be reproduced by the dynamic model MAGIC (Model of Acidification of Groundwater in Catchments). Soil Ca 2+ pools (down to 20 cm) decreased at all three sites from stand age 15–16 to 37–38 years. The depletion ranged from 2.6 to 8.6 kEq ha −1 (26.5–52.7%) and 0.2 to 5.0 kEq ha −1 (2.3–49.1%) in the CH and WTH treatment, respectively. The presence of an interaction effect indicated that the main effect of time was not statistically significant at all three sites. Over the course of time, soil Ca 2+ pools have also become more similar between the CH and WTH treatments, but the Ca 2+ pools were still significantly lower ( p 2+ pools were generally greater than what has been found in other studies and were largely explained by high soil Ca 2+ availability and high tree Ca 2+ uptake, especially in the CH-plots, as indicated by the MAGIC mass balance budgets. Model simulations by MAGIC partly agreed with the measured data. However, the model exaggerated the soil Ca 2+ losses between 1990 and 2013 (CH = 3.6–9.9 kEq ha −1 ; WTH = 3.0–8.3 kEq ha −1 ), especially at the spruce sites. Furthermore, MAGIC could not reproduce the rapid diminishing differences between CH and WTH. Uncertainties in model parameters, underestimated soil Ca 2+ pools or biological feed-back mechanisms could explain this discrepancy. Until these have been resolved, interpretations of Ca 2+ changes related to CH or WTH using dynamic modelling or mass balance budget calculations should be done with caution.

Photosystem II (PS II) evolves oxygen from two bound water molecules in a four-stepped reaction that is driven by four quanta of light, each oxidizing the chlorophyll moiety P680 to yield P+680. When starting from its dark equilibrium (mainly state S1), the catalytic center can be clocked through its redox states (S0ellipsisS4) by a series of short flashes of light. The center involves at least a Mn4-cluster and a special tyrosine residue, named YZ, as redox cofactors plus two essential ionic cofactors, Cl- and Ca2+. Centers which have lost Ca2+ do not evolve oxygen. We investigated the stepped progression in dark-adapted PS II core particles after the removal of Ca2+. YZ was oxidized from the first flash on. The difference spectrum of YZ-->YoxZ differed from the one in competent centers, where it has been ascribed to a hydrogen-bonded tyrosinate. The rate of the electron transfer from YZ to P+680 was slowed down by three orders of magnitude and its kinetic isotope effect rose up from 1.1 to 2.5. Proton release into the bulk was now a prerequisite for the electron transfer from YZ to P+680. On the basis of these results and similar effects in Mn-(plus Ca2+-)depleted PS II (M. Haumann et al., Biochemistry, 38 (1999) 1258-1267) we conclude that the presence of Ca2+ in the catalytic center is required to tune the apparent pK of a base cluster, B, to which YZ is linked by hydrogen bonds. The deposition of a proton on B within close proximity of YZ (not its release into the bulk!) is a necessary condition for the reduction in nanoseconds of P+680 and for the functioning of water oxidation. The removal of Ca2+ rises the pK of B, thereby disturbing the hydrogen bonded structure of YZB.

Male Lewis rats (n = 27) were fed a nonpurified diet containing 0.9% calcium, 0.7% phosphorus, and 0.005% zinc until 8 wk of age. At this time rats were assigned randomly to one of two groups. Both groups were fed a low calcium, low zinc, purified diet (0.2% calcium, 0.4% phosphorus, less than 0.00007% zinc), but one group was fed 1.78 mg Zn/(animal.d). The zinc-replete animals were individually matched by weight to the zinc-depleted animals and pari-fed. Balances and plasma concentrations of zinc, calcium, and phosphorus and parathyroid hormone, 25 hydroxycholecalciferol [25(OH)D] and 1,25-dihydroxycholecalciferol [1,25(OH)2D] were determined at the start of calcium depletion and 2 wk later. Calcium and 25(OH)D levels were lower in both groups after calcium depletion. Dietary zinc had no significant effect on calcium or 25(OH)D levels. Phosphorus concentrations were lower after calcium depletion, but phosphorus concentration was higher in the zinc-depleted compared with the zinc-replete group at the end of the experiment. 1,25(OH)2D increased in both groups, but was higher in the zinc-replete than the zinc-depleted group at the end of the experiment. Calcium and phosphorus balances were greater in the zinc-depleted group at the end of the experiment. We conclude zinc depletion diminishes the response of 1,25(OH)2D to calcium depletion in rats. The mechanism is unknown, but may involve nonhormonally mediated changes in gastrointestinal absorption of calcium and phosphorus or an affect of zinc on extraintestinal processes.

In smooth muscle of guinea pig taenia coli, showing spontaneous activity, the curves of rhythmic changes in muscle tension appears parallel to the curves of changes in Po2 level in the medium (1-3). On the other hand, Saito et al. (3) reported that an application of high K (isotonically, 40 mM) caused an increase in oxygen consumption accompanying increase in tension change in taenia coli, and that this was in accordance with the concept (4, 5) that the K-induced tonic response resulted from a transmembrane transport of Ca that depended on the aerobic breakdown of carbohydrates. In the present paper, effects of Ca depletion on the oxygen consumption accompanying muscle tension change both spontaneous and that induced by high K were studied, and a dissociation of the changes in oxygen consumption and muscle tension change was attempted by substituting strontium (Sr) for Ca in the external medium. Some of the results have already been reported (6, 7).

THE retention of radiocalcium or radiostrontium in bones of humans (Spencer et al., 1961), rats (Cohn et al., 1961) and non-laying pullets (Hurwitz, 1965a), following a single intravenous dose, is reduced by the feeding of high-calcium diets. However, in the laying hen, the severe calcium depletion from bone during calcium restriction (Taylor and Moore, 1954; Hurwitz and Griminger, 1961) would suggest the possibility of reducing the body burden of bone-seeking radiosotopes by calcium restriction. It was the purpose of the present study to investigate the effects of variation in dietary calcium level and sources, and the timing of this variation, on the retention of calcium-45 and strontium-85 in various bone segments, and the deposition of these nuclides in the egg shell. METHODS AND RESULTS General procedure: The method for preparation of samples for analysis was given in detail in the preceding paper (Hurwitz and Bar, 1966). For calcium-45 determinations, calcium …

Calcium in rats' teeth was labeled with radioactive Ca-45 by feeding the animals a calcium-free diet and administering calcium as calcium-45 levulinate biweekly for eight weeks starting with a two weeks' old animal. The radioactive teeth were removed and the calcium deletion which resulted from immersion of the teeth in various liquids for twenty-Pour hours was determined by tracer methods. The liquids tested were distilled water, commercial mouthwashes, citric and tartaric acid solutions, beverages, milk, and human saliva.