Metal distribution across different pools in the organic layer of a forest under acid deposition and its consequences for the metal dynamics

Acid atmospheric deposition can cause losses of metal nutrients from the organic layer of a soil. The size of these losses depend on the sizes of the different pools in which the metals are present, as these pools differ in mobility. The metal pools in an organic soil layer of a Douglas fir forest in the Netherlands subjected to acid deposition were determined by means of extractions and percolations. Na was mainly dissolved and exchangeably adsorbed, K dissolved, exchangeably adsorbed and present in the soil microbial biomass, Ca exchangeably adsorbed and present in organic precipitates, Mg exchangeably adsorbed and present in the soil biomass, and Mn exchangeably adsorbed and present in inorganic precipitates. The main part of the metals was exchangeably adsorbed. The adsorption affinity increased in the order Na < K < Mg < Mn ≈ Ca. The vertical distribution of the metals in the organic layer showed that all metals were continuously lost from the organic layer. The differences between the metals in retention and vertical distribution patterns were in agreement with their differences in deposition rate, pool distribution, and exchange affinity. Since the metals were mainly exchangeably adsorbed, and the acidifying cations dominated the atmospheric deposition, acid deposition and cation exchange must be processes that strongly affect the losses of metals from this organic soil layer. R F Huettl Section editor     

Towards an understanding of the relations between tree nutrition,nutrient cycling and environment

The paper contains a discussion of the interrelations between the sciences used by managers of forest land to improve their management, in particular with respect to the plant nutrient economy of the forest ecosystems. Both site studies and studies of nutrient cycling have been carried out for long periods without proper consideration of tree nutrition. Therefore these studies contributed less to the understanding of the role of nutrients as regulators of processes in ecosystems than might have been expected. This situation has improved, especially within the last decade. In addition the necessity to manage forest land for environmental values as well as for forest yield requires new interdisciplinary approaches in the study of the roles of plant nutrients in the forest. Even more branches of biological and environmental sciences than those just mentioned must be involved.     

Phosphorus limitation of forest leaf area and net primary production on a highly weathered soil

We tested the hypothesis that P was the nutrient limiting net primary production of a nativeMetrosideros polymorpha forest on a highly weathered montane tropical soil in Hawaii. A factorial experiment used all combinations of three fertilizer treatments: nitrogen (N), phosphorus (P) and a mix of other essential nutrients (OE), consisting primarily of mineral derived cations and excluding N and P. P addition, but not N or OE, increased leaf area index within 12 months, foliar P concentration measured at 18 months, and stem diameter increment within 18 months. Stem growth at 18 months was even greater when trees fertilized with P also received the OE treatment. N and P additions increased leaf litterfall and N and P in combination further increased litterfall. The sequence of responses suggests that increased available P promoted an increase in photosynthetic area which led to increased wood production. P was the essential element most limiting to primary production on old volcanic soil in contrast to the N limitation found on young volcanic soils.     

Application of a fry (0+;) abundance index, based on semi-quantitative electrofishing, to predict Atlantic salmon smolt runs in the River Bush, Northern Ireland

An abundance index for 0+ Atlantic salmon was based on semi-quantitative electrofishing estimates at 137 sites in typical juvenile habitat throughout the River Bush (N. Ireland). 0 + abundance was linearly related to total smolt numbers migrating through a downstream trap in subsequent years ( r ²= 0.716, P <0.001), suggesting a high degree of predictive ability. This predictive ability decreased as smolt age increased, suggesting influence of density-independent mortality. Potential application of the technique to estimate smolt production from rivers having no trapping facilities is discussed, together with sources of variability potentially affecting estimates.     

Zooplankton as a compound mineralising and synthesizing system: phosphorus excretion

Data on phosphate excretion rates of zooplankton are based on measurements using the pelagic crustacean zooplankton of Lake Vechten and laboratory-cultured Daphnia galeata. In case of Daphnia sp we measured the effects of feeding on P-rich algae and P-poor algae (Scenedesmus) as food on the P-excretion rates at 20°C. The excretion rates of the natural zooplankton community, irrespective of the influence of the factors mentioned, varied by an order of magnitude: 0.025–0.275µg PO₄-Pmg^–1C in zooplankton (C _zp ) h^–1. The temperature accounted for about half the observed variation in excretion rates. The mean excretion rates in the lake, computed for 20°C, varied between 0.141 and 0.260 µg Pmg^–1C _zp h^–1. Based on data of zooplankton biomass in the lake the P-regeneration rates by zooplankton covered between 22 and 239% of the P-demand of phytoplankton during the different months of the study period.In D. galeata, whereas the C/P ratios of the Scenedesmus used as food differed by a factor 5 in the experiments, the excretion rates differed by factor 3 only. Despite the higher P-excretion rates (0.258± 0.022 µg PO₄-P mg^–1 C h^–1) of the daphnids fed with P-rich food than those fed with P-poor food (0.105 ± 0.047 µg PO₄-P mg^–1 C h^p–1), both the categories of the animals were apparently conserving P. A survey of the literature on zooplankton excretion shows that in Daphnia the excretion rates vary by a factor 30, irrespective of the species and size of animals and method of estimation and temperature used.About two-thirds of this variation can be explained by size and temperature. A major problem of comparability of studies on P-regeneration by zooplankton relates to the existing techniques of P determination, which necessitates concentrating the animals several times above the in situ concentration (crowding) and prolonged experimental duration (starving), both of which manifest in marked changes that probably lead to underestimation of the real rates.     

Mitochondrial DNA sequence variation and genetic stock structure of Atlantic cod (Gadus morhua) from bay and offshore locations on the Newfoundland continental shelf

Bay cod, Atlantic cod (Gadus morhua) that over-winter in the deep-water bays of northeastern Newfoundland, have historically been regarded as distinct in migration and spawning behaviour from offshore (Grand Bank) cod stocks. To investigate their genetic relationships, we determined the DNA sequence of a 307-base-pair portion of the mitochondrial cytochrome b gene for 236 adult cod taken from the waters off northeastern Newfoundland, including fish found over-wintering and spawning in Trinity Bay. Although 17 genotypes were found, a single common genotype occurs at a frequency of greater than 80% in all samples, and no alternative genotype occurs at a frequency of greater than 3%. Genotype proportions did not differ significantly among samples. Measures of genetic subdivision among sampling locations are nil. Cod over-wintering in Trinity Bay are not genetically distinct from offshore cod. In combination with tagging and physiological studies, these data suggest that there is sufficient movement of cod between bay and offshore locations to prevent the development or maintenance of independent inshore stocks. Adult cod that over-winter in Trinity Bay appear to represent an assemblage of temporarily nonmigratory fish that have become physiologically acclimated to cold-water inshore environments. The pattern of genetic variation in northern cod suggests a recent population structure characterized by extensive movement of contemporary individuals superimposed on an older structure characterized by a bottleneck in the population size of cod in the north-western Atlantic.     

Effect of Acetate on Esterase C Activity During the Growth Cycle of Paramecium*

SYNOPSIS Enhanced esterase C activity could be demonstrated by starch gel electrophoresis in various stocks of Paramecium spp. (P. primaurelia stocks 90 and 540, P. biaurelia stock 93, P. tetraurelia stock 29. P. pentaurelia stock 87, P. octaurelia stocks 31 and 300, and P. multimicronucleatum species 3, stock 8 MO) grown in Adaptation Medium. This esterase, however, was barely detectable when they were cultivated in Axenic Medium. Addition of trypticase to Adaptation Medium resulted in reduction of esterase C in the ciliates. This effect is ascribable to Na acetate present in trypticase. Since esterase C increased with the decrease in acetate concentration (as estimated by gas-liquid chromatography) during growth of Paramecium, acetate appears to be utilized by the cells. Sensitivity of esterase C to acetate occurs in all 6 species of Paramecium examined. Different stocks within a species may have different levels of sensitivity; in one case this is genetically determined. The results emphasize the importance of controlling and manipulating growth conditions for the assessment of inter- and intraspecies variations in the isozymes of Paramecium.     

Mild phosphorus stress in barley and a related low-phosphorus-adapted barleygrass: Phosphorus fractions and phosphate absorption in relation to growth

Barleygrass ( Hordeum leporinum ) from Australian low-P (phosphorus) soils and commercial barley ( H. vulgare ) with high fertilizer requirements were grown in solution culture at 3 levels of P supply. The high-P-adapted barley produced more biomass at all levels of P supply and was more responsive to added P in terms of rate of tillering, rate of leaf production, final leaf size, and therefore total shoot weight compared to barleygrass. In both species root: shoot ratio decreased in response to improved tissue P status, even at P levels where total biomass did not respond to P supply. Removal of endosperm reserves of barley reduced total biomass to a greater extent than it altered phosphate absorption rate, thus increasing tissue P status and making plants less responsive to added P. Similarly, barleygrass had a slower growth rate but a comparable P absorption rate to that of barley. Thus barleygrass also accumulated tissue P and was unresponsive to added P. All phosphorus chemical fractions increased in response to improved tissue P status, but to differing extents (inorganic-P > nucleic acid-P > lipid-P > ester-P), suggesting that all P fractions (particularly inorganic P) serve, in part, a storage function. Both barleygrass and barley without endosperm had higher concentrations of all P fractions (particularly inorganic P) than did unaltered barley, but this was due entirely to their higher P status (due to slow growth) rather than to any major difference in P metabolism between species. We conclude that slow growth is more important than interspecific differences in P metabolism, P absorption, or efficiency of P utilization in explaining the success of barleygrass and other low-P-adapted species on infertile soils.     

NITRATE UPTAKE BY LAMINARIA LONGICRURIS (PHAEOPHYCEAE)1,2

Laminaria longicrucis De la Pylaie took up exogenous nitrate under both summer and winter conditions. During July and August no NO₃^- was detected in the ambient water or in algal tissues although it was present in both in February. Discs (2.3 cm diam.) of thin blade tissue were incubated with NO₃^- at four temperatures, with and without illumination. Similar values Jor NO₃^- uptake were found for both summer and winter collected plants when measured in light at 0 C. An apparent K of 4–6 μM was recorded for both types of plants; the V_max ranged from 7 to 10 μmol h^-1 g^-1 dry wt measured in ca. 1800 μW cm^-2 of cool-white fluorescent light. Uptake rates at 5 C were 66%, and at 0 C 30% of those for controls run at 15 C. The alga scavenged NO₃- from solutions <0.5 μM. Ammonia did not inhibit NO₃- uptake. Antibiotic pretreatment reduced NO₃- uptake by a maximum of 12%. Nitrite uptake was inhibited in proportion to the concentration of NO₃- in the medium.