Nitrogen dynamics in the Westerschelde estuary (SW Netherlands) estimated by means of the ecosystem model MOSES

A tentative nitrogen budget for the Westerschelde (SW Netherlands) is constructed by means of a simulation model with thirteen spatial compartments. Biochemical and chemical processes in the water column are dynamically modeled; fluxes of dissolved constituents across the water-bottom interface are expressed by means of diagenetic equations.The model is calibrated on a large amount of observed variables in the estuary (1980–1986) with relatively fine temporal and spatial detail. Additional constraints are imposed by the stoichiometric coupling of carbon, nitrogen and oxygen flows and the required conservation of mass. The model is able to reproduce rather well the observed distributions of nitrate, ammonium, oxygen and Kjeldahl nitrogen both in time and space. Also, model output of biochemical oxygen demand and total organic carbon falls within observed ranges.By far the most pervasive process in the nitrogen cycle of the estuary is nitrification which mainly takes place in the water column of the upper estuarine part. On average about three times as much nitrate is leaving the estuary at the sea side compared to what enters from the river and from waste discharges. Ammonium on the other hand is consumed much faster (nitrification) than it is regenerated and only about one third of the total import leaves the estuary at the sea side. The budget for detrital nitrogen reveals import from the river, from wastes and from the sea. Phytoplankton uptake of inorganic nitrogen is negligible in the model.About 21% of total nitrogen, 33% of inorganic nitrogen, is removed from the estuary (mainly to the atmosphere through denitrification) and the load of nitrogen net exported to the sea amounts to about 51 000 tonnes per year. Total denitrification in our model is lower than what was estimated in the literature from the late seventies, where a nitrogen removal up to 40–50% of the total inorganic load was reported. Part of the differences could be methodological, but inspection of the nutrient profiles that led to these conclusions show them to be different to the ones used in our study. The oxygen deficient zone has moved upstream since the late seventies, entrailing the zone of denitrification into the riverine part of the Schelde. The nitrification process now starts immediately upon entering the estuary.     

Bis[dihydrobis(1-pyrazolyl)borate]cadmium(II): a monomeric, severely distorted tetrahedral complex of cadmium(II)

The crystal structure of the complex [H₂B(pz)₂]₂Cd has been determined: orthorhombic, Pbca, A = 16.052(3), B = 13.935(3), C = 14.974(4) Å, V = 3349.4(13) ų, Z = 8, R(F) = 3.61%. It is the first structurally characterized non-porphyrin CdN₄ complex. It is monomeric in the solid state with a pseudotetrahedral geometry about the cadmium atom. The N---Cd---N angles are distorted by the approximate 93° bite angle of the ligand; the interligand N---Cd---N angles also are distorted, ranging from 106.9 to 131.7°. These distortions are the result of intermolecular packing forces and are facilitated by the spherical set of valence orbitals for Cd²⁺.     

DNA uptake by imbibition and expression of a foreign gene in rice

Uptake of DNA by imbibition of dry and viable rice ( Oryza sativa L.) embryos from a DNA solution and expression of a foreign gene were detected using two different vectors contaíning gusA (β-glucuronidase) and hpt (hygromycin phosphotransferase) as reporter genes. The frequency of transient expression of gusA and hpt genes using the CaMV35S promoter was about 30 to 50%. The main sites of gusA gene expression were meristems of roots and vascular bundles of leaves. Also, DNA uptake, integration and expression of the hpt gene in selected rice were investigated by various PCR methods and Southern blot analysis of genomic DNA. It was shown that the hygromycin phosphotransferase (HPT) DNA was present in the rice genome in an integrated form and not as a plasmid form.     

细枝木麻黄气生瘤的人工形成

细枝木麻黄气生瘤的人工形成邹铧,张忠泽,张成刚,丁鉴,王育英,付莉（中国科学院沈阳应用生态研究所,沈阳１１００１５）ＡｒｔｉｆｉｃｉａｌｆｏｒｍａｔｉｏｎｏｆａｅｒｉａｌｎｏｄｕｌｅｓｏｎＣａｓｕａｒｉｎａｃｕｎｎｉｎｇｈａｍｉａｎａ￥ＺｏｕＨｕａ;...     

N,P供给对作物排放N2O的影响研究初报

Ｎ、Ｐ供给对作物排放Ｎ_２Ｏ的影响研究初报陈欣,沈善敏,张璐,吴杰,王学强（中国科学院沈阳应用生态研究所,沈阳１１００１５）ＡｐｒｅｌｉｍｉｎａｒｙｒｅｓｅａｒｃｈｏｎｔｈｅｅｆｆｅｃｔｏｆｎｉｔｒｏｇｅｎａｎｄｐｈｏｓｐｈｏｒｕｓｓｕｐｐｌｙｏｎＮ_...     

鸡粪中氨基酸含量测定与开发利用

本文对蛋鸡饲料与鸡粪进行了１３次１６种氨基酸含量的测定分析,氨基酸含量稳定,鸡粪中氨基酸含量比常用的部分饲料中氨基酸含量高。鸡对饲料中蛋白质的利用率仅为２９％;大部分蛋白质仍在鸡粪中,从分析结果看,１００克鸡粪中含有各种氨基酸１０．４５克。鸡粪取材广泛,价格低廉,氨基酸便于提取,有广阔的开发利用前景。     

Patterns of diversity in the strata of boreal montane forest in British Columbia

Abstract. Patterns of diversity were analyzed in a boreal coniferous forest and its strata (tree, shrub, herb and bryophyte layers): number of species per community — α-diversity, total species richness — γ-diversity, mean similarity — β-diversity, and mosaic diversity, a measure of complexity. These four measures of diversity consistently decreased from lower to upper vegetation layers. To study the effect of juveniles of larger life forms on diversity of lower layers, they were removed from the data and the measures of diversity reanalyzed. Number of species per community and mosaic diversity decreased substantially, but β-diversity did not change. So, the effect of juveniles on γ-diversity is due to the greater number of species per community. Multiple regression models revealed that the relationships between α-diversity and the environmental variables were the same for the whole forest and for the herb layer. Elevation and soil pH were the major variables explaining α-diversity in the whole community. Climate was the only environmental gradient related to species richness in all individual strata. Tree and herb richness values were negatively related to soil drainage and acidity, respectively. Species richness of the plant community was affected by environmental variability mostly through the herb layer. Various explanations of the observed diversity patterns included: environmental constraints, resource competition, generation time, and colonization processes.     

Carbon and nitrogen mineralization from decomposing gypsy moth frass

Defoliation of forests by insects is often assumed to produce a pulse of available nitrogen (N) from the decomposition of frass pellets. In this study we measured rates of carbon (C) and N mineralization from gypsy moth frass incubated with and without soil, and for soil alone. Incubations were at constant temperature and soil moisture conditions and lasted for 120 days. We found that gypsy moth frass contains much labile C as well as extractable N, and that the stimulation of microbial growth by the labile C results in immobilization of essentially all of the extractable N in the frass. The response of the microbes is fast, beginning within 1 day and lasting at least 90 days. This immobilization response represents an efficient mechanism for conserving N within a forest ecosystem after a defoliation event.     

Patterns of light and nitrogen distribution in relation to whole canopy carbon gain in C3 and C4 mono- and dicotyledonous species

An analytical model was used to describe the optimal nitrogen distribution. From this model, it was hypothesized that the non-uniformity of the nitrogen distribution increases with the canopy extinction rate for light and the total amount of free nitrogen in the canopy, and that it is independent of the slope of the relation between light saturated photosynthesis (P_m) and leaf nitrogen content (n_L). These hypotheses were tested experimentally for plants with inherently different architectures and different photosynthetic modes. A garden experiment was carried out with a C₃ monocot [rice, Oryza sativa (L.)], a C₃ dicot [soybean, Glycine max (L.) Merr] a C₄ monocot [sorghum, Sorghum bicolor (L.) Moensch] and a C₄ dicot [amarantus, Amaranthus cruentus (L.)]. Leaf photosynthetic characteristics as well as light and nitrogen distribution in the canopies of dense stands of these species were measured. The dicot stands were found to have higher extinction coefficients for light than the monocot stands. Dicots also had more non-uniform N distribution patterns. The main difference between the C₃ and C₄ species was that the C₄ species were found to have a greater slope value of the leaf-level P_m—n_L relation. Patterns of N distribution were similar in stands of the C₃ and C₄ species. In general, these experimental results were in accordance with the model predictions, in that the pattern of nitrogen allocation in the canopy is mainly determined by the extinction coefficient for light and the total amount of free nitrogen.     

Variation in the natural abundance of 15N in the halophyte,Salicornia virginica,associated with groundwater subsidies of nitrogen in a southern California salt-marsh

To provide insight into the importance of the salt-marsh ecotone as a sink for inorganic nitrogen in perched groundwater, measurements were made of the natural abundance of ¹⁵N in dissolved NO₃-N and NH₄-N and in the salt-marsh halophyte, Salicornia virginica, along an environmental gradient from agricultural land into a salt-marsh. The increase in the natural abundance of ¹⁵N (expressed by convention as ¹⁵N) of NO₃-N, accompanied by the decrease in NO₃-N (and total dissolved inorganic N, DIN) concentration along the gradient, suggested that the salt-marsh ecotone is a site of transformation, most likely through denitrification, of inorganic nitrogen in groundwater. ¹⁵N enrichment in S. virginica (and the parasitic herb, Cuscuta salina), along the tidal marsh boundary, relative to high and middle marsh locations, indicated the retention of groundwater nitrogen as vegetative biomass. The correlation between ¹⁵N _Salicornia and ¹⁵N_NH4 suggested a preference for NH₄-N over NO₃-N during uptake by this plant. Groundwater inputs enhanced the standing crop, above-ground productivity, and nitrogen content of S. virginica but the ralative effects of pore water salinity and DIN concentration on these parameters were not determined. ¹⁵N enrichment of marsh plants by groundwater DIN inputs could prove useful in tracing the fate of these inputs in the marsh food web.