Decomposition and transfer of plant residue 14C between size and density fractions in soil

The aim of our study was to follow the transfer of ¹⁴C-labeled ryegrass between size and density fractions of soil organic matter in a sandy and a loam soil. Our hypotheses were a) that the applied ¹⁴C would be transferred from light and soluble fractions to intermediate and heavy macroorganic matter fractions (>150 m) and finally become stabilized in microaggregates (<150 m), and b) that the physical protection of ¹⁴C associated with microaggregates against decomposition would decrease with increasing saturation of the microaggregates with soil organic matter. Generally, the hypotheses were confirmed. Immediately after application most of the label was present in the soluble and light macroorganic matter fractions. Newly synthesized microbial biomass fed on the labeled components of the fractions. The amounts of ¹⁴C in the soluble and light macroorganic matter fractions decreased rapidly, while the amounts of ¹⁴C in the intermediate and heavy macroorganic matter fractions and in microaggregates remained more or less stable. At the end of the incubation most of the residual soil ¹⁴C was found in the microaggregates. In the sandy soil ¹⁴C was concentrated in the 20–150 m fraction, whereas in the loam a larger proportion was present in the <20 m fraction.The mineralization rates of ¹⁴C-labeled material were similar in the light intermediate and heavy fractions of macroorganic matter and in the microaggregates 0 and 180 days after the application of ¹⁴C-labeled ryegrass. In all fractions, ¹⁴C mineralized more rapidly than total C. The results indicate that considerable amounts of ¹⁴C must have transferred from the soluble and light macroorganic matter fractions and newly synthesized microbial biomass to the intermediate and heavy macroorganic matter fractions and the microaggregates, and that ¹⁴C was not yet physically protected against microbial degradation during the whole incubation period. The degree of physical protection of ¹⁴C against decomposition in the microaggregate fraction <20 m was negatively correlated with the degree of saturation of this particle size fraction with soil organic matter.     

Regulation of nitrate assimilation in the cyanobacterium Phormidium laminosum

The intracellular ratio of 2-oxoglutarate to glutamine has been analyzed under nutritional conditions leading to different activity levels of nitrate-assimilating enzymes in Phormidium laminosum (Agardh) Gom. This non-N₂-fixing cyanobacterium adapted to the available nitrogen source by modifying its nitrate reductase (NR; EC 1.7.7.2), nitrite reductase (NiR; EC 1.7.7.1) and glutamine synthetase (GS; EC 6.3.1.2) activities. The 2-oxoglutarate/glutamine ratio was similar in cells adapted to grow with nitrate or ammonium. However, metabolic conditions that increased this ratio [i.e., nitrogen starvation or l-methionine-d,l-sulfoximine (MSX) treatment] corresponded to high activity levels of NR, NiR, GS (except in MSX-treated cells) and glutamate synthase (GOGAT; EC 1.4.7.1). By contrast, metabolic conditions that diminished this ratio (i.e., addition of ammonium to nitrate-growing cells or addition of nitrate or ammonium to nitrogen-starved cells) resulted in low activity levels. The variation in the 2-oxoglutarate/glutamine ratio preceded the changes in enzyme activities. These results suggest that changes in the 2-oxoglutarate/glutamine ratio could be the signal that triggers the adaptation of P. laminosum cells to variations in the available nitrogen source, as occurs in enterobacteria.Abbreviations Chl chlorophyll - GOGAT ferredoxin-dependent glutamate synthase (EC 1.4.7.1) - GS glutamine synthetase (EC 6.3.1.2) - MSX l-methionine-d,l-sulfoximine - NiR nitrite reductase (EC 1.7.7.1) - NR nitrate reductase (EC 1.7.7.2) - TP total protein This work has been partially supported by grants from the Spanish Ministry of Education and Science (DGICYT PB88-0300 and PB92-0464) and the University of the Basque Country (042.310-EC203/94). M.I.T. was the recipient of a fellowship from the Basque Government.     

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⁺.     

Effects of aluminium on growth and root reactions of phosphorus stressed Betula pendula seedlings

The impact of two constant non-toxic levels of Al stress (0.2 and 0.4 mM) on growth and ³²P uptake capacity on sub-optimal (P-limited) Betula pendula seedlings grown in sand culture was examined.Seedling growth was under optimum controlled conditions in a growth chamber where nutrient additions were made at a predetermined relative addition rate (R_A) of 10% day^-1. Three treatment groups of seedlings 0, 0.2 and 0.4 mM Al were harvested at 15, 29 and 42 days. The excised roots were exposed to a ³²P-labelled solution for 15 minutes to measure their capacity for P uptake. Growth was determined by weighing the roots, stems and leaves of the seedlings.Growth data showed that relative growth rate (R_G) should equal the R_A of P the most limiting nutrient, which was supplied at P/N 3% instead of an optimal 15%. Therefore, Ingestad's theory can also be used succesfully in sand culture and this may be particularly important for future studies of root and rhizosphere exudates. Low levels of Al (< 0.2 mM) in combination with low P supply significantly lowered the R_G of the birch seedlings by further reducing P supply. However, previous studies of birch seedling growth and nutrient uptake using Ingestad's solution culture technique with optimumal P supply did not show any effect of Al on growth untill the Al was in excess of 3 mM. Aluminium was not directly toxic to the plants and therefore roots could respond to the ³²P bioassay.     

Effects of irrigation and balanced fertilization on nutrient cycling in a Douglas fir stand

The effects on growth and nutrient status of an increased availability of all major nutrients was studied in a 40 year old Douglas fir stand. The nutrient amounts were applied by daily sprinkling and were in fixed, optimal proportions to the estimated annual uptake of N. Irrigation was included to avoid drought stress. The nutrient applications were also done in combination with a lower NH₄ load, realized under a roof that was placed above the ground. According to nutritional standards nitrogen supply was optimal and was related to the moderately high atmospheric N inputs. Nutrition of P, K and in some years Ca seemed critical.In all four studied growing seasons water additions resulted in a growth increase, of 30 to 40%. Irrigation decreased needle fall. Nutrient applications increased the needle concentrations of P and K considerably, but this did not result in a growth enhancement. Fertilization also increased K and P in shedded needles. Only minor leaching losses were calculated. The recovery in trees of fertilizer K and P was maximally 15%. Input-output budgets suggested that P was strongly retained in the soil. The decrease in NH₄ load had slightly decreased N availability and soil acidification, and seemed to enhance tree growth. The use of tree growth as a parameter to evaluate the effects of an improved nutritional balance is discussed.     

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。     

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.