CHANGES IN CELL CHEMICAL COMPOSITION DURING THE LIFE CYCLE OF SCRIPPSIELLA TROCHOIDEA (DINOPHYCEAE)1

The cellular content of carbon, nitrogen, amino acids, polysaccharides, phosphorus and adenosine trtphosphate (ATP) was determined at several stages during the life cycle of the dinoflagellate Scrippsiella trochoidea (Stein) Loeblich. Carbon per cell decreased slightly between exponential and stationary phase growth in vegetative cells whereas nitrogen per cell did not change. Both of these cellular components increased markedly on encystment and then decreased to vegetative cell levels during dormancy and germination. C/N ratios increased gradually during cyst dormancy and activation, reflecting a more rapid decrease in N than in C pools, even though both decreased through time. Amino acid composition was relatively constant during the vegetative cell stages; glutamic acid was the dominant component. Arginine was notably higher in cysts than in vegetative cells but decreased significantly during germination, suggesting a role in nitrogen storage. The ratio of neutral ammo acids to total ammo acids (NAA/TAA) decreased as cysts were formed and then gradually increased during storage and germination. The ratio of basic ammo acids to total ammo acids (BAA/TAA) changed in the opposite direction of NAA/TAA, whereas the ratio of acidic acids to total amino adds (AAA/TAA) was generally invariant. Ammo acid pools were not static during the resting slate in the cysts: there was degradation or biosynthesis of certain, but not all, classes of these compounds. The monosacchande composition of cold and hot water extracted polysaccharides was quite different between cells and cysts. A high percentage of glucose in cysts suggests that the storage carbohydrate is probably in the form of glucan. Total cellular phosphorus was higher in all cyst stages than in vegetative cells. However, ATP-cell^?1 decreased as vegetative cells entered stationary phase and encysted, and continued to decrease in cysts during dark cold storage. ATP increased only as the cysts were activated at warm temperatures in the light and began to germinate. The above data demonstrate that dormancy and quiescence are not periods of inactive metabolism but instead are times when numerous biochemical transformations are occurring that permit prolonged survival in a resting state.     

INFLUENCE OF CELL SHAPE AND SIZE ON ALGAL COMPETITIVE ABILITY1

Allometric relations between physiological processes and cell volume and surface area are combined with the variable-internal-stores model of growth to predict the ability of hypothetical phytoplankton to compete for phosphorus at equilibrium. The analysis shows that for spherical cells, smaller cells are better competitors than large ones. For cells that are very elongated in shape, however, large cells are often better competitors than small ones. The cells predicted to be the best competitors compare favorably in size and shape with the species observed to dominate in phosphorus-limited chemostats at equilibrium.     

Stoichiometric relations in an ant-treehopper mutualism

Carbon : nitrogen : phosphorus (C : N : P) stoichiometry can underlie physiological and life history characteristics that shape ecological interactions. Despite its potential importance, there is much to learn about the causes and consequences of stoichiometric variation in terrestrial consumers. Here we show that treehoppers (Publilia modesta) tended by ants (Formica obscuripes) contained lower N concentrations than treehoppers on plants from which ants were excluded. Ant presence also affected nutrient concentrations in host plants: on plants with ants, leaves contained uniformly low concentrations of N; on plants without ants, N concentrations were low only in the few leaves fed upon by treehoppers at the time of collection. We suggest treehopper feeding reduces leaf nutrient levels and ants positively affect treehopper abundance, producing a top–down effect on plant quality. Determining the causes of these stoichiometric changes should help elucidate factors guiding the dynamics of conditional mutualisms between ants and homopterans.     

土壤水分和氮磷营养对冬小麦根系生长及水分利用的调节

模拟试验研究结果表明：在土壤相对含水量为４０％￣７０％范围内,水分亏缺严重,根水势和蒸腾蒸发量显著降低,根系生长严重受阻,根长变短,根干重降低,随着土壤水分趋于良好,根水势和蒸腾蒸发量显著增加,根干重在土壤相对含水量为５５％￣６２％之间时最大,而土壤相对含水量在５５％上下时根长达最长;土壤水分趋于轻度干旱有利根系下扎,土壤水分趋于良好利于根量增长。氮磷营养对小麦根系生长具有明显的调节作用。磷营养可     

农业生态系统中磷循环的研究进展

1　引　言能量转化和物质循环是农业生态系统最基本的功能特征。1976年在荷兰召开的第一次农业生态系统矿质养分循环研讨会标志着从系统层次研究物流的开始,但物流仍是系统研究的薄弱环节,特别是较高系统层次准确的物流的数量概念更为缺乏[1,2]。生态系统中营养元素的输入、输出状况反映了一个地区生产发展水平的高低和生态系统功能的强弱;而投入、产出的动态变化,则显示了一定时期内营养元素循环的基本规律[3]。在各种水平(如地球、陆地、国家或生态系统)上的有关磷循环的论文也发表了不少,借以阐述各组成部分中磷的数量及其相互间的转化速…     

Induction of Blocks in Nuclear Divisions and Overcondensation of Meiotic Chromosomes with Cycloheximide During Conjugation of Tetrahymena thermophila

During conjugation, the micronucleus of Tetrahymena thermophila undergoes five consecutive nuclear divisions: meiosis, third prezygotic division (pregamic mitosis) and two postzygotic mitoses of the synkaryon. The four products of the synkaryon differentiate into macronuclear anlagen and new micronuclei and the old macronucleus is resorbed. The protein synthesis inhibitor cycloheximide, applied during conjugation, induced several developmental blocks. Pairs shifted to the drug during early meiotic prophase (stages I–III) were arrested at prophase. Cycloheximide applied to cells at pachytene (stages IV-VI) to metaphase arrested the conjugants at the stage of modified prometaphase/metaphase with overcondensed, swollen bivalents. In contrast to other systems, in the presence of cycloheximide, separation of chromatids, decondensation of chromosomes and exit from metaphase I were inhibited in both diploid and haploid cells. Pairs shifted to the drug after metaphase I were arrested at postmeiotic interphase after completing one nuclear cycle. The same rule applied to the subsequent cycle; then cells were arrested at the stage of pronuclei, and those pairs with functional pronuclei and synkarya were arrested at the stage of two products of the first postzygotic division (pronuclei were not arrested in nuclear transfer and karyogamy). Only pairs with two products of the first postzygotic division were arrested at the same stage after the cycloheximide treatment. Pairs shifted to cycloheximide during the second postzygotic division were arrested in development of macronuclear anlagen and resorption of old macronuclei. The postmeiotic conjugants pulse-treated with cycloheximide (2 h) yielded heterokaryons retaining parental macronuclei (i.e. they exhibited macronuclear retention).     

An attempt to predict long-term effects of atmospheric nitrogen deposition on the yield of Norway spruce stands (Picea abies (L.) Karst.) in southwestern Sweden

Long-term field experiments in Norway spruce stands on fertile sites (site indices 27–35 m) in southwestern Sweden were analysed with respect to volume increment. Three treatments were included (0=No fertilization, N = Fertilization with N, NP = Fertilization with N and P).Volume growth was monitored for 18 years in 10 blocks. No significant differences in annual volume increment between the treatments were detected. Volume increments in the N treatment were 97%, 99% and 107% as high as those in the 0 treatment for the periods 1–5, 6–10 and 11–15 years after the first fertilization. Corresponding values for the NP treatment were 104%, 108% and 110%, indicating that P has a small positive effect.The amount of N-fertilization would correspond to an annual N deposition of 20 kg ha^-1 during the next 30 years in southwestern Sweden. For this period, the results imply that this N deposition would not affect the growth of Norway spruce stands on fertile sites.     

Growth and nutrient dynamics of beech (Fagus sylvatica L.) seedlings in acid soils

The relative uptake rates of N, P, K, S, Ca, Mg, Fe, Mn, Zn, Cu, and Al were estimated in beech seedlings pot cultured in the field in six acid soils (treatments). The relative uptake rates were compared with the relative growth rates. The relative uptake rates of N, K and Ca agreed well with the growth rates of the seedlings irrespective of widely differing soil conditions (acid sand-clayey till, pH 4–6). The relative uptake rates of P, Fe, and Al differed from that predicted by the growth rate. The uptake rates of Fe and Al were highest at the lowest growth rates, and the P uptake rate was lower than the growth rate in these treatments. Thus the P availability probably limited growth in an eluvial (E) horizon of a podzol, and possibly in the illuvial (B) horizon of a podzol and in an acid clayey till (Dystric Cambisol). Low P uptake was associated with a tendency towards higher relative root growth rates. In terms of the concept of steady state nutrition the high relative root growth rate in some treatments may be interpreted as an acclimation to low P supply. The P limitation seemed to be related to interactions among Fe, Al and organic compounds of the soil solution.FAX no: +4646104423     

Plant nutrition and growth: Basic principles

Soil compaction may restrict shoot growth of sugar beet plants. Roots, however, are the plant organs directly exposed to soil compaction and should therefore be primarily affected. The aim of this study was to determine the influence of mechanical resistance and aeration of compacted soil on root and shoot growth and on phosphorus supply of sugar beet. For this purpose, a silt loam soil was adjusted to bulk densities of 1.30, 1.50 and 1.65 g cm^–3 and water tensions of 300 and 60 hPa. Sugar beet was grown in a growth chamber under constant climatic conditions for 4 weeks. Both, decrease of water tension and increase of bulk density impeded root and shoot growth. In contrast, the P supply of the plants was differently affected. At the same air-filled pore volume, the P concentration of the shoots was reduced by a decrease of soil water tension, but not by an increase of bulk density. Both factors also reduced root length and root hair formation, however, in compacted soil the plants partly substituted for the reduction of root size by increasing the P uptake efficiency per unit of root. Shoot growth decreased when root growth was restricted. Both characteristics were closely related irrespective of the cause of root growth limitation by either compaction or water saturation. It is therefore concluded that shoot growth in both the compacted and the wet soil was regulated by root growth. The main factor impeding root growth in compacted soil was penetration resistance, not soil aeration.FAX no corresponding author: +49551 5056299     

Influence of rhizodeposition under elevated CO2 on plant nutrition and soil organic matter

Atmospheric CO₂ concentrations can influence ecosystem carbon storage through net primary production (NPP), soil carbon storage, or both. In assessing the potential for carbon storage in terrestrial ecosystems under elevated CO₂, both NPP and processing of soil organic matter (SOM), as well as the multiple links between them, must be examined. Within this context, both the quantity and quality of carbon flux from roots to soil are important, since roots produce specialized compounds that enhance nutrient acquisition (affecting NPP), and since the flux of organic compounds from roots to soil fuels soil microbial activity (affecting processing of SOM).From the perspective of root physiology, a technique is described which uses genetically engineered bacteria to detect the distribution and amount of flux of particular compounds from single roots to non-sterile soils. Other experiments from several labs are noted which explore effects of elevated CO₂ on root acid phosphatase, phosphomonoesterase, and citrate production, all associated with phosphorus nutrition. From a soil perspective, effects of elevated CO₂ on the processing of SOM developed under a C4 grassland but planted with C3 California grassland species were examined under low (unamended) and high (amended with 20 g m^–2 NPK) nutrients; measurements of soil atmosphere 13C combined with soil respiration rates show that during vegetative growth in February, elevated CO₂ decreased respiration of carbon from C4 SOM in high nutrient soils but not in unamended soils.This emphasis on the impacts of carbon loss from roots on both NPP and SOM processing will be essential to understanding terrestrial ecosystem carbon storage under changing atmospheric CO₂ concentrations.Abbreviations SOM soil organic matter - NPP net primary productivity - NEP net ecosystem productivity - PNPP p-nitrophenyl phosphate