Responses of nitrogen and phosphorus resorption from leaves and branches to long-term nitrogen deposition in a Chinese fir plantation

为了解森林养分内循环对全球变化的响应, 基于长期模拟氮沉降试验, 研究了杉木(Cunninghamia lanceolata)人工林不同龄级(一年生、二年生和衰老)叶和枝的氮(N)、磷(P)养分分配及其再吸收特征, 并分析了不同模拟N沉降处理时间(7年和14年)杉木叶N、P养分再吸收差异。在12年生杉木中开展模拟N沉降试验, 以尿素(CO(NH₂)₂)为N源, 设N0、N1、N2和N3 4个处理水平, 施氮量分别为0、60、120和240 kg·hm ^-2·a ^-1, 每个处理重复3次。结果表明: (1)叶和枝在衰老过程中碳(C)、N和P含量逐渐降低, 且叶的C、N和P含量比枝高; N含量大小依次为一年生叶>二年生叶>衰老叶>一年生枝>二年生枝>衰老枝, 且N3 > N2 > N1 > N0, 而C:N则呈现相反的趋势; 衰老器官的C:N、C:P、N:P比新鲜器官高; N沉降增加了不同龄级叶和枝(除二年生叶外)的N、N:P和C:P, 但降低了P和C:N。(2)叶和枝的N、P养分再吸收率(RE_N、RE_P)随龄级的增加至衰老有规律地递减, 且RE_P > RE_N; 受长期N沉降的影响, RE_N叶(28.12%) <枝(30.00%), 而RE_P则为叶(45.82%) >枝(30.42%); 杉木叶和枝N:P与RE_N:RE_P之间存在极显著的线性相关关系。(3)随N沉降处理时间的增加, 叶RE_N呈降低态势, 各处理(N1、N2和N3)分别降低了9.85%、3.17%和11.71%; 而RE_P则明显上升, 分别增加了71.98%、42.25%和9.60%。研究结果表明: 不同器官、不同龄级的养分再吸收率随氮沉降处理的水平、处理时间而所有不同; RE_N:RE_P与N:P之间存在紧密关系。     

Effects of variations in soil water potential,depth of N placement,and cultivar on postanthesis N uptake by wheat

This study was conducted to investigate the influence of soil water potential, depth of N placement, timing, and cultivar on uptake of a small dose of labeled N applied after anthesis by wheat (Triticum aestivum L.) Understanding postanthesis N accumulation should allow better control of grain protein concentration through proper manipulation of inputs. Two hard, red spring-wheat cultivars were planted in early and late fall each yr of a 2-yr field experiment. Less than 1 kg N ha^–1 as K ¹⁵NO₃ was injected into the soil at two depths: shallow (0.05 to 0.08 m) and deep (0.15 to 0.18 m). In both years an irrigation was applied at anthesis, and injections of labeled N were timed 4, 12, and 20 days after anthesis (DAA). Soil water potential was estimated at the time of injection. Mean recovery of ¹⁵N in grain and straw was 57% of the ¹⁵N applied. Recovery did not differ between the high-protein (Yecora Rojo) and the low-protein (Anza or Yolo) cultivars. Mean recovery from deep placement was 60% versus only 54% from shallow placement (p < 0.01). Delaying the time of injection decreased mean recovery significantly from 58% at 4 DAA to 54% at 20 DAA. This decrease was most pronounced in the shallow placement, where soil drying was most severe. Regressions of recovery on soil water potential of individual cultivar x yr x planting x depth treatments were significant only under the driest conditions. Stepwise regression of ¹⁵N recovery on soil water potential and yield parameters using data from all treatments of both years resulted in an equation including soil water potential and N yield, with a multiple correlation coefficient of 0.64. The translocation of ¹⁵N to grain was higher (0.89) than the nitrogen harvest index (0.69), and showed a highly significant increase with increase in DAA. This experiment indicates that the N uptake capacity of wheat remains reasonably constant between 4 and 20 DAA unless soil drying is severe.     

Somatic polyploidy in extraembryonic membranes of the snake,Elaphe guttata

Summary Video-densitometric DNA measurements of Feulgenstained tissues of 42 day old eggs of the corn snake,Elaphe g. guttata (Columbridae, Serpentes), revealed a basic DNA content of 2C=2.17 pg, with somatic polyploidy in the allantois, the chorioallontois, the yolk sac, and other extraembryonic membranes. The maximum value determined was 128C (in binucleate cells 2×128C) at the distal pole of the egg. This is the first report of somatic polyploidy in a snake, and one of the first in reptiles in general.     

The effect of CuSO4 for establishing in vitro culture,and the role nitrogen and iron sources in in vitro multiplication of Corylus avellana L. cv. Tonda Gentile Romana

Abstract

In the present work, we have used copper sulphate (CuSO₄·5H₂O) enriched medium for effective control of visible and latent contamination. Among the different concentrations used, 1.25–2.5?mg/L resulted the most appropriate. In addition, the role of different nitrogen source and concentrations (NH₄NO₃ and KNO₃), as different iron source (FeEDTA and FeEDDHA) has been investigated in the proliferation and rooting phases of European hazelnut (cv. Tonda Gentile Romana). The normal concentration of nitrogen present in Murashige and Skoog medium is too high for hazelnut micropropagation cv. Tonda Gentile Romana. A reduction of total nitrogen, accompanied by a reduction of ammonium forms, resulted in a better quality of the shoots. Similar results have been obtained when the common iron source FeEDTA has been replaced by the same concentration of FeEDDHA. An increase in rooting occurs when the amount of nitrogen was reduced in the rooting medium, particularly when the NH₄NO₃ was not present.     

Biochemical composition of the parasitic amphipod Hyperia galba in relation to age and starvation

Summary Hyperia galba was collected in the waters around Helgoland and in the Weser-Elbe-estuary during autumn. Its mode of life is a temporary but obligatory parasitism. The basal biochemical composition of the adults was analyzed in detail and related to the fresh, dry, and ash-free dry weight as well as sex and body length. Hyperia galba (males/females) consists of 85/86% water; the dry matter contains approximately 64/61% protein, 10/11% lipid, 1.2/1.5% carbohydrate, 10/8% chitin, and 23/23% ash. The analyses of basal elemental composition yielded approximately 38% C, 9% N and 6% H. Under natural conditions, individuals may encounter at least two periods of food shortage during their lives. Therefore, the analyses were carried out on individuals of different developmental stages also under food deprivation. The data are discussed with respect to the special mode of life of the species and compared with those found by other authors in several related crustacean species.Abbreviations AFDW ash-free dry weight - BL body length - DW dry weight - SD standard deviation - WW wet weight     

Effect of Different Carbon and Nitrogen Sources on Clostridium argentinense Toxigenicity in Coculture withPseudomonas mendocina

The effect of different carbon and nitrogen sources on the production of toxin by Clostridium argentinense was examined. The toxin production by C. argentinense in coculture with Pseudomonas mendocina increased in all the cases in relation to that produced by monocultures independent of the nature of the source. Using dextrin as carbon source C. argentinense produced the highest levels of toxin both in monocultures (300 LD₅₀/mL) and in cocultures with P. mendocina (5000 LD₅₀/mL). Experiments run in a microfermenter showed that the slow growth of cocultures associated with the assimilation of dextrin and the pH and Eh profiles favoured the production of toxin. Of the nitrogen sources assayed, corn steep liquor sustained the highest levels of toxin in both monocultures and cocultures with 3 and 2.8 fold increases with respect to that obtained using proteose peptone. The toxin production by C. argentinense cultures and C. argentinense–P. mendocina cocultures was highly dependent on the nature of the carbon and nitrogen sources used in the culture media. Growth of C. argentinense on substrates slowly assimilated stimulated the production of toxin.     

Litter quality in a north European transect versus carbon storage potential

Newly shed foliar plant litter often has a decomposition rate of ca 0.1–0.2% day^–1, which decreases greatly with time and may reach 0.0001 to 0.00001% day^–1 or lower in litter material in the last stages of decay. The decrease in decomposability (substrate quality) varies among species and is complex, involving both direct chemical changes in the substrate itself and the succession in microorganisms able to compete for substrate with a given chemical composition. In late stages, the decomposition appears very little affected by climate, suggesting that climate change will have little effect on late-stages decomposition rates. Here, we apply a model for the late stages of litter decomposition to address the question of climate-change effects on soil-C storage. Decomposition of litter turning into soil organic matter (SOM) is determined by the degradation rate of lignin. In the last phases of decay, raised N concentrations have a rate-retarding effect on lignin degradation and thus on the decomposition of far-decomposed litter and litter in near-humus stages. The retardation of the decomposition rate in late stages may be so strong that decomposition reaches a limit value at which total mass losses virtually stop. At such a stage the remaining litter would be close to that of stabilized SOM. The estimated limit values for different species range from about 45 to 100% decomposition indicating that between 0 and 55% should either be stabilized or decompose extremely slowly. For no less than 106 long-term studies on litter decomposition, encompassing 21 litter types, limit values were significantly and negatively related to N concentration, meaning that the higher the N concentration in the newly shed litter (the lower the C/N ratio) the more litter was left when it reached its limit value. Trees growing under warmer and wetter climates (higher actual evapotranspiration, AET) tend to shed foliar litter more rich in N than those growing under colder and drier climates. A change in climate resulting in higher AET would thus mean that within species, e.g., Scots pine, a higher N level in the foliar litter may result. Further, within the boreal system deciduous species appear to have foliar litter richer in N than have conifers and within the conifers group, Norway spruce has needle litter more rich in N than, e.g., Scots pine. Thus, a change of species (e.g., by planting) from pine to spruce or from spruce to a deciduous species such as birch may result in a higher N level in the litter fall at a given site. In both cases the result would be a lower limit value for decomposition. The paper presents an hypothesis, largely based on available data that a change in climate of 4° higher annual average temperature and 40% higher precipitation in the Baltic basin would result in higher N levels in litter, lower decomposition and thus a considerable increase in humus accumulation.