防治月季蜘蛛螨的探索

月季在国际切花市场的销售量一直位居第一,并且是欧洲及世界其他地区公园和庭院的主要观赏植物。但是,蜘蛛螨(二点叶螨)严重影响了陆地和温室栽培月季的质量。这是因为蜘蛛螨能够越冬繁殖且生长发育速度快,并且能快速对大多数广谱杀螨剂产生抗性。人们一直在寻求防治蜘蛛螨的最     

Nitrogen mineralization in a pecan (Carya illinoensis K. Koch)–cotton (Gossypium hirsutum L.) alley cropping system in the southern United States

Information on temporal and spatial patterns of N mineralization is critical in designing tree-crop mixed systems that could maximize N uptake while minimizing N loss. We quantified N mineralization rates in a pecan (Carya illinoensis K. Koch)–cotton (Gossypium hirsutum L.) alley cropping system in northwestern Florida with (non-barrier) and without tree-crop belowground interactions (barrier separating the root systems of pecan and cotton). Monthly rates of mineralization were estimated using buried bag incubations over a 15-month period. In addition, seasonal mineralization rates and cotton lint yield on soils supplied with two sources of N—inorganic fertilizer and organic poultry litter—were assessed. Results indicated that temporal variations in net NH₄ and NO₃ accumulation and mineralization rates were driven primarily by environmental factors and to a lesser degree by initial soil NH₄ and NO₃ levels. Mineralization varied by belowground interaction treatment during the initial growing season, when the non-barrier treatment exhibited a higher mineralization rate than the barrier treatment, likely due to reduced nutrient uptake by cotton in the non-barrier or a higher degree of immobilization in the barrier treatment. Mineralization during the second growing season was similar for both treatments. Source of N had no effects on N transformation in the soil. Lint yield reductions were observed in the non-barrier treatment during both years compared to the barrier treatment, likely due to interspecific competition for water. Yield differences between treatments in the second growing season were likely compounded by a diminishing pre-study fallow effect. Source of N was found to have a significant effect on cotton yield, with inorganic fertilizer resulting in 39% higher lint compared to poultry litter in the barrier treatment.     

The effect of sample storage on the extraction of Cu,Zn, Fe,Mn and organic material from oxidized estuarine sediments

Concentrations of extractable Cu, Zn, Fe and Mn in oxidized estuarine sediment are influenced by the manner and time of storage between collection and extraction. No storage method tested completely preserves the initial chemical and physical characteristics of the sediment. Freezing or (for some extractions) drying are adequate methods of storage if sediments are to be extracted only with acids. However, if a variety of extractants is to be used, extractions should be conducted as soon as practical after collection.     

Influence of aroma compounds on the mechanical properties of pectin gels

A detailed study of the rheological behavior of pectin gels, in the presence of aroma compounds in food concentration is reported. In high methoxylated pectin (HMP) gels, it has not yet been shown if aroma compounds can be responsible for modifications in rheology. Two rheological techniques were used to measure the impact of aroma substances on rheological properties of HMP-based systems. Maximum strain to fracture (sigma F) was compared between flavored and unflavored gels on stress-displacement curve, which was obtained with uniaxial compression until fracture. An oscillatory rheometer was applied to determine the gelation time (Tgel). It appeared that all the aroma compounds studied increased significantly sigma F. It is generally acknowledged that hydrophobic interactions are the main interactions leading to HMP gelation, and the more hydrophobic interactions there are, the higher the sigma F. It is assumed that esters might increase sigma F through the increase of hydrophobic interactions in HMP network. For solvents (ethanol, propylene glycol), a cosolute effect could explain the increase in firmness for HMP-based gels.     

Differences in the chemical composition of dissolved organic matter from waste material of different sources

The chemical composition of waste-material-derived dissolved organic matter (DOM) was characterized by chemolytic analyses and ¹H, ¹³C and ³¹P nuclear magnetic resonance (NMR) spectroscopy. Dissolved organic matter was extracted by water from an aerobic fermented urban waste compost, a sewage sludge and a pig slurry and then fractionated using the XAD-8 method. The amount of water-extractable dissolved organic carbon (DOC) ranged from 3% in the sewage sludge to 22% in the pig slurry. Dissolved organic matter isolated from pig slurry was equally distributed between hydrophilic and hydrophobic DOC, whereas in the sewage-sludge-derived material the hydrophobic fraction was predominant. Dissolved organic C from the urban waste compost was mainly within the hydrophilic fraction. Wet-chemical analysis and ¹H- and ¹³C-NMR spectra showed that both DOM fractions from the urban waste compost were low in neutral, acidic and amino sugars as well as in lignin-derived compounds. In turn, the materials were rich in low-molecular-weight aliphatic compounds. The chemical structure of both fractions is probably the result of the intensive transformation of urban waste compost during its fermentation. The hydrophilic fractions of DOM from sewage sludge and pig slurry contained considerable amounts of carbohydrates but were also rich in low-molecular-weight aliphatics. The respective hydrophobic fractions had the largest contents of CuO-extractable phenols which may in part derive from sources other than lignin. By contrast with the other materials, the hydrophobic fraction from the pig slurry seemed to contain polymeric rather than low-molecular-weight material. The ³¹P-NMR spectrum of the hydrophilic DOM fraction from urban waste compost did not show signals of inorganic or organic P compounds while the spectrum of the hydrophobic fraction revealed traces of monoester P, diester P, and orthophosphate. ³¹P-NMR spectroscopy suggested that both the hydrophobic and hydrophilic fractions from pig slurry did not contain organic P. The hydrophilic DOM fraction from sewage sludge contained orthophosphate, organic monoester P and a little pyrophosphate. The hydrophobic fraction contained mainly organic diester P and smaller amounts of teichoic acids and organic monoester P. Considering that water-soluble fractions of urban waste compost contained no easily plant-available P and a low content of labile organics, we conclude that this material contains less labile nutrients and is more refractory than the soluble constituents of pig slurry and sewage sludge.     

Dissolved organic phosphorus and sulphur as influenced by sorptive interactions with mineral subsoil horizons

This study tested the hypothesis that, like dissolved organic nitrogen (N), dissolved organic phosphorus (P) and sulphur (S) are more mobile in soil than is organic carbon (C). To do so, I compared the sorption of organic P and S to subsoil materials with that of organic C. Soil samples were equilibrated with water‐soluble organic matter from the forest floor at pH 4 and in the equilibrium solutions organic C, P, and S, and their distributions between the hydrophilic and hydrophobic fraction were determined. Sorption of C within the organic matter did not differ from that of P and S. However, the hydrophilic fraction contained the vast majority of P and S and sorbed far less than the hydrophobic fraction. So the overall retention of organic P and S was smaller than that of organic C. This result suggested that dissolved organic matter is more important in the loss of plant nutrients than in the release of C from soil.     

What predicts nitrous oxide emissions and denitrification N-loss from European soils?

N₂0 emissions and denitrification N-losses. precipitation, air temperature, soil moisture, bulk density and content of mineral N were monitored in 9 different agricultural soils in 6 European countries throughout the vegetation period (April to September) 1992 and 1993. N₂O emissions and denitrification N-losses were log-normal distributed, reflecting high temporal changes. While small flux rates (< 2 g N ha^?1 d^?1) were detectable every day, high rates (> 10 g N ha^?1 d^?1) were measured after fertilization. An attempt to relate the emission variables to climate and soil variables was made through the use of correlation analysis. The mean N₂0 emissions from soil were significantly correlated with the soil properties clay, organic C and mineral N content and the amount of applied mineral N fertilizer. The best prediction of the N₂O emission rates (r² = 0.734) was achieved by multiple linear regression using the soil parameter clay and mineral N. Only 50% of the observed variation could be explained by the factors C_org and mineral N, which describe the substrate availability for microbial processes. No successful statistical model was found for the prediction of denitrification N-losses.     

Genetic diversity of winter wheat in Shaanxi province, China, and other common wheat germplasm pools

Cultivated Chinese wheat germplasm has been a valuable genetic resourcein international plant breeding. Landraces endemic to China are a geneticresource that is distinct from other wheat germplasm. Patterns of geneticdiversity among cultivated Chinese accessions and relationship to othergermplasm pools are unknown, despite the proven value and potential novelty. Theobjective of this work was to determine the level of genetic diversity withinimproved Chinese germplasm in the context of several other wheat germplasmpools. We analyzed a set of improved accessions cultivated from the 1940s to the1990s in Shaanxi province, China, using six simple sequence repeat (SSR) primerpairs and 30 restriction fragment length polymorphism - probe enzymecombinations (RFLP-PEC) previously used to characterize 21 geographically basedgermplasm pools. Shaanxi germplasm consists of three groups based on foreignintroductions from Italy, Australia, Denmark, and Russia. There was a decreasein genetic diversity among Shaanxi accessions cultivated in the 1970s and 1980sto the 1990s, and accession classifications based on primary decade ofcultivation were found to be significantly undifferentiated. The analysis of themean genetic distance among 22 geographically based pools of germplasm suggestsseveral regions are significantly undifferentiated. A vast majority of the totalamount of variation was found within pools; therefore, pools appear to belargely differentiated based on small differences in band relative frequency andfew if any unique bands. Previous studies have identified some Chinese landracepools as morphologically and genetically unique. The Shaanxi pool does not havethe same unique morphological or genetic features, nor is it more similar to thelandrace pools than other improved germplasm pools.     

Über die Sorptionseigenschaften von Waldböden bezüglich gelöster organischer Substanzen

About the sorption of dissolved organic matter to forest soils This investigation characterizes the major forest soils of the temperate climatic zones (leptosols, vertisols, cambisols, luvisols, podzols, stagnosols, gleysols) as sorbents for dissolved organic matter (DOM). Sorption isotherms were obtained for 135 soil horizons from 36 profiles. When solutions containing no DOC were added, the release of dissolved organic carbon (DOC) was highest for horizons rich in organic C (A and Bh horizons). In subsoil horizons DOC release was much lower. Most of the investigated top soils (A and E horizons) and Bh, Bg, and C horizons showed a weak DOC sorption. This was caused by low contents of sorbents (clay and sesquioxides) and/or high contents of organic C. Organic C seems to reduce the DOC sorption by occupying binding sites. Subsoils rich in clay and sesquioxides like Bs, Bt, and Bw horizons showed a strong retention of DOC. Under the aerobic conditions of the experiments, some of the subsoils of stagnosols and gleysols also showed a strong sorption of DOC. However, in sorption experiments conducted after an anaerobic incubation, the DOC sorption decreased significantly.