Effects of soil bulk density on seminal and lateral roots of young maize plants (Zea mays L.)     

Rolf O. Kuchenbuch  Keith T. Ingram 《植物养料与土壤学杂志》2004,167(2):229-235

It is well established that increasing soil bulk density (SBD) above some threshold value reduces plant root growth and thus may reduce water and nutrient acquisition. However, formation and elongation of maize seminal roots and first order lateral (FOL) roots in various soil layers under the influence of SBD has not been documented. Two studies were conducted on a loamy sand soil at SBD ranging from 1.25 g cm^–3 to 1.66 g cm^–3. Rhizotrons with a soil layer 7 mm thick were used and pre‐germinated plants were grown for 15 days. Over the range of SBD tested, the shoot growth was not influenced whereas total root length was reduced by 30 % with increasing SBD. Absolute growth rate of seminal roots was highest in the top soil layer and decreased with increasing distance from the surface. Increasing SBD amplified this effect by 20 % and 50 % for the top soil layer and lower soil layers, respectively. At the end of the experiment, total seminal roots attributed to approximately 15 % of the total plant root length. Increasing SBD reduced seminal root growth in the lowest soil layer only, whereas FOL root length decreased with SBD in all but the uppermost soil layer. For FOL, there was a positive interaction of SBD with distance from the soil surface. Both, increasing SBD and soil depth reduced root length by a reduction of number of FOL roots formed while the length of individual FOL roots was not influenced. Hence, increasing SBD may reduce spatial access to nutrients and water by (i) reducing seminal root development in deeper soil layers, aggravated by (ii) the reduction of the number of FOL roots that originate from these seminal roots.  相似文献   

Effects of gibberellin A<Subscript>4/7</Subscript>, 6-benzylaminopurine and chlormequat chloride on the number of male and female strobili and immature cones in Chinese pine (<Emphasis Type="Italic">Pinus tabuliformis</Emphasis>) with foliar sprays     

Keith E. Woeste 《林业研究》2011,22(3):353-359

Three kinds of plant growth regulators, gibberellinA 4/7 (GA 4/7 ), 6-benzylaminopurine (BA), and chlormequat chloride (CCC), were evaluated for their ability to promote strobilus and cone production in a Chinese pine (Pinus tabuliformis Carr.) clonal seed orchard. Treatments (0, 250, 500, or 1000 mg L -1 ) were applied during three periods (June- July, July-August and August-September) in 2005. Of the three plant growth regulators, GA 4/7 was the best for promoting flower and cone production. Trees sprayed...  相似文献   

Aroma extract dilution analysis of cv. Meeker (Rubus idaeus L.) red raspberries from Oregon and Washington     

Klesk K  Qian M  Martin RR 《Journal of agricultural and food chemistry》2004,52(16):5155-5161

  相似文献   

Acid deposition: Effects of sulphuric acid at pH 3 on chemical and biochemical properties of bracken litter     

Keith A. Brown 《Soil biology & biochemistry》1985,17(1):31-38

The effects of increased acid deposition on some biochemical and chemical properties of bracken litter overlying a podzolic soil contained in monolith lysimeters were investigated. Pairs of lysimeters each received 1500 mm yr^?1 of “rain” consisting either of distilled water or pH 3.0 sulphuric acid applied evenly over a 5-yr period. The acid-treatment resulted in a marked acidification of the litter, associated with accelerated leaching of Ca²⁺, Mg²⁺, K⁺ and Mn²⁺. Acid treatment also increased the concentration of extractable Al³⁺ in the litter. The biochemical changes observed in the litter as a consequence of acidification included decreases of 33% in ATP content and 54% in respiration rate. Significant reductions in the mineralization rates of urea, glucose and acetate, and in the activities of 4-nitrophenylphosphatase, $\text{β-N-}\text{acetyl-}\text{d}\text{-glucosaminidase}$, exo-1,4,β-d-xylosidase and peroxidase were also observed in the acid-treated litter. The acid-treated litter also contained slightly less total N, ammonium-N and total P, and slightly more residual hexose carbohydrate than the control litter. The effects observed were consistent with a decrease in microbial activity associated with litter acidification and were reflected in a small (5.5%) but significant (P < 0.05) decrease in litter decomposition. Acid treatment decreased the ATP content of the mineral soil by about 13% in the 3 cm immediately beneath the litter, but below this depth no significant difference was observed.  相似文献   

Characterization of organic phosphorus in leachate from a grassland soil     

Gurpal S. Toor  Leo M. CondronHong J. Di  Keith C. CameronBarbara J. Cade-Menun 《Soil biology & biochemistry》2003,35(10):1317-1323

The degree of eutrophication in fresh water ecosystems may be influenced by the forms of phosphorus (P) leached from agricultural systems. Physico-chemical fractionation of P in leachate from a grassland soil carried out over a two year period indicated that the majority of the P loss from the Lismore soil occurred in unreactive particulate (55-76%) P forms. ³¹P nuclear magnetic resonance analysis of a selected leachate sample indicated that unreactive P was mainly comprised of monoester and diester forms of organic P. The presence of phosphomonoesterase (20-200 μg p nitrophenol l⁻¹ h⁻¹) and phosphodiesterase (68 μg bis-p nitrophenol l⁻¹ h⁻¹) activity in leachate resulted in hydrolysis of 10-21% of total unreactive P (TUP), indicating that some of the monoesters and diesters can be eventually hydrolyzed into inorganic P forms during P transport. Enzyme hydrolysis showed that 23% of the TUP was present as labile monoester P (LMP), followed by 20% as inositol hexakisphosphate (IHP) and 14% as diesters (phospholipids and nucleic acids). The findings of this study suggest that LMP, IHP and diesters are an important component of organic P leaching from the grassland soil.  相似文献   

Aerosol and precipitation chemistry relationships at big bend national park     

Michele R. Derrick  Jarvis L. Moyers  Keith A. Yarborough  Mike Warren 《Water, air, and soil pollution》1984,21(1-4):171-181

Aerosol chemistry, precipitation and visibility parameters are currently being measured at Big Bend National Park in Texas. This is part of a large-scale air resource evaluation program which the National Park Service is sponsoring in several southwestern national parks and monuments to determine the potential impact of local and distant pollutant sources on the environmental quality within these areas. Analysis of aerosol samples collected at six sites in the Southwest indicates that soil-derived components, organic materials and the acid-base ions of sulfate, nitrate, and ammonium are the major constituents of suspended airborne particulate matter in the remote areas of the arid region. Comparison of particulate matter chemistry and precipitation chemistry data at Big Bend National Park shows consistent features which indicate that the airborne alkaline soil material and NH₃ largely neutralize the atmospheric acidic species of H₂SO₄ and HNO₃. Given the similarity of the particulate matter composition and loading at the other monitoring sites, it is suggested that the trace chemical composition of precipitation will be similar in many remote regions of the Southwest.  相似文献   

The chemist and the community     

Little AD 《Science (New York, N.Y.)》1980,208(4449):1250

  相似文献   

Isolation of single-copy human genes from a library of yeast artificial chromosome clones   总被引：70，自引：0，他引：70  

B H Brownstein  G A Silverman  R D Little  D T Burke  S J Korsmeyer  D Schlessinger  M V Olson 《Science (New York, N.Y.)》1989,244(4910):1348-1351

A recently developed cloning system based on the propagation of large DNA molecules as linear, artificial chromosomes in the yeast Saccharomyces cerevisiae provides a potential method of cloning the entire human genome in segments of several hundred kilobase pairs. Most application of this system will require the ability to recover specific sequences from libraries of yeast artificial chromosome clones and to propagate these sequences in yeast without alterations. Two single-copy genes have now been cloned from a library of yeast artificial chromosome clones that was prepared from total human DNA. Multiple, independent isolates were obtained of the genes encoding factor IX and plasminogen activator inhibitor type 2. The clones, which ranged in size from 60 to 650 kilobases, were stable on prolonged propagation in yeast and appear to contain faithful replicas of human DNA.  相似文献   

Chernobyl: an overlooked aspect?     

Baverstock K  Williams D 《Science (New York, N.Y.)》2003,299(5603):44

  相似文献   

Public health. Is safe mail worth the price?     

Florig HK 《Science (New York, N.Y.)》2002,295(5559):1467-1468

  相似文献