痕量灌溉管不同埋深对日光温室沙培黄瓜的影响

以微喷灌溉(CK)为对照,研究痕量灌溉管在沙培中不同埋深对日光温室春季黄瓜生长、产量和水分生产效率等的影响.结果表明,T3处理(25cm)的黄瓜生长与CK(微喷)相比受到显著抑制,T1 (5cm)、T2(15cm)处理黄瓜生物积累量、叶片净光合速率、果实品质与CK相比均有所提高,不同处理间叶片电导率、MDA、根系活力差异不显著,T1、T2、T3处理沙子含水量均低于CK;T1处理的产量比T2处理提高了1.9％;与CK相比的T1、T2处理水分生产效率分别提高50.9％、60.0％.分析表明,日光温室沙培黄瓜栽培中痕量灌溉管埋设深度为5 cm最佳.     

Is the decline of soil microbial biomass in late winter coupled to changes in the physical state of cold soils?

During winter when the active layer of Arctic and alpine soils is below 0 °C, soil microbes are alive but metabolizing slowly, presumably in contact with unfrozen water. This unfrozen water is at the same negative chemical potential as the ice. While both the hydrostatic and the osmotic components of the chemical potential will contribute to this negative value, we argue that the osmotic component (osmotic potential) is the significant contributor. Hence, the soil microorganisms need to be at least halotolerant and psychrotolerant to survive in seasonally frozen soils. The low osmotic potential of unfrozen soil water will lead to the withdrawal of cell water, unless balanced by accumulation of compatible solutes. Many microbes appear to survive this dehydration, since microbial biomass in some situations is high, and rising, in winter. In late winter however, before the soil temperature rises above zero, there can be a considerable decline in soil microbial biomass due to the loss of compatible solutes from viable cells or to cell rupture. This decline may be caused by changes in the physical state of the system, specifically by sudden fluxes of melt water down channels in frozen soil, rapidly raising the chemical potential. The dehydrated cells may be unable to accommodate a rapid rise in osmotic potential so that cell membranes rupture and cells lyse. The exhaustion of soluble substrates released from senescing plant and microbial tissues in autumn and winter may also limit microbial growth, while in addition the rising temperatures may terminate a winter bloom of psychrophiles.Climate change is predicted to cause a decline in plant production in these northern soils, due to summer drought and to an increase in freeze-thaw cycles. Both of these may be expected to reduce soil microbial biomass in late winter. After lysis of microbial cells this biomass provides nutrients for plant growth in early spring. These feedbacks, in turn, could affect herbivory and production at higher trophic levels.     

油松容器苗枯梢症的预防

在玛可河林业局育苗基地油松容器苗的培育过程中,发现有枯梢症发生,通过分析发生的主要原因,对油松枯梢症采取了预防措施,取得了明显效果.     

Combining ability between lines of Cucumis sativus L. and Cucumis sativus var. hardwickii (R.) Alef

Summary Three Cucumis sativus L. (CS) lines adapted to USA growing conditions were used as female parents in crosses to one line each of seven Cucumis sativus var. hardwickii (R.) Alef. (CH) accessions used as male parents to determine the relative combining ability of the CH accessions for six horticultural characters. The 21 F₁ progenies were grown in a randomized complete block design in two locations and evaluated for fruit number, lateral branch number, fruit length, fruit length/diameter ratio, number of female flowering nodes, and days to anthesis. General combining ability (GCA) was significant for all characters in each location. Specific combining ability (SCA) was significant for all characters except days to anthesis in one location and lateral branch number in both locations. Significant location × combining ability interactions were also evident for several characters. Results suggest that CH may be useful for improving fruit yield in commercial cucumber, but that limitations may lie in the attainment of acceptable fruit.Research supported by the College of Agric. and Life Sci., Univ. of Wisconsin, Madison; USDA, ARS, and by funds from Pickle Packers Intl., Inc. Mention of a trademark, proprietary product, or vendor does not constitute a guarantee of warranty of the product by the USDA and does not imply its improval to the exclusion of the other products or vendors that may also be suitable.     

Soil nitrogen mineralization not affected by grass species traits

Species N use traits was evaluated as a mechanism whereby Bromus inermis (Bromus), an established invasive, might alter soil N supply in a Northern mixed-grass prairie. We compared soils under stands of Bromus with those from three representative native grasses of different litter C/N: Andropogon gerardii (Andropogon), Nassella viridula (Nassella) and Pascopyrum smithii (Pascopyrum); in ascending order of litter quality. Net mineralization (per g soil N) measured in year-long laboratory incubations showed no differences in comparisons of Bromus with two of the three native grasses: Andropogon and Nassella. Higher mineralization in Pascopyrum stands relative to Bromus was consistent with its higher litter quality. However, an unusually high occurrence of an N-fixing legume in Pascopyrum stands, potentially favoring high mineralization rates, confounded any conclusions regarding the effects of plant N use on N mineralization. Instead of an initial flush of net mineralization, as would be expected in laboratory incubation, we observed an initial lag phase. This lag in net N mineralization coincided with high microbial activity (respiration) that suggests strong N limitation of the microbial biomass. Further support for the importance of immobilization initially came from modeling mineralization dynamics, which was explained better when we accounted for microbial growth in our model. The absence of strong differences in net mineralization beneath these grasses suggests that differences in plant N use alone were unlikely to influence soil N mineralization through substrate quality, particularly under strong N control of the microbial biomass.     

Quantitation of transgenic plant DNA in leachate water: real-time polymerase chain reaction analysis

Roundup Ready (RR) genetically modified (GM) corn and soybean comprise a large portion of the annual planted acreage of GM crops. Plant growth and subsequent plant decomposition introduce the recombinant DNA (rDNA) into the soil environment, where its fate has not been completely researched. Little is known of the temporal and spatial distribution of plant-derived rDNA in the soil environment and in situ transport of plant DNA by leachate water has not been studied before. The objectives of this study were to determine whether sufficient quantities of plant rDNA were released by roots during growth and early decomposition to be detected in water collected after percolating through a soil profile and to determine the influence of temperature on DNA persistence in the leachate water. Individual plants of RR corn and RR soybean were grown in modified cylinders in a growth room, and the cylinders were flushed with rain water weekly. Immediately after collection, the leachate was subjected to DNA purification followed by rDNA quantification using real-time Polymerase Chain Reaction (PCR) analysis. To test the effects of temperature on plant DNA persistence in leachate water, water samples were spiked with known quantities of RR soybean or RR corn genomic DNA and DNA persistence was examined at 5, 15, and 25 degrees C. Differences in the amounts and temporal distributions of root-derived rDNA were observed between corn and soybean plants. The results suggest that rainfall events may distribute plant DNA throughout the soil and into leachate water. Half-lives of plant DNA in leachate water ranged from 1.2 to 26.7 h, and persistence was greater at colder temperatures (5 and 15 degrees C).     

Acute effects of wood-pulp on sockeye salmon (Oncorhynchus Nerka)

Freshwater suspensions of pulp fiber in concentrations exceeding 1000 ppm at 15°C are acutely lethal to sockeye salmon fingerlings. Limited adaptation of such fish to fiber is possible but injury, at least in the short term, is irreversible. The acute lethality of various toxicants associated with industrial pulps is synergistically enhanced by the presence of fiber, and pulp storage up to 158 days at 15°C had no significant effect on the acute lethality. Highly purified fibers are less toxic in fresh than in sea water. The sensitivity to fiber of fish from two sources did not differ significantly.     

Differentiation of physical from chemical toxicity in solid waste fish bioassays

This study showed that particulate (i.e., physical) toxicity was responsible for rainbow trout deaths in bioassays with two separate solid wastes. This conclusion was based on: (1) fish necropsies which indicated physical damage to gills but no evidence of chemical damage to liver or kidney, (2) chemical analyses which indicated that levels of Priority Pollutants and other target compounds were too low to cause the observed toxicity, (3) structural and chemical analyses of the waste particles which showed that these consisted of inert materials, and (4) the use of centrifugation techniques to remove most of the suspended particulate material in bioassay tanks resulting in an elimination of most of the toxicity. The particles associated with the lethal effects were approximately 5 to 10 μm in size. Regulatory testing of solid wastes must distinguish physical and chemical toxicity since disposal options can vary depending on the mode of toxicity. For instance, chemical toxicity raises concern regarding leaching through soils into groundwater, whereas if physical particles are responsible for toxicity, such leaching is not of concern.