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Eight populations of Sitka spruce (Picea sitchensis (Bong.) Carr.) and interior spruce (Picea glauca (Moench) Voss x Picea engelmannii Parry ex. Engelm.) seedlings were sampled from a zone of Sitka-interior spruce introgression in British Columbia, Canada. Restriction fragment length polymorphisms of the nuclear ribosomal RNA genes (rDNA) were used to define species-specific hybridization patterns for the Sitka spruce and interior spruce populations. Hybridization was estimated from an index based on the relative abundance of polymorphic rDNA combining bands for each population. Sitka x interior hybrid seedlings had an index value for the relative abundance of interior spruce rDNA (Si-rDNA) ranging from 0.07 (Lower Nass; the most westerly collected source) to 0.95 (Bulkley Valley low-elevation seed orchard). During shoot elongation, osmotic potential at saturation (Psi(sat)) and turgor loss point (Psi(tlp)) increased, whereas total turgor (Psi(PTotal)) decreased. After bud set in the summer and throughout the fall, Psi(sat) and Psi(tlp) decreased, whereas Psi(PTotal) increased. At all times of year, populations with a higher Si-rDNA index had lower Psi(tlp) and Psi(sat) and higher Psi(PTotal) than populations with a lower Si-rDNA index. During the fall, Sitka x interior hybrid seedlings exhibited a seasonal decline in the temperature causing 50% needle electrolyte leakage (LT(50)) and in the critical temperature indicating the initial point of freezing injury. Seedlings with a higher Si-rDNA index had lower LT(50) and critical temperature values indicating greater freezing tolerance in the fall. Throughout most of the year, seedling population Si-rDNA index was related to the degree of drought and freezing tolerance. 相似文献
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Corinne Valdivia M. Kengo Danda Dekha Sheikh Harvey S. James Jr. Violet Gathaara Grace Mbure Festus Murithi William Folk 《Agriculture and Human Values》2014,31(4):673-681
Genetically modified (GM) cassava is currently being developed to address problems of diseases that threaten the food security of farmers in developing countries. The technologies are aimed at smallholder farmers, in hopes of reducing the vulnerability of cassava production to these diseases. In this paper we examine barriers to farmers’ voice in the development of GM cassava. We also examine the role of a translational research process to enhance farmers’ voice, to understand the sources of vulnerability farmers in a group in Kenya’s Coast face, and to determine if their concerns are consistent with those of the scientists in agriculture addressing farmers’ needs. A two-way communication participatory process provided insights into the complex vulnerability context of farmers, their primary concerns with processing and markets of cassava in order to improve livelihoods, the lack of networks with two way communication flows, and the lack of information on GM technologies. The translational research engaged farmers and scientists in an iterative process where scientists are learning what farmers need, and farmers are learning about the potential benefits and risks from GM technologies, while at the same time expressing their concerns. 相似文献
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Information is lacking on how yellow-cedar (Chamaecyparis nootkatensis (D. Don.) Spach) stecklings compare with seedlings in their response to potentially limiting field site environmental conditions. Before planting, yellow-cedar seedlings and stecklings were characterized at 5 and 22°C root temperatures for gas exchange parameters (n=6), root growth capacity (n=12) and plant water movement (n=6) using a fully randomized design in a controlled environment growth room. Seedlings, compared with stecklings (t-test), showed a faster (p=0.01) recovery of net photosynthesis (Pn) and stomatal conductance (gwv) after root temperature increased from 5 to 22°C. Seedlings had greater (p=0.05) root growth capacity (number of new roots 0.5 cm in length) than stecklings after 14 days at 22°C and after 14 days at 5°C followed by 15 days at 22°C. Seedlings had a lower (p=0.01) resistance to plant water movement measured after 29 days (14 days at 5°C followed by 15 days at 22°C root temperature).Seedlings and stecklings were planted on a coastal British Columbia field site and monitored for 1) morphological development and physiological response to ambient site conditions throughout the first growing season, and 2) physiological response to drought conditions during late summer. Both trials used a fully randomized design and stock type means were compared using t-tests (p=0.10, 0.05, and 0.01). Initially, seedlings were taller (p=0.01) than stecklings but otherwise morphologically similar (n=20). Over a 35 week period after planting, stecklings had greater incremental height growth, while seedlings produced a greater (p=0.01) number of roots extending out of the root plug. Seedlings and stecklings (n=6) had similar Pn and gwv patterns under late spring environmental conditions. However, seedlings had greater Pn and gwv under cold temperature (p=0.05 and p=0.1, respectively) and drought conditions (p=0.05 and p=0.01, respectively), but during conditions of high evaporative demand and adequate soil moisture, stecklings had greater (p=0.01) Pn and gwv. Seedlings had higher (p=0.01) daily integrated shoot water potential values (D) at different times during the growing season, and maintained higher (p=0.05) predawn (pd) shoot water-potential values, higher (D) (p=0.01) and lower (p=0.01) resistance to plant water movement (RSPAC) during drought conditions. 相似文献
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Koppens FH Folk JA Elzerman JM Hanson R van Beveren LH Vink IT Tranitz HP Wegscheider W Kouwenhoven LP Vandersypen LM 《Science (New York, N.Y.)》2005,309(5739):1346-1350
We observed mixing between two-electron singlet and triplet states in a double quantum dot, caused by interactions with nuclear spins in the host semiconductor. This mixing was suppressed when we applied a small magnetic field or increased the interdot tunnel coupling and thereby the singlet-triplet splitting. Electron transport involving transitions between triplets and singlets in turn polarized the nuclei, resulting in marked bistabilities. We extract from the fluctuating nuclear field a limitation on the time-averaged spin coherence time T2* of 25 nanoseconds. Control of the electron-nuclear interaction will therefore be crucial for the coherent manipulation of individual electron spins. 相似文献
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An operational assessment of stock quality, prior to field planting, usually includes measures of morphology and a test for root growth capacity (RGC) conducted under optimum conditions. When measured under optimum conditions and interpreted with regard to seedling phenology, performance attributes, such as RGC, provide valuable information about the functional integrity of stock at the time of measurement. However, reforestation sites are rarely associated with optimum growing conditions, and performance attributes measured under optimum conditions provide limited information about field performance potential. Due to these limitations, testing programs at the Forest Biotechnology Centre (BCRI) have used limiting environmental conditions to represent the planting site. This concept is based on the philosophy that tests under limiting environmental conditions will define seedling tolerance and/or resistance to conditions that prevail on the planting site, and hence, better forecast field performance potential. Evidence supporting this concept is presented in three case studies and other cited studies, where performance attributes were measured under a range of limiting environmental test conditions. A performance attribute response model is then presented to define the relationship between testing conditions and field performance potential forecasting. Applicability of this testing approach to operational reforestation programs is discussed. 相似文献
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Western red cedar (Thuja plicata Donn) seedlings were grown in a greenhouse and subjected to six nursery cultural treatments (long-day wet (LDW), long-day moderate (LDM), long-day dry (LDD), short-day wet (SDW), short-day moderate (SDM), and short-day dry (SDD)) during mid-summer. Seedling attributes were measured before fall and spring planting.Short-day and moisture stress treatments reduced shoot but not root growth, resulting in reduced shoot to root ratios. Fall tested LDW seedlings had a higher osmotic potential at saturation and turgor loss point than other treatments. Fall tested short-day seedlings had lower resistance to plant water movement. The LDW seedlings had the greatest new root growth in fall testing, while one of the lowest in spring testing. In the fall, LDW seedlings had the greatest net photosynthesis (Pn) at 25 °C root temperature, with all treatments having a similar decline in Pn as root temperatures decreased to 1 °C. In the spring, all treatments had a similar decline in Pn with decreasing predawn shoot water potential. Moisture stress and short-day nursery cultural treatments applied in mid-summer will not harden western red cedar seedlings for all potential field conditions.Spring, compared to fall, tested seedlings had two times the shoot and three times the root dry weight. Spring tested seedlings had a lower osmotic potential, maximum modulus of elasticity, relative water content at turgor loss point and greater dry weight fraction. Fall, compared to spring, tested seedlings had lower resistance to plant water movement and greater cuticular transpiration. In general, fall tested seedlings had more root growth than spring tested seedlings. Spring, compared to fall, tested seedlings generally had greater stress resistance. 相似文献
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One-year-old interior spruce (Picea glauca (Moench) Voss × Picea engelmannii Parry) spring-stock and summer-stock were grown under two phosphorus (P) fertility regimes, with (+P) or without (–P), followed by a simulated winter, and a second growing period under an adequate fertility regime in a controlled environment room. The two stock-types differed in their response to low P availability. For spring-stock, morphological development, phosphorus-use efficiency (PUE) and P specific absorption rate (SAR) were similar between –P and +P seedlings. For summer-stock, –P seedlings compared to +P seedlings had lower (p 0.05) morphological development, but greater PUE and SAR. For both stock-types, P content increased in +P seedlings, remained low in –P seedlings, and P concentration decreased in nursery-needles (i.e., formed in the nursery) of –P seedlings. The difference in stock-type response to low phosphorus availability (–P) was attributed to internal supply of P and it's retranslocation. Assimilation (A) of CO2 in nursery-needles was similar between –P and +P seedlings for both stock-types. For spring-stock, +P seedlings had greater A in new-needles (i.e., needles formed during the trial) than –P seedlings. It was recommended that the spring-stock be selected over summer-stock for sites low in P availability. 相似文献
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We demonstrate a quantum coherent electron spin filter by directly measuring the spin polarization of emitted current. The spin filter consists of an open quantum dot in an in-plane magnetic field; the in-plane field gives the two spin directions different Fermi wavelengths resulting in spin-dependent quantum interference of transport through the device. The gate voltage is used to select the preferentially transmitted spin, thus setting the polarity of the filter. This provides a fully electrical method for the creation and detection of spin-polarized currents. Polarizations of emitted current as high as 70% for both spin directions (either aligned or anti-aligned with the external field) are observed. 相似文献
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