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11.
12.
Plantations of radiata pine (P. radiata D.Don) on soils previously under legume based pastures have a high incidence of stem deformity compared with forest soils.
A comparison of soil properties and tree nutrition of 5 to 7 year-old radiata pine on former pastures in the first part of
the study showed that stem deformity was strongly correlated with mineralisation of soil N and in particular with nitrification.
Other soil properties that have changed as a result of pasture improvement, e.g. pH, available P and Mn, were only partially
correlated with stem deformity. In the second part of the study, the role of N availability and other soil properties in the
expression of deformity was further investigated in a separate field experiment on soils formerly under native eucalypt forest,
tobacco cropping, and improved pasture. Young radiata pine plantings were treated with lime, phosphorus, and nitrogen applied
as urea and sodium nitrate. Liming increased soil pH by around 1.5 units, raised exchangeable Ca2+ and decreased available Mn. Soil mineral N content was only marginally affected by liming. Superphosphate increased soil
available P and raised levels of P in foliage. Changes in soil pH, availability of P, Mn, and B did not affect growth or stem
deformity at any of the sites. In contrast, application of N fertilisers at 200 and 600 kg N ha-1 increased mineral N content and stimulated nitrification, particularly at the forest site. The high rate of N fertiliser
increased basal area at the forest site by 45%, but also raised the level of stem deformity from 12% to 56%. At the tobacco
and pasture sites, this treatment did not increase growth and did not significantly raise stem deformity above the already
high basic level of deformity (63%). Implications of stem deformity in young plantations of radiata pine on potential utilisation
later in the rotation are discussed. 相似文献
13.
Under certain conditions it is possible in Paramecium cells to induce selectively the fusion of the secretory organelle membrane with the cell membrane without the involvement of any further steps (release of secretory contents, etc.). A Ca2+-mobilizing fusogen was used in the presence of components which inhibit the discharge of the secretory contents (Mg2+ and EGTA, mainly). One can thus produce many exocytotic openings with the secretory contents (which are normally vigorously discharged) still retained. 相似文献
14.
Stephen Phillips Matt Cotten Françoise Laengle-Rouault Gotthold Schaffner Max L. Birnstiel 《Chromosoma》1992,101(9):549-556
The sphere organelles (spheres) ofXenopus and other amphibian oocytes are known to contain small nuclear ribonucleoprotein particles (snRNPs) and have been suggested to play a role in snRNP complex assembly. Coupled with the similarities that exist between spheres and nucleoli and the quantitative and kinetic aspects of snRNA synthesis in theXenopus oocyte, we have investigated whether or not the U snRNA encoding genes are amplified inXenopus oogenesis, the spheres being possible sites for the location of such extrachromosomal gene copies. By applying a number of quantitative nucleic acid hybridization procedures to both total and fractionated oocyte and somatic DNA, employing both homologous and heterologous U snRNA gene probes and suitable amplification and non-amplification control probes, we show that the U snRNA genes do not undergo any major amplification inXenopus oogenesis. Therefore, the analogy between the sphere organelles and nucleoli appears to be limited. The role of the spheres and their relationship to other snRNP containing structures, specifically B snurposomes, and the sphere organizer loci remains obscure.by A. Spradling 相似文献
15.
Quan Zhang Mallory Barnes Michael Benson Elizabeth Burakowski A. Christopher Oishi Andrew Ouimette Rebecca Sanders‐DeMott Paul C. Stoy Matt Wenzel Lihua Xiong Koong Yi Kimberly A. Novick 《Global Change Biology》2020,26(6):3384-3401
Land‐use/cover change (LUCC) is an important driver of environmental change, occurring at the same time as, and often interacting with, global climate change. Reforestation and deforestation have been critical aspects of LUCC over the past two centuries and are widely studied for their potential to perturb the global carbon cycle. More recently, there has been keen interest in understanding the extent to which reforestation affects terrestrial energy cycling and thus surface temperature directly by altering surface physical properties (e.g., albedo and emissivity) and land–atmosphere energy exchange. The impacts of reforestation on land surface temperature and their mechanisms are relatively well understood in tropical and boreal climates, but the effects of reforestation on warming and/or cooling in temperate zones are less certain. This study is designed to elucidate the biophysical mechanisms that link land cover and surface temperature in temperate ecosystems. To achieve this goal, we used data from six paired eddy‐covariance towers over co‐located forests and grasslands in the temperate eastern United States, where radiation components, latent and sensible heat fluxes, and meteorological conditions were measured. The results show that, at the annual time scale, the surface of the forests is 1–2°C cooler than grasslands, indicating a substantial cooling effect of reforestation. The enhanced latent and sensible heat fluxes of forests have an average cooling effect of ?2.5°C, which offsets the net warming effect (+1.5°C) of albedo warming (+2.3°C) and emissivity cooling effect (?0.8°C) associated with surface properties. Additional daytime cooling over forests is driven by local feedbacks to incoming radiation. We further show that the forest cooling effect is most pronounced when land surface temperature is higher, often exceeding ?5°C. Our results contribute important observational evidence that reforestation in the temperate zone offers opportunities for local climate mitigation and adaptation. 相似文献
16.
17.
Sam Moore Edward M. Hill Louise Dyson Michael J. Tildesley Matt J. Keeling 《PLoS computational biology》2021,17(5)
The COVID-19 outbreak has highlighted our vulnerability to novel infections.Faced with this threat and no effective treatment, in line with many other countries, the UK adopted enforced social distancing (lockdown) to reduce transmission—successfully reducing the reproductive number R below one. However, given the large pool of susceptible individuals that remain, complete relaxation of controls is likely to generate a substantial further outbreak. Vaccination remains the only foreseeable means of both containing the infection and returning to normal interactions and behaviour. Here, we consider the optimal targeting of vaccination within the UK, with the aim of minimising future deaths or quality adjusted life year (QALY) losses. We show that, for a range of assumptions on the action and efficacy of the vaccine, targeting older age groups first is optimal and may be sufficient to stem the epidemic if the vaccine prevents transmission as well as disease. 相似文献
18.
19.
Bo Xian Jie Shen Weiyang Chen Na Sun Nan Qiao Dongqing Jiang Tao Yu Yongfan Men Zhijun Han Yuhong Pang Matt Kaeberlein Yanyi Huang Jing‐Dong J. Han 《Aging cell》2013,12(3):398-409
Caenorhabditis elegans is a leading model organism for studying the basic mechanisms of aging. Progress has been limited, however, by the lack of an automated system for quantitative analysis of longevity and mean lifespan. To address this barrier, we developed ‘WormFarm’, an integrated microfluidic device for culturing nematodes. Cohorts of 30–50 animals are maintained throughout their lifespan in each of eight separate chambers on a single WormFarm polydimethylsiloxane chip. Design features allow for automated removal of progeny and efficient control of environmental conditions. In addition, we have developed computational algorithms for automated analysis of video footage to quantitate survival and other phenotypes, such as body size and motility. As proof‐of‐principle, we show here that WormFarm successfully recapitulates survival data obtained from a standard plate‐based assay for both RNAi‐mediated and dietary‐induced changes in lifespan. Further, using a fluorescent reporter in conjunction with WormFarm, we report an age‐associated decrease in fluorescent intensity of GFP in transgenic worms expressing GFP tagged with a mitochondrial import signal under the control of the myo‐3 promoter. This marker may therefore serve as a useful biomarker of biological age and aging rate. 相似文献
20.
Matt Husa Freyr Petursson Martin Lotz Robert Terkeltaub Ru Liu-Bryan 《Arthritis research & therapy》2013,15(6):R218