Tree plantations on farms: Evaluating growth and potential for success

Interest in native species is growing across the tropics as reforestation of degraded lands becomes more widespread. In this study four tree species native to Panama - Cedrela odorata, Pachira quinata, Samanea saman, and Tabebuia rosea - were grown on rural farms at two dry tropical sites in Panama for up to five years. Survivorship and growth data at these “on-farm” trials are compared to data recorded from nearby experimental or “species selection” trial sites and evaluated in terms of soil fertility and management. Participant farmers were also asked about their interest in planting trees in general as well as their interest in 61 species grown in the species selection trial.Although, on-farm survivorship was variable and generally lower than that found on the species selection trial, one species (S. saman) experienced high and consistent survivorship. High survivorship combined with growth data from farms at both sites for this species suggests it would be a good candidate for extension projects working with rural farmers. Survivorship of other species appears more sensitive to farmer management and/or local site conditions. Generally lower growth on the Los Santos farms as compared to the species-selection trial is attributed to the lower soil fertility (plant available P) at the on-farm sites compared to the species selection trial. In contrast, only one species - P. quinata - had a growth variable found to be significantly lower between the on-farm and species selection trial sites in Rio Hato. C. odorata, P. quinata T. rosea can all be used in on-farm conditions with consideration to specific site and management conditions.By 2009, approximately 80% of the farmers planting trees still wished to participate in tree planting activities. All of the farmers no longer wishing to continue with the project expressed slow growth rates of trees as a principal reason. All but one of these farmers had growth rates for his/her trees markedly below those of the species selection trial nearby. Some farmers wishing to continue had very high mortality rates (>70% for all species), suggesting non-tangible benefits for participating in project activities. Other species that were not tested on-farm but grew well in the species-selection trials and were of interest to local farmers are discussed.As long as specific site and management conditions are carefully considered, data from species selection trials can be useful in informing tree planting projects with rural farmers; however, care should be taken to manage expectations.     

Rapid Determination of Mercury in Plant and Soil Samples Using Inductively Coupled Plasma Atomic Emission Spectroscopy, a Comparative Study

The objectives of this study were to simplify sample preparation and validate mercury detection in soil and plant samples using inductively coupled plasma atomic emission spectroscopy (ICP-AES). A set of mercury contaminated and mercury free soil and plant samples were digested and analyzed by ICP-AES, inductively coupled plasma mass spectrometry (ICP-MS), and cold vapor atomic absorption spectroscopy (CVAAS). Results show that mercury measurements in soil and plant samples using ICP-AES were in agreement with those analyzed using ICP-MS and CVAAS. The concentrations of mercury in soils and plant tissues determined by ICP-AES were 92.2% and 90.5% of those determined by CVAAS and ICP-MS, respectively. Digestion of soil samples with 4 M HNO₃ and direct measurement by ICP-AES without reduction of Hg²⁺ to Hg⁰ gave a reasonable and acceptable recovery (92%) for determining Hg in soils. We conclude that ICP-AES with optimized conditions (addition of gold chloride, extension of washing time, linear working range, and selection of wavelength – 194 nm) resulted in reliable detection of mercury in environmental samples.     

Whither or wither microbicides?

After disappointing results from all efficacy trials conducted to date, the field of microbicides research now faces substantial challenges. Poor coordination among interested parties and the choice of nonvalidated scientific targets for phase III studies have hampered progress and created mistrust about the use of microbicides as a method to prevent HIV-1 sexual transmission. Although new promising strategies are available, there will need to be serious reappraisals of how decisions are made to advance the next generations of candidates into clinical trials, and the use of appropriate animal models in this process will be critical.     

When fear is near: threat imminence elicits prefrontal-periaqueductal gray shifts in humans

Humans, like other animals, alter their behavior depending on whether a threat is close or distant. We investigated spatial imminence of threat by developing an active avoidance paradigm in which volunteers were pursued through a maze by a virtual predator endowed with an ability to chase, capture, and inflict pain. Using functional magnetic resonance imaging, we found that as the virtual predator grew closer, brain activity shifted from the ventromedial prefrontal cortex to the periaqueductal gray. This shift showed maximal expression when a high degree of pain was anticipated. Moreover, imminence-driven periaqueductal gray activity correlated with increased subjective degree of dread and decreased confidence of escape. Our findings cast light on the neural dynamics of threat anticipation and have implications for the neurobiology of human anxiety-related disorders.     

Identification of the cystic fibrosis gene: chromosome walking and jumping

An understanding of the basic defect in the inherited disorder cystic fibrosis requires cloning of the cystic fibrosis gene and definition of its protein product. In the absence of direct functional information, chromosomal map position is a guide for locating the gene. Chromosome walking and jumping and complementary DNA hybridization were used to isolate DNA sequences, encompassing more than 500,000 base pairs, from the cystic fibrosis region on the long arm of human chromosome 7. Several transcribed sequences and conserved segments were identified in this cloned region. One of these corresponds to the cystic fibrosis gene and spans approximately 250,000 base pairs of genomic DNA.     

东北内蒙主要用材树种的种源选择

以长白落叶松、兴安落叶松、樟子松、红松、红皮云杉、胡桃楸、水曲柳7个主要用材树种的种源选择进行了全面地、系统地、综合地分析与总结。主要对各树种的早期选择,种源遗传稳定性研究及最佳种源选择等3个方面进行研究。分析结果:种源选择不仅为各造林地区提供了最佳种源,而且也为今后各树种的遗传改良、种子调拔、良种基地建设提供了可靠的依据。     

Infrared echoes near the supernova remnant Cassiopeia A

Two images of Cassiopeia A obtained at 24 micrometers with the Spitzer Space Telescope over a 1-year time interval show moving structures outside the shell of the supernova remnant to a distance of more than 20 arc minutes. Individual features exhibit apparent motions of 10 to 20 arc seconds per year, independently confirmed by near-infrared observations. The observed tangential velocities are at roughly the speed of light. It is likely that the moving structures are infrared echoes, in which interstellar dust is heated by the explosion and by flares from the compact object near the center of the remnant.     

Unwinding of duplex DNA from the SV40 origin of replication by T antigen

The T antigen specified by SV40 virus is the only viral-encoded protein required for replication of SV40 DNA. T antigen has two activities that appear to be essential for viral DNA replication: specific binding to duplex DNA at the origin of replication and helicase activity that unwinds the two DNA strands. As judged by electron microscopy, DNA unwinding is initiated at the origin of replication and proceeds bidirectionally. Either linear or circular DNA molecules containing the origin of replication are effective substrates; with closed circular DNA, a topoisomerase capable of removing positive superhelical turns is required for an efficient reaction. Presence of an origin sequence on duplex DNA and a single-strand DNA-binding protein appear to be the only requirements for T antigen to catalyze unwinding. This reaction mediated by T antigen defines a likely pathway to precise initiation of DNA replication: (i) the sequence-specific binding activity locates the origin sequence, (ii) the duplex DNA is unwound at this site, and (iii) the DNA polymerase and primase begin DNA replication. A similar pathway has been inferred for the localized initiation of DNA replication by bacteriophage lambda and by Escherichia coli in which a sequence-specific binding protein locates the origin and directs the DnaB helicase to this site. Observations with the SV40 system indicate that localized initiation of duplex DNA replication may be similar for prokaryotes and eukaryotes.