Effects of site conditions on growth and wood properties of Populus×euramericana cv.'74/76'

The growth and wood properties of 240 individual Populus×euramericana cv.’74/76’(hereafter poplar 107)trees planted in Hebei Plain,China was evaluated.Mean annual increments in height,breast height diameter and volume,as well as cellulose,hemicellulose and lignin contents,shrinkage,density,bending strength and modulus of elasticity in the heart wood and sap wood.Environmental factors influencing growth and wood properties were analyzed using correlation and stepwise regres sion.The results show that the coefficients of variation(CVs)of growth traits ranged from 10.6 to 22.4%.The CVs of the chemical properties of heartwood ranged from 4.3 to 30.2%,and for sap wood from 3.2 to 27.5%.The CVs of the physical and mechanical properties of heartwood ranged from 8.6 to 31.7%,and for sapwood from 6.4 to 29.9%.The results of one-way ANOVA showed that there were significant differences in growth traits and wood properties among sites.Soil pH,total and available phosphorus,total potassium,and soil organic matter were key soil factors affecting growth and wood properties of poplar 107,whereas mean annual ground temperatures and precipitation were the main climatic factors.To better cultivate poplar 107,area with less annual rainfall,slightly higher temperature and soil pH value close to neutral should be selected.

The importance of proleptic branch traits in biomass production of poplar in high-density plantations

Branch phenotypic traits determine tree crown architecture,which in turn governs leaf display,light interception,and biomass production.Sylleptic and proleptic branches are the obviously different branch phenotypes in the poplar crown.Many studies have focused on the influence of sylleptic branch numbers(SBN)on biomass production,but the research on the influence of proleptic branch phenotypes was only a few.To explore the relationship between proleptic branch traits and biomass generation production in a high-density poplar plantation,we investigated the branch phenotypic traits of three poplar genotypes,all of which have high survival rates in forests(>95%)and significantly different crown architecture and biomass performance in the high-density plantations(1667 stems ha−1).The plantation site was established in 2007.A terrestrial laser scanner was used to measure branch characteristics such as length,angle of origin and termination,and azi-muth angle.A hierarchical cluster analysis performed on branch characteristics showed that SBN,crown depth,and proleptic branch curvature(PBC)were clustered with bio-mass production and leaf area index(LAI).Among all of the monitored traits,PBC played the second most important role in biomass production after SBN and was significantly correlated with SBN,LAI,and biomass production.The positive correlation between PBC and SBN indicated that a larger PBC was associated with more sylleptic branches within the monitored genotypes planted in the high-density plantation,providing greater leaf area and biomass produc-tion.The results of this study will improve the identification of high-production poplar varieties for cultivation in high-density plantations for biofuel production.

Morphological and physiological plasticity response to low nitrogen stress in black cottonwood(Populus deltoides Marsh.)

It is important to evaluate nitrogen use efficiency and nitrogen tolerance of trees in order to improve their productivity.In this study,both were evaluated for 338 Populus deltoides genotypes from six provenances.The plants were cultured under normal nitrogen(750μM NH_4 NO_3)and low nitrogen(5μM NH_4 NO_3)conditions for 3 months.Growth,chlorophyll content and glutamine synthetase activity of each genotype were measured.Under low nitrogen,heights,ground diameter,leaf area,leaf and root biomass,and chlorophyll contents were significantly lower than those under normal nitrogen level.Correlation analysis showed that nutrient distribution changed under different nitrogen treatments.There was a negative correlation between leaf traits and root biomass under normal nitrogen level,however,the correlation became positive in low nitrogen treatment.Moreover,with the decrease of nitrogen level,the negative correlation between leaf morphology and chlorophyll levels became weakened.The growth of the genotypes under the two treatments was evaluated by combining principal component analysis with a fuzzy mathematical membership function;the results showed that leaf traits accounted for a large proportion of the variation in the evaluation model.According to the results of comprehensive evaluation of plants under the two treatments,the 338 P.deltoides genotypes could be divided into nine categories,with wide genotypic diversity in nitrogen use efficiency and low nitrogen tolerance.As a result,26 N-efficient genotypes and 24 N-inefficient genotypes were selected.By comparative analysis of their morphological and physiological traits under the two treatments,leaf traits could be significant indicators for nitrogen use efficiency and nitrogen tolerance,which is of considerable significance for breeding poplar varieties with high nitrogen use efficiencies.

Association Analysis of the Growth of Black Poplar (Populus Nigra L.) Under Contrasting Nitrogen Levels

The European black poplar(Populus nigra L.)has been used as a germplasm resource for the breeding of new poplar varieties around the world.The identification and screening of its high nitrogen use efficiency genotypes could enable the breeding of new resource-efficient poplar varieties.The accessions were screened using MALDI-TOF MS genotyping technology for ammonium transporter(AMT)and nitrate transporters(NRT)genes against phenotypic data for seedling height and ground diameter traits,in both low and high nitrogen environments.Allele re-sequencing of seven genes related to root development was carried out using the minisequencing method.By cluster analysis,101 accessions of black poplar were divided into 4 populations,and it was concluded that Central Europe is the origin of the evolution of low-nitrogen and high-efficiency populations of European black poplar.Association study between SNP typing and seedling height and ground diameter traits showed that there were significant correlations between four SNP loci and growth traits under the contrasting N levels.We found that SNP3 and SNP4 in the PttAMT1;3 gene were significantly associated with seedling height traits,and that SNP2 and SNP7 in the PttAMT1;2 and PttAMT1;5 genes,respectively,were significantly associated with ground diameter traits.Thus,considerable allelic diversity is present within the candidate genes studied and can be utilized to develop functional markers to select for poplars with improved growth under N stress conditions.

Assessing bacterial communities in the rhizosphere of 8-year-old genetically modified poplar(Populus spp.)

Microbe communities in rhizosphere ecosystems are important for plant health but there is limited knowledge of them in the rhizospheres of genetically modified（GM） plants, especial for tree species. We used the amplitude sequencing method to analyze the V4 regions of the 16 S r RNA gene to identify changes in bacterial diversity and community structure in two GM lines（D520 and D521）, one non-genetically modified（nonGM） line and in uncultivated soil. After chimera filtering,468.133 sequences in the domain Bacteria remained. There were ten dominant taxonomic groups（with [1 % of all sequences） across the samples. 241 of 551 genera（representing a ratio of 97.33 %） were common to all samples.A Venn diagram showed that 1.926 operational taxonomic units（OTUs） were shared by all samples. We found a specific change, a reduction in Chloroflexi, in the microorganisms in the rhizosphere soil planted with poplars. Taken together, the results showed few statistical differences in the bacterial diversity and community structure between the GM line and non-GM line, this suggests that there was no or very limited impact of this genetic modification on the bacterial communities in the rhizosphere.

A cDNA microarray analysis of the molecular control of poplar wood properties

Molecular biological research into wood development and formation has been the focus in recent years, but the pace of discovery of related genes and their functions in the control of wood properties has been slow. The microarray technique--with its advantages of high throughput capacity, sensitivity, and reliability over other tools developed for investigating genes expression patterns-is capable of rapidly assaying thousands of genes. In this study, a cDNA microarray prepared from two cDNA libraries of developing poplar xylem tissues was used to assay gene expression patterns in immature xylem tissues at different heights from the main stem of Populus deltoides （15 years old）, which was confirmed to have distinct wood properties （microfibrillar angle, woody density） by X-ray. Two hundred seventy-four transcripts with differ- ential expression profles between the chips were screened out, and the individual clones were subjected to 5＇ sequencing. Using bioinformatic analysis, we identified candidate genes that may influence poplar wood properties, many of which belong to various regulatory and signal transduction gene families, such as zinc finger protein transcription factor, DNA-binding transcription factor, ethylene response factors, and so on. The results suggest that these genes may regulate enzymes involved in wood formation. Further work will be performed to clone these genes and determine how they influence poplar wood properties.

No consistent daily variation in DNA methylation detected in Populus nigra leaves by methylation-sensitive amplification polymorphism analysis

DNA methylation, an epigenetic mechanism used by cells to control gene expression, has an important biological role in plant development and environmental fitness. Since plant DNA methylation is closely related to environmental conditions, variation during the day is expected. Here, in genetically identical plants of Populus nigra clone N46, DNA methylation changes in leaves over a 24 h period were detected using the methylation-sensitive amplification polymorphism method. The results showed different DNA methylation patterns in mature poplar leaves: not only in individuals at the same time, but also in samples at each of the six time during the day. In addition, night samples had a higher percentage of methylation than in morning samples. However, no statistically significant differences were found among the samples gathered at different times. Similar results were obtained for three other P. nigra clones with different genetic backgrounds. Real time qPCR showed that the DNA methyltransferase genes Pt-MET1 and Pt-SOM1 involved in CG DNA methylation in poplar were stable over a 24 h period in leaves of P. nigra N46 compared with circadian-controlled genes. That could be part of the reason that methylation of CCGG sites is stable in those leaves. That DNA methylation differed even in genetically identical plants indicates the specificity of DNA methylation changes in their genomes. No statistically significant differences in methylation changes were found between day and night, suggesting that DNA methylation is more stable than expected and is unlikely to be involved in circadian regulation in plants.

Waterlogging tolerance and wood properties of transgenic Populus alba×glandulosa expressing Vitreoscilla hemoglobin gene(Vgb)

Because overexpression of Vitreoscilla hemoglobin gene(Vgb)gene in plants can enhance tolerance to waterlogging,here Vgb was inserted into Populus alba×glandulosa to investigate its expression and effects on growth and physiological responses to waterlogging stress in the transgenic poplars.Southern blotting and RT-PCR analysis of Vgb-transgenic P.alba×glandulosa showed that the Vgb gene was integrated into the genome of the V13-81 and V13-85 transgenic lines and expressed.In greenhouse waterlogging stress tests,mortality of the transgenic poplar was significant lower than that of nontransgenic plants with increasing treatment time from 2 to 22 days.The transgenic plants had higher chlorophyll content and less chloroplast damage than in the control plants.Additionally,starch accumulation increased,and growth was enhanced in the transgenic plants,suggesting that the Vgb-expressing lines had improved energy reserves.Field trials of the transgenic poplar suggested that Vgb expression promotes growth and influences wood quality.Taken together,our results suggest that the expression of Vgb can increase the accumulation of chlorophyll and starch in the transgenic poplar,improve its ability to endure flooding,and improve growth and wood quality of the transgenic plants.

Rigor and Relevance： On the Development of Entrepreneurship Research in China

This study examines the contributions of Chinese entrepreneurship research to academic knowledge and its practical implications. Specifically, we investigate how Chinese entrepreneurship research meets the standards of rigor and relevance based on a review of 64 papers published in five major scholarly journals in the Chinese mainland. Results show that Chinese entrepreneurship research has paid comparatively little attention to the ＂rigor＂ dimension, while focusing more heavily on practical relevance than on academic relevance on the ＂relevance＂ dimension. Future directions for China＇s entrepreneurship research are also discussed.

Identification of EGF as an Important Regulator for Promoting CYP3A4 Expression in Human Embryonic Stem Cell-Derived Hepatocytes Using TALEN-Based Gene Targeting

Functional human hepatocytes are one of the most significant tools for studying drug absorption, distribution, metabolism and excretion/toxicity （ADME/Tox）, especially for applications in preclinical drug development （Sahi et al., 2010; Godoy et al., 2013）. They provide the closest in vitro model to the human liver and the only model that mimics the drug metabolic profiles found in vivo. However, these cells lose their metabolic function rapidly and dramatically during the in vitro culture process, which largely hinders their wider application in drug development （Sahi et al., 2010; Godoy et al., 2013）. To overcome this obstacle, it is important to regulate the activities of key genes which are responsible for the detoxification metabolic function of human hepatocytes.

Entrepreneurial Orientation and Performance of Chinese High-Tech Firms： The Mediating Role of Organizational Learning and Moderating Role of Firm Life Cycle

The evidence about how entrepreneurial orientation （EO） affects firms＇ performance remains inconclusive. This study joins the research by incorporating organizational learning （OL） as a micro-macro link and by extending empirical work to the largely underexplored context of Chinese high-tech industries. Results from a survey of 252 Chinese high-tech firms demonstrate： （1） entrepreneurial orientation is positively related to firm performance; （2） organizational learning is also positively related to firm performance; （3） organizational learning partly mediates the positive impact of entrepreneurial orientation on firm performance; and （4） high-tech companies in the start-up and growth stage are likely to demonstrate stronger linkages in the EO-OL-performance relationship than in mature stage, which shows that the EO-OL-performance relationship is moderated by firms＇ life cycle.