首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 125 毫秒
1.
INTRoDUCTIONANatoxinsarctoxicsccondarymctabolitCspro-ducedbyAsPergillus~s,A.parastticusandA.nomius(Kurbzmanetal,l987).ThescfUngicangrowreadilyonawidevarictyofagriculturalconunoditicsandPoschealthhazardtobothhumanandanimals.ANa-toxinsareacutClytoxic,carcin…  相似文献   

2.
The effects of long-day photoperiod on growth,photo synthetic fluorescence,carbon and nitrogen metabolism,and yield of Dendrocalamopsis oldhami and the compensation effects of fertilization were investigated.A completely randomized design was used with two light factors(bamboo culms cultivated in solar greenhouse under long-day [Ls] and short-day [Ln] treatments);two organic nitrogen fertilizer levels(application of organic fertilizer[OF] and no organic fertilizer [NF]);and three nitrogen fertil...  相似文献   

3.
The objective was to examine the effects of optimal leaf nitrogen levels> 2.0% and suboptimal levels <2.0%,nitrogen nutrition on net photo synthetic rate,stem diameter increment,height growth increment and acorn mass of pedunculate oak during 2010 in the absence of drought stress and during 2011 under the impact of moderate drought stress.According to the results,moderate drought stress significantly reduced net photo synthetic rate,stem diameter increment and height growth increment,while...  相似文献   

4.
Phytochemical investigation of Beilschmiedia alloiophylla has resulted in the isolation of one new alkaloid, 2-hydroxy-9-methoxyaporphine (1), and ten known natural products, laurotetanine (2), liriodenine (3), boldine (4), secoboldine (5), isoboldine (6), asimilobine (7), oreobeiline (8), 6-epioreobeiline (9), β-amyrone (10), and (S)-3-methoxynordomesticine (11). Chemical studies on the bark of B. kunstleri afforded compounds 2 and 4 along with one bisbenzylisoquinoline alkaloid, N-dimethylphyllocryptine (12). Structures of compounds 1-12 were elucidated on the basis of spectroscopic methods. All of these isolates were evaluated for their anti-acetylcholinesterase (AChE), anti-α-glucosidase, anti-leishmanial and anti-fungal activities. Compounds 1-12 exhibited strong to moderate bioactivities in aforementioned bioassays.  相似文献   

5.
6.
Pretreatment of lespedeza stalks by steam explosion has been studied. The results indicate that steam-exploded pretreatment has strong effects on physical features, morphology, crystallinity, and composition of lespedeza stalks as shown by scanning electron microscopy (SEM), infrared (IR), and X-ray diffraction spectrometry methods. After steam explosion, the cellulose and lignin contents of lespedeza stalks varied only slightly, but the hemicellulose content had decreased from 29.34% to 7.48%. The cellulose obtained by steam-exploded pretreatment had a higher degree of crystallinity than that of the raw material. At the explosion condition of 2.25 MPa and 4 min, lignocellulose is easier to hydrolyze by enzyme than the original lignocellulose. The concentration of reduced sugar in the hydrolyzate liquid increased from 71.77 to 162.84 g·L–1.  相似文献   

7.
The optimal formula of Beta-Cypermethrin aqueous capsule suspension was screened out through the experiment,preparation and manufacture of basic formulas, which has no sedimentation, suspended drops of oil, peels and agglomerating and the diameter of capsule is in range of 10-30μm, conformed to the technical requirement. The aftereffect of the 3.3% Beta-Cypermethrin aqueous capsule suspension which was manufactured according to the optimal formula was up more than 25 days. The experiments on controlling the larvae of Dendrolinmus superans Butler and the adults of Xylotrechus rusticus L were carried out with different concentrations of this chemical. The death rate reached 80% when 250 times solution of the chemical was sprayed on stem to control the larvae of D. superans. For control of the adults of X. rusticus, 200, 400 and 600 times solution of the chemical were applied and their control effects (death rate) reached 85.23%, 74.21% and 66.59% respectively. Two kinds of solution (200 times and 300 times) of the chemical were used to control the larvae of D. superans in large area, and the control effect for both concentrations was over 90%.  相似文献   

8.
Nitrogen is one of the most important elements that can limit plant growth in forest ecosystems. Studies of nitrogen mineralization, nitrogen saturation and nitrogen cycle in forest ecosystems is very necessary for understanding the productivity of stand, nutrient cycle and turnover of nitrogen of forest ecosystems. Based on comparison and analysis of domestic and international academic references related to studies on nitrogen mineralization, nitrogen saturation and nitrogen cycle in recent 10 years, the current situation and development of the study on these aspects, and the problems existed in current researches were reviewed. At last, some advices were given for future researches.  相似文献   

9.
10.
This study investigated the behavior of piezoelectric, dielectric, and elastic constants and the crystallinity in wood cellulose by repeated measurements (n = 42) between 100°C and 220°C. There was an insignificant change in the piezoelectric constant during repeated measurements in this temperature range. On the other hand, thermal decomposition of the amorphous region contributed to the decreasing trend of dielectric and elastic constants, although only a small increase in the elastic constant was found at the time of the initial measurements. The increase in the repeated measurements in this temperature range resulted in an increase in the piezoelectric loss modulus constantd 25, which is closely related to energy loss. Thed 25 peak shifted to a higher temperature with increasing measurements, which might be due not to the increase in rigidity of the wood specimen but to the increase in total peak area, which was observed during the later measurements. At the same time, variations of piezoelectric loss modulusd 25 ande 25 at advanced stages of the measurements suggested damage and structural changes in the wood.  相似文献   

11.
1 INTRODUCTION1.1 Importance of Green AreasAs countries worldwide move toward developingnations, there is a change in education level, employmentand income pattern of their people, which result in higherpurchasing power, better mobility and more free time.With an increase in urbanization as well as rapiddevelopment of infrastructure throughout the countriesthe people are in the transition of changing their lifestyleto modern society.In this urban modern society recreation is becomingincr…  相似文献   

12.
Stand structural complexity enhancement is an increasingly popular management objective,especially on public lands.Complex stand structures are hypothesized to support a relatively high degree of native forest diversity and be more resistant and resilient to disturbances.Complex structures are characterized by the presence of deadwood and heterogeneity of tree-size classes and tree architecture.Relatively little is known about how discrete disturbance events affect structural complexity and compositional diversity in Quercus-dominated stands at fine spatial scales(i.e.neighborhoods).We established 200.05 ha fixed-radius plots on the Sipsey Wilderness of William B.Bankhead National Forest in northern Alabama to quantify woody plant species composition and structure.Trees were mapped on each plot to quantify overstory structural complexity and compositional diversity.We extracted two cores from all canopy Quercus spp.C 5 cm diameter at breast height to quantify age,recruitment pulses,and reconstruct canopy disturbance history.Shannon species diversity in the sampled area was 1.75 for trees,2.08 for saplings,and 1.69 for seedlings.Quercus alba had the greatest basal area,and Ostrya virginiana had the highest density.The stand exhibited a reverse J-shaped distribution with a q-factor of 1.72.The oldest Quercus dated to 1795,and the largest recruitment pulse occurred in the 1870s.The mean return interval for intermediateseverity disturbance was 38 years.Although we documented no relationships between disturbance frequency and compositional diversity at the neighborhood scale(0.05 ha),less frequent disturbance was associated with higher structural complexity(r^2=0.258,p=0.026)at the neighborhood scale.We suggest that localized disturbance increases species diversity and structural complexity,but these processes are manifest at the stand level and not at the neighborhood scale.We conclude that the spatial variability(i.e.size,shape,orientation,microsite conditions)is likely more influential on diversity and complexity than the temporal variation(frequency)of these processes at the neighborhood scale.  相似文献   

13.
Peltophorum dubium seeds were set to imbibe with four treatments, soaked with solution Captan 0.2% under 10and 27℃,PEG 6000 -1.0 MPa under 10 and 27℃. For each treatment there were four replicates with 40 seeds incubated in 9-cm Petri dishes with double filter paper moistened with testing solution. The imbibition curves showed that the final weight increase were from 70% to 150% in the treatments when imbibition entered a lag phase. Seeds were tested for effects on germination of five treatments: control group (nonprimed), primed with PEG6000 -1.0 MPa at 10 and 27℃, primed with Captan 0.2% at 10 and 27℃. For each treatment, there were three sub-treatments: seeds were soaked in distilled water for 12, 24 and 36h before the energy test. Germination percentages of nonprimed seeds and primed in PEG 27℃ soaked in distilled water during 12 h were the highest, reaching 100%. The lowest germination percentage occurred primed seeds with PEG6000 27℃ and soaked in distilled water during 36 h, which was only 52%. Germination mean time of primed seeds in PEG at 10℃, soaked 24 h was 1.08 days, mean time of primed seeds in PEG at 27℃ soaked 12 h was 2.42 days. Accelerated ageing results showed low or no germination after ageing 72 h. Control group had a higher germination percentage and seeds were more resistant to deterioration than those in primed groups, both in Petri dish (27℃) and vermiculate (room temperature).  相似文献   

14.
Balsam fir (Abies balsamea [L.] Mill.), which is widely used for floral greenery, is an important source of nontimber forest products (NTFP) from the northern forests of North America. Nonetheless, additional information is needed to refine and revise commercial tip-harvesting management guidelines to promote sustainable forest management. Therefore, a study was initiated to: (a) examine the socioeconomic impacts of and anticipate the potential biological responses to four contrasting harvesting practices; (b) discuss the implications of the results for the relevance and applicability of some specifications of management guidelines; and (c) assess the compatibility of tip harvesting while pursuing an objective of timber production.  相似文献   

15.
Abstract

Swedish forest commons are collectively owned and managed by shareholders who always also own other forest holdings. The majority of them are non-industrial private forest (NIPF) owners. The objective of this study was to assess differences, with respect to harvesting intensity and related business activities on their individually managed forest properties, between non-shareholders and shareholders in a Swedish forest common. Forest commons are intended to promote local agriculture and forestry and to serve as a model for forestry activities. On this basis, the hypotheses examined in this study were that the shareholders’ harvesting and business activities, as well as their contributions to the local economy, are greater than those of non-shareholders. An apparent difference between shareholders and non-shareholders was found, but it was unexpected since non-shareholders undertook more harvesting and business activities than shareholders, and contributed more to the local economy through taxes. Since no evidence was found for a significant difference between the two categories in their potential to undertake forestry activities, one provisional conclusion is that the outcome is partly due to differences between the institutional frameworks in which shareholders and non-shareholders operate and the impact of these frameworks on incentives to maximize forest production.  相似文献   

16.
Mongolian pine (Pinus sylvestiris Linnaeus var. mongolica Litvinov) as a valuable conifer tree species has been broadly introduced to the sandy land areas in “Three North” regions (North, northwest and northeast of China), but many prob-lems occurred in the earliest Mongolian pine plantations in 7hanggutai, 7hangwu County, Liaoning Province (ZZL). In order to clarify the reason, comprehensive investigations were carried out on differences in structure characteristics, growth processes and ecological factors between artificial stands (the first plantation established in ZZL in 1950s) and natural stands (the origin forests of the tree species in Honghuaerji, Inner Mongolia) on sandy land. The results showed that variation of diameter-class distributions in artificial stands and natural stands could be described by Weibull and Normal distribution models, respectively.Chapman-Richards growth model was employed to reconstruct the growth process of Mongolian pine based on the data from field investigation and stem analysis. The ages of maximum of relative growth rate and average growth rate of DBH, height, and volume of planted trees were 11,22 years, 8, 15 years and 35, 59 years earlier than those of natural stand trees, respectively. In respect of the incremental acceleration of volume, the artificial and natural stands reached their maximum values at 14 years and 33 years respectively. The quantitative maturity ages of artificial stands and natural stands were 43 years and 102 years respectively. It was concluded that the life span of the Mongolian pine trees in natural stands was about 60 years longer than those in artificial stands. The differences mentioned above between artificial and natural Mongolian pine forests on sandy land were partially attributed to the drastic variations of ecological conditions such as latitude, temperature, precipitation, evaporation and height above sea level. Human beings‘‘ disturbances and higher density in plantation forest may be ascribed as additional reasons. Those results may be potentially useful for the management and afforestation of Mongolian pine plantations on sandy land in arid and semi-arid areas.  相似文献   

17.
Following recommendations from studies on land-use issues in the tropics that were carried out by professors of the faculty of agriculture and food sciences, and of the faculty of forestry, geography and geomatics, Université Laval, Canada, a Master’s program in agroforestry was created in 1993 and implemented in 1996. This program of 45 credits leading to a Master’s degree in agroforestry offers two training types: Master of Science (M.Sc.) with thesis and M.Sc. with essay. The M.Sc. with thesis encompasses 21 course-based credits including 6 compulsory credits of internship where the student learns the biophysical, socioeconomic and cultural environments of agroforestry, and 24 research-based credits. The M.Sc. with essay consists of 33 course-based credits including the same 6 compulsory credits of internship, and 12 essay-based credits. Two professors are directly involved in this program, and 35 theses and 19 M.Sc. essays were completed during the period extending from 1996 to February 2014. Fourteen essays and 18 theses investigated biophysical aspects of agroforestry, whereas 5 essays and 17 theses focused on socioeconomic aspects, respectively. Of the 54 thesis and essays that were completed, 61.11 % focused on tropical countries, and 38.89 % on temperate countries. The program also published over 55 peer-reviewed articles, two book chapters and one textbook. The program is expanding in tropical French speaking countries through international projects on training in management of natural resources, and with the use of digital learning tools to reach out more students on-line.  相似文献   

18.
The inhibitory effects of 102 methanol extracts of 40 mycelia, 9 culture fluids, and 53 fruiting bodies of 40 strains of Ganoderma lucidum on 5-reductase were investigated. The methanol extract of the fruiting body of each strain was found to show the strongest 5-reductase inhibitory activity among the extracts tested.  相似文献   

19.
The antifungal effects of citral, eugenol, nerolidol and α-terpineol on Trichophyton mentagrophytes were investigated. Citral over 0.1 mg/ml strongly inhibited the hyphal growth of T. mentagrophytes, and the antifungal activity of α-terpineol was less effective. The morphological changes of the fungus exposed to the terpenes were observed by electron microscopy. The hyphae were distorted and collapsed at 0.2, 0.4 and 1 mg/ml of eugenol, nerolidol and α-terpineol respectively, and cell membrane and organelles were irreversibly damaged at 0.2 mg/ml citral.  相似文献   

20.
Abstract

The present work was conducted to study the effects of wood species, particle size and residue particle size obtained from trimming of wood–cement composites on physical and mechanical properties of cement-bonded particleboard (CBPB). Particleboard was manufactured with a wood/cement ratio of 1:3 and specific gravity 1200 kg m?3. After manufacturing, the boards were tested. The second order plan was used to test the significant difference between factors and levels. It was shown that slenderness and compaction ratio increased and bulk density and specific surface decreased with the increase of particle size. With the increase in slenderness ratio and compaction ratio and decrease in bulk density and specific surface, thickness swelling and mechanical properties improved, but water absorption by the board increased. The addition of 6% of 5/3 fraction size of particle obtained from trimming of boards improved significantly the properties of the boards. The optimized panel properties, obtained using poplar particles with a fraction size of 7pass/on5, exceeded the BISON type HZ and EN Standard for Wood Particleboard. CBPB made of alder or poplar particles with 5/3 fraction size of residue exceeded the BISON type HZ. All CBPB with 5/3 fraction size of residue showed lower mean values of thickness swelling, well below the maximum requirements of both standards. In addition, wood species, fraction size of particles and residue size are believed to have been the main cause of change in the properties of the boards.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号