4种暖季型草坪草的抗旱性分析

对百喜草、假俭草、狗牙根和结缕草4种暖季型草坪草进行土壤持续干旱,测定叶片水分饱和亏、叶绿素、细胞膜相对透性等生理生化指标,并运用模糊隶属函数法进行抗旱性评价。结果表明:干旱胁迫下,狗牙根的水分饱和亏上升幅度最小,而土壤含水量显著高于其他品种,表明狗牙根的抗旱机制主要为保持体内高水势的御旱机制上;狗牙根的叶绿素含量下降幅度最小,相对电导率和丙二醛上升幅度也最小;运用隶属函数法得出百喜草、假俭草、狗牙根和结缕草的隶属函数值分别为:0.506、0.501、0.566和0.537,表明抗旱性强弱为狗牙根结缕草百喜草假俭草;在适合暖季型草坪草生长的干旱地区,狗牙根可以作为培植草坪的首选品种。     

暖季型草坪草光合蒸腾速率日变化研究

百喜草光合速率日变化曲线呈"单峰型",其它3种暖季型草坪草光合速率日变化曲线均为"双峰型",有明显的"午休"现象,日平均光合速率百喜草>假俭草>普通狗牙根>中华结缕草。中华结缕草蒸腾速率日变化曲线呈"单峰型",其它3种暖季型草坪草蒸腾速率日变化曲线均为"双峰型",日平均蒸腾速率百喜草>普通狗牙根>假俭草>中华结缕草,"午休"现象不明显。不同生态因子对四种暖季型草坪草的光合速率、蒸腾速率影响不同。     

5种暖季型草坪草在临沂市的应用评价

为筛选适合临沂地区生长的优良暖季型草坪草品种。对狗牙根、结缕草、沟叶结缕草、假俭草、野牛草5种暖季型草坪草和对照草种冷季型草坪高羊茅进行了田间小区试验,通过草坪密度、质地、颜色、耐寒性、耐旱性、生长速率6个指标综合评价。结果表明:在临沂地区暖季型草坪草综合质量评价明显好于冷季型草坪草,其中狗牙根、结缕草、沟叶结缕草可以在临沂地区进行大范围推广使用。     

低温胁迫下暖季型草坪草质膜透性比较研究

以狗牙根、中华结缕草、假俭草、百喜草4个草种为试验材料,用电导率测定其分别在5℃、0℃、-5℃、-10℃不同低温下12h、24h、36h、48h的电解质外渗率的变化,并对4个草种抗寒过程进行方差分析。结果表明,低温处理后各草种叶片电解质的外渗率呈S型曲线增加。中华结缕草电解质透出率变化缓慢,具有较强的抗寒性。假俭草抗寒性最弱。4种试材抗寒强弱顺序为:中华结缕草>狗牙根>百喜草>假俭草。     

草坪草耐干热低温性能研究

通过测定经干热和低温处理的草坪草样本浸泡液的电导率,结合自然干热、低温条件下的表现,比较冷、暖季型草坪草属间、种间或品种间的耐干热、耐低温性能的差异．结果表明,冷季型草坪草耐干热性能,属间存在着显著差异：羊茅草属＞早熟禾属＞黑麦草属＞翦股颖属;同属的种间大部分也存在着显著差异．暖季型草种中,地毯草、假俭草、狗牙根、细叶结缕草等耐干热性能较为理想;细叶结缕草、黑画眉草、结缕草、鼠尾粟、假俭草等的抗寒性能较强．测试结果与田间观测表现一致,说明测定电导率是检测草坪草耐性的一种简便、快速、有效的方法     

不同暖季型草的坪用生长特性比较

对华南地区种植较广的暖季型草坪草及采集的野生草种共3个属15个草种材料,用田间小区试验和大草坪区辅助观察相结合的办法,进行了坪用生长特征的比较及草坪质量的综合评价。结果表明,在同等养护水平下,结缕草属和假俭草属均具良好的坪用生长特征,假俭草属草种的草坪质量更优于结缕草属;狗牙根属草种的外观形态较差,草坪质量偏低。     

7种暖季型草坪草抗旱性的评价及其生理机制的初步研究

对结缕草、马尼拉、百喜草、钝叶草、假俭草、地毯草与野牛草等暖季型草坪草进行了田间、室内盆栽抗旱性评价。在田间小区试验,通过分步评价法采用叶绿素含量、相对含水量、电导率、冠层温度4个指标比较抗旱性强弱,其顺序依次为:百喜草>野牛草>马尼拉=结缕草>假俭草>钝叶草>地毯草;室内盆栽干旱胁迫试验表明:7种草临界萎蔫点不尽相同,但平均日耗水量大小与萎蔫先后顺序较为一致,且与叶片蒸腾速率之间有显著的相关性。百喜草、地毯草、结缕草3种草的平均日耗水量与蒸腾速率高于其他草种。结缕草、野牛草、马尼拉的保水力显著低于其他草种。这些结果表明:7种草坪草在水分胁迫下存在着不同抗旱机制,有着不同的水分维持能力,通过离体叶片能简单地比较出草坪草耗水量的大小。     

暖季型草坪的春管

暖季型草坪主要包括狗牙根、站缕草、地毡草，假俭草等，适宜于我国西南、华南等热带、亚热带地区种植。这些草种只限于温暖气候条件下生长，在华北地区由于温度较低，对其管理有一定的难度。所以春季暖季型草坪养护管理非常重要。     

优良草坪品种—假俭草

作为草坪种植的草种,按其对温度的要求可分为暖季型草种和冷季型草种两大类.近年来,南京市引进种植的多为冷季型草种.如剪股颖、早熟禾、黑麦草等.这类草种对温度要求较低(地上部分在4℃以上即开始生长),但在南京地区,因夏季气温较高,有休眠现象,病害也较重,故极易造成斑秃,不宜大面积使用.而暖季型草种在长江流域一带只有狗牙根、结缕草等,草种比较单调.根据我们对南京市各公园不同草种生长状况的调查,认为假俭草是一种适应性强、生长     

云南暖地型草坪的建植和养护管理

适合云南热带、亚热带地区栽培的暖地型草坪草种有沟叶结缕草(Zoysiamatressa,又名马尼拉草)、细叶结缕草(Zoysiatenuifosia,又名天鹅绒草)、狗牙根(Cynodondactyson)、大叶油草(Axonopuscompressus,又名地毯草)、假俭草(Eremochloaophiurides)等。目前,我国南方园林绿化中用得     

几种暖季型草坪草的播种试验

对4个暖型草种进行详细的观察研究表明，除结缕草(辽宁)出苗慢，很难成坪外，其他的种均能顺利出苗，且成坪效果好，能形成致密的草坪，质地较好，色泽好，而且具有较强的抗热性和抗病虫害能力，全年绿期均在240d到260d，但其抗寒性有待进一步提高。     

Estimation of the shear strength of wood by uniaxial-tension tests of off-axis specimens

To determine shear strength we conducted uniaxial-tension tests of off-axis specimens and examined the proper off-axis angles. Sitka spruce (Picea sitchensis Carr.) and katsura (Cercidiphyllum japonicum Sieb. and Zucc.) were used for the studies. Uniaxial tension tests of the specimens with various off-axis angles were conducted, and the shear stress at failure was obtained. Independent of the tension tests, torsion tests were conducted, and the shear strengths were obtained. Comparing the data of the uniaxial tension and torsion tests, we examined the validity of estimating shear strength by the off-axis tension test. The shear strengths obtained from the tension tests coincided well with those measured by the torsion tests when the specimen had an off-axis angle of 15°–30°. In this off-axis angle range, the tensile stress perpendicular to the grain might have a serious influence on the shear strength, and we thought that the shear strength predicted by uniaxial tension tests should be treated as an approximate value despite the simplicity of the tension test. Other test methods should be adopted to obtain the precise shear strength of wood.     

Mechanical properties and their interrelationships for medium-density European hardwoods,focusing on ash and beech

ABSTRACT

The usage of hardwoods for engineered wood products, such as glulam, requires defined mechanical properties reflecting the actual tensile strength of the material. Currently, the European strength class system EN 338 only covers profiles for hardwoods tested in bending. In this study, the material properties of medium-density hardwoods are analysed with the focus on a total of 3663 European ash (Fraxinus excelsior) and European beech (Fagus sylvatica) specimens tested in different loading modes (tension, compression, bending, and shear). The relationships between the material properties—tensile strength, stiffness, and density—are analysed on grouped data of both graded and ungraded specimens. As a result, a tailored ratio of tensile strength to tensile MOE and density is given, which allows to utilize a higher tensile strength of hardwoods (f_t,0,k over 30?N/mm²) compared to softwoods. Furthermore, the relationship of the test values and the derived values is checked. The equations for deriving the compression and bending strength from tensile strength are verified based on available data. For tensile and compression strength perpendicular to the grain and for shear strength of both beech and ash, higher strength values than the ones listed in EN 338 are possible. The relationship between the mechanical properties are combined to tensile strength profiles for hardwoods.     

Distribution and tensile strength of Hornbeam (Carpinus betulus) roots growing on slopes of Caspian Forests, Iran

Biomechanical characteristics of the root system of hornbeam (Carpinus betulus) were assessed by measuring Root Area Ratio (RAR) values and tensile strength of root specimens of eight hornbeam trees growing on hilly terrain of Northern Iran. RAR values of the roots were obtained using profile trenching method at soil depth of the top 0.1 m. In total 123 root specimens were analyzed for tensile strength. Results indicate that in general, RAR decreases with depth, following a power function. The RAR values in up and down slopes have no significant statistical differences. In most cases, the maximum RAR values were located in soil depth of the top 0.1 m, with maximum rooting depth at about 0.75 m. The minimum and maximum RAR values along the profiles were 0.004% and 6.431% for down slope and 0.004% and 3.995% for up slope, respectively. The number of roots in the up and down slope trenches was not significantly different. In the same manner as for RAR, number of roots distributing with depth was satisfactorily approximated a power function. The penetration depths of above 90 percent of the roots were at soil depths of 50 cm and 60 cm for up and down slopes, respectively. Results of Spearman's bivariate correlation showed no significant correlation between the RAR value with tree diameter and gradient of slope and number of roots. The mean value of root tensile strength was 31.51 ± 1.05 MPa and root tensile strength decreased with the increase in root diameter, following a power law equation. Using ANCOVA, we found intraspecies variation of tensile strength.     

Distribution and tensile strength of Hornbeam (Carpinus betulus) roots growing on slopes of Caspian Forests, Iran

Biomechanical characteristics of the root system of hornbeam (Carpinus betulus) were assessed by measuring Root Area Ratio (RAR) values and tensile strength of root specimens of eight hornbeam trees growing on hilly terrain of Northern Iran. RAR values of the roots were obtained using profile trenching method at soil depth of the top 0.1 m. In total 123 root specimens were analyzed for tensile strength. Results indicate that in general, RAR decreases with depth, following a power function. The RAR values in up and down slopes have no significant statistical differences. In most cases, the maximum RAR values were located in soil depth of the top 0.1 m, with maximum rooting depth at about 0.75 m. The minimum and maximum RAR values along the profiles were 0.004% and 6.431% for down slope and 0.004% and 3.995% for up slope, respectively. The number of roots in the up and down slope trenches was not significantly different. In the same manner as for RAR, number of roots distributing with depth was satisfactorily approximated a power function. The penetration depths of above 90 percent of the roots were at soil depths of 50 cm and 60 cm for up and down slopes, respectively. Results of Spearman’s bivariate correlation showed no significant correlation between the RAR value with tree diameter and gradient of slope and number of roots. The mean value of root tensile strength was 31.51 ± 1.05 MPa and root tensile strength decreased with the increase in root diameter, following a power law equation. Using ANCOVA, we found intraspecies variation of tensile strength. Biography: Ehsan Abdi (1978– ), Male, Ph.D candidate, in the Department of Forestry, University of Tehran, Karaj 31585-3314, Iran.     

Development of test methods for wooden furniture joints

Abstract

Joints are generally the weakest part of furniture and they are primary cause of failure. To ensure durability and performance of furniture, it is important for a designer to understand the stresses acting on the joints for preparing suitable design and specification of a furniture. Since each type of joint is unique in construction, it is important to know their strength, when subjected to various stresses namely shear, bending, and tensile, by testing the joints. Since there is no established test method for joints, this study was carried out to categorize joints based on their shape, identify the stresses acting over them and develop test methods for testing furniture joints in three modes namely shear, bending, and tension, which are required for designing joints of any furniture and also provide means of comparing strength of different types of joints. Different types of furniture joints were taken for the study and were classified based on their shapes such as L-shaped, T-shaped, straight, and corner joints. Six types of jigs (one type for bending, two types for shear, and three types for tension) were designed and developed for testing the joints, in such a way that any type of joint can be tested in three modes, i.e., bending, shear, and tension using a universal testing machine. The criteria for section of jigs for performing tests on joints, based on their shape and stresses acting on a particular joint, were reported. Tests were carried out using all the six type of jigs to check the suitability of jigs and test methods developed in the study.     

几个暖季型草种的播种试验

通过假俭草、地毯草、百喜草、矮生百慕达等5个暖季型草种的播种试验表明,温度是 暖季型草种发芽的重要因素之一,其它条件相同情况下,低于一定温度(15℃),暖季型草种不 能发芽出苗,在一定温度范围内(15～30℃)范围内,温度愈高,发芽速度愈快;5个草种在堤内 外试验表明,脱壳矮生百慕达播种适应性性状表现最优,假俭草次之,百喜草高生长量大,不适 应护坡要求,地毯草适应性最差。     

The Best Width of Wood Specimen for Zero-span Tension Test

In recent years, the zero-span tension technique of paper and pulp-making industry was applied to wood industry for indirectly testing the longitudinal tensile strength of tracheids. In this paper, this technique was used to test the longitudinal tension strength of tracheids for Chinese fir specimens with different widths. The results showed that average tension strength was 357.39 MPa. The order of average tension strength of tracheids was: 3 mm > 12 mm > 6 mm > 9 mm > 7.5 mm. But, earlywood samples frequ...     

Effect of size and geometry on strength values and MOE of selected hardwood species

The total hardwood timber stock of German forests is fast growing. The lack of knowledge concerning test standards, product standards and sorting criteria makes it difficult to expand the processing and marketing of hardwoods into the field of construction usage. Strength and stiffness data derived from small, defect-free specimens do mostly exist, but in order to be able to insert hardwoods into building applications, data derived from real size specimens is needed. Subsequently, the results of these two different specimen categories need to be correlated and the so-called size effect needs to be quantified and qualified. This paper aims to analyze the size effect of defect-free compression, bending and tensile specimens for the six European hardwood species maple (Acer spp.), birch (Betula pendula), beech (Fagus sylvatica), ash (Fraxinus excelsior), oak (Quercus spp.) and lime (Tilia spp.). They are tested exclusively parallel to grain. Regarding the compression strength for maple, birch and ash, the specimen dimensions did not influence the compression strength value. For beech, oak and lime, it was observed that compression strength increased as the specimen volume was increased. The bending strength of all species decreased as the specimen dimensions increased. Concerning the tensile strength, a clear statement on whether dimensions influence the tensile strength value is not possible. Further research with adjusted specimen sizes, specimen shapes and machine set-ups is needed. Regarding the compression and bending MOE, in most cases, the dimensions did not influence the MOE values. In tensile testing, MOE values differed significantly for the different specimen sizes. Whether these differences were due to slightly different test set-ups in the different sizes or a true size effect could not be answered conclusively.