黄土高原不同土地利用方式分层植被的盖度差异

[目的] 分析不同土地利用方式黄土高原植被的覆盖状况,为监测该区植被特别是非绿色植被盖度的变化提供数据支持,为遥感估算植被覆盖度(FVC)在土壤侵蚀预测中的应用提供可靠依据。[方法] 选择黄土高原不同土地利用类型的7块植被样地,采用样带法进行逐半月的分层植被盖度调查,分析了绿色植被盖度(f_PV)和非绿色植被盖度(f_NPV)在不同类型以及不同层次结构下的年内变化,为侵蚀过程模型中植被因素的获取提供参数。[结果] ①沙地、草地、人工柠条林地、人工油松林地、黄陵和秦岭的天然林地等6个样地中,植被的年内投影总盖度变化不大。投影f_PV和其所占投影总盖度的比例年内均随时间先逐渐增加,7—9月达到最大值,其后迅速减小。而投影f_NPV随时间的变化趋势与f_PV相反。受耕作制度影响,耕地投影f_PV和f_NPV年内变化剧烈。②7—9月,在黄陵和秦岭的天然林样地,投影f_PV比例可达100%,其他4种样地分别可达60.6%,70.5%,58.8%和84.9%,意味着仅考虑投影f_PV,将忽略占总盖度39.4%,29.5%,41.2%和15.1%的f_NPV的生态效益。③人工柠条、人工油松林地,黄陵、秦岭的天然林地等4种具有明显植被垂直结构的样地中,乔木层、灌木层和地表层的f_PV与f_NPV的年内变化与投影f_PV与f_NPV的变化趋势基本一致;4种样地植被的投影总盖度与地表层总盖度呈线性关系,其相关性可达0.85(R²)。[结论] 黄土高原不同土地利用方式耕地投影f_PV和f_NPV年内变化剧烈,其他样地年内投影f_PV先增加后减小,投影f_NPV与其相反。占总投影盖度的15.1%～41.2%的投影f_NPV,在该区是不可忽略的地被组成。不同层次的f_PV和f_NPV年内变化趋势与投影f_PV和f_NPV一致,地表层总盖度与投影总盖度也存在显著的线性相关性。在区域监测时应重点关注耕地植被盖度的提取季节与地表总盖度。     

楠木种子处理办法初探

由于楠木种质资源有限,如何充分利用现有的种质资源进行珍稀树种扩繁,是本次试验的主要目的。在恒温条件下(24℃),利用不同浓度的赤霉素溶液处理经过不同层积天数的楠木种子,然后进行发芽试验。结果表明:900 mg/L的赤霉素溶液浸泡层积时间为50 d的种子,其发芽率最高达到92%,与对照相比差异很大,因此适宜的楠木种子处理方法可以显著提高其发芽率。     

UTILIZATION OF FOREST PRODUCTS WITH SPECIAL REFERENCE TO TIMBER-FRAMED HOUSING

The history of professional forestry education in South Africa is shortly outlined, with emphasis on the last few years. Information is presented on syllabus and staff, and on the numbers and scholastic standard of the forestry students.     

Assessing the protective effect of vertically heterogeneous canopies against radiative frost: The case of quinoa on the Andean Altiplano

Night radiative frost is a highly limiting factor for agriculture in Andean highlands. Nevertheless, a diversity of crop species have been domesticated there, commonly showing high heterogeneity in plant growth at the field level. The possible protective effect of crop canopy heterogeneity against nocturnal radiative frost is examined using a dual approach, combining a field experiment and a simplified energy balance model at the leaf level. Leaf and air temperatures were registered over an entire quinoa crop cycle in the Andean highlands of Bolivia, comparing two cultivars: Blanca de Yanamuyu, a traditional landrace with high plant height heterogeneity, and Surumi, a more homogeneous selected variety. In both cultivars, inverted air density profiles during calm and clear nights result in air temperature changes up to 3 °C over 0.5 m height, with minimum air temperature concentrated at the upper part of the canopy. In these conditions, leaf temperature gradients of up to 2.6 °C m⁻¹ develop within the canopy of the traditional landrace, with minimum leaf temperature significantly higher (P < 0.001) in shaded plants of the landrace than in the selected cultivar. A dynamic model of leaf temperature based on canopy parameters and climatic records at screen level adequately simulates leaf temperature differences in the case of a vertically heterogeneous quinoa canopy. A sensitivity analysis of the model reveals that canopy height, leaf area index, and sky cloudiness have the most important influences on the development of the sheltering effect, while air temperature and air humidity play a minor role under typical radiative frost conditions. As for wind speed, its actual influence remains unclear due to experimental and modelling limitations at low wind speeds. The significance of these results is discussed in terms of the trade-off between stress adaptation and biomass productivity.     

膜苞鸢尾种子休眠及萌发特性研究

膜苞鸢尾（Iris scariosa）种子存在休眠。通过萌发抑制物测定、胚培养、低温层积、赤霉素处理等方式对其休眠及萌发特性进行研究,结果表明：膜苞鸢尾种皮及胚乳均透水性良好,最适萌发温度为15/25℃,对光照要求不严;胚无休眠特性,种皮与珠孔端处胚乳对种子萌发有机械束缚;种皮与胚乳中分别含有水和醇溶性抑制物;低温层积能有效打破膜苞鸢尾种子休眠,沙藏40 d萌发效果最佳;NaOH处理浓度低于10%对种子萌发影响不大,但从10%开始随浓度增高萌发率明显降低,而不同浓度赤霉素处理对种子萌发无影响。     

温度对珠子参种胚生长发育的影响

[目的]了解温度对珠子参种胚生长发育的影响,掌握解除种子休眠的方法。[方法]采用不同温度条件下种子沙藏处理,定期取材,以解剖学的方法,对种胚的形态大小及发育情况进行观测。[结果]珠子参种胚属高低温型。在15℃下发育最好,约160 d即可达到满胚,后再转入5℃低温处理60 d即裂口。裂口种子10℃培养5 d就开始萌发。[结论]该研究为珠子参种子催芽育苗提供科学依据。     

Crop Residue Retention and Nutrient Management Practices on Stratification of Phosphorus and Soil Organic Carbon in the Soybean–Wheat System in Vertisols of Central India

The long-term crop residue retention coupled with external nutrient inputs are crucial for maintaining soil phosphorus (P) and soil organic carbon (SOC) in Vertisols of Central India. A study was conducted to evaluate the long-term effect of three wheat residue management practices (residue burning, incorporation, and surface retention) in combination with three supplementary nutrient inputs (SNI) [control, fertilizer, and farmyard manure (FYM)] on stratification of P and SOC in the soybean–wheat system in Vertisol. The wheat residue either incorporated or retained on the soil surface increased the availability of P and SOC content as compared to the common practices of residue burning. Residue retention or incorporation increased stratification of P and soil organic carbon over the residue burning. Irrespective of the nutrient treatments, greater stratification ratio of SOC and P were registered under wheat residue incorporation or retention compared to residue burning. It is evident from the study that wheat residue incorporation or retention plus addition of FYM could be an effective strategy for increasing the soil fertility in a soybean–wheat system of Vertisols of Central India.     

滇重楼种子内源激素含量与种胚长度和萌发的关系

[目的]通过研究滇重楼种子层积过程中不同阶段内源激素含量与种胚长度的动态变化情况来探讨种子休眠机理.[方法]应用酶联免疫吸附法测定不同阶段种子内激素含量.[结果]种子萌发过程中,脱落酸(ABA)含量由54.34 ng·g^-1·FW降至32.16 ng·g^-1·FW,赤霉素(GA)、玉米素核苷(ZR)显著升高,吲哚乙酸(IAA)含量波动较大,但整体呈逐渐升高趋势,随层积时间延长,未萌发种子中ABA含量持续降低,GA含量与GA/ABA值持续升高,仍显著低于已萌动种子中激素含量(p<0.05);种子在层积42天后,种胚开始膨胀,胚率快速增加;相关性分析结果,内源激素含量及比值与种胚生长呈显著相关(p<0.05),其中,GA/ABA值对种胚生长的影响最大.[结论]种子萌发过程中仅ABA含量降低不足以解除滇重楼种子休眠,同期GA含量升高和GA/ABA值达到某一阈值时能有效的解除滇重楼种子的休眠和促进胚的发育;种子在层积40天左右后,由于各项激素的综合作用,滇重楼种子由休眠状态逐步转变为破除休眠状态和萌发状态.     

林层划分方法综述

林层分层是热带林生态学最古老的概念之一, 但对林层分层的定义和测定方法的不同造成了林层分层是否存在及如何划分的争议.作为森林调查的因子, 对林层划分方法的研究具有测树学和群落学双重意义.文中从定性、定量和遥感3个方面综述林层划分的主要方法, 介绍剖面图的绘制、应用及特点, 描述TSTRAT和LMS划分方法的详细步骤, 并通过与FVS和MIDCL等划分方法的对比分析了这4种方法的特点.     

层积处理对野慈姑种子萌发的影响

探讨层积处理方法对野慈姑种子萌发的影响,以期为今后以野慈姑种子为萌发材料的相关试验研究与田间防除提供理论依据。试验结果表明：低温层积处理能够提高野慈姑种子的发芽率,处理5～10 d,种子能够发芽,但发芽率低;处理15 d时,种子发芽率大幅度提高,随后提高幅度减小;处理35 d后,种子逐渐达到低温层积处理的最高发芽水平,且与经过自然越冬的种子相比,发芽率无显著差异;处理60 d后种子发芽率不再提高;室温层积处理5～90 d野慈姑种子的发芽率均不高于4．00％,可见室温层积处理不能提高野慈姑种子的萌发率。