河西走廊绿洲区沙尘暴灾害的发生及其防治

甘肃省河西走廊绿洲地区是严重受荒漠化威胁的地区，而沙尘暴在该区的发生强烈地影响了当地人民的日常生活和社会经济的发展。尽管河西地区的沙尘暴和当地的自然因素息息相关，但人类的活动加剧了现代沙漠化的发展进程。恶劣的自然条件，如持续干旱、大风天气、丰富的沙源、植被稀疏、滥用水、土地以及植物资源等，导致了河西绿州区沙尘暴的频频发生。从沙尘暴的发生和发展的原因予以分析，最后提出了切实可行的防治措施。     

Plant community characteristics and their relationships with climate in the Hexi Corridor region of northwestern China

Species, coverage, density, appearance, important values and above ground biomass of desert plant communities in the Hexi Corridor region in northwestern China were investigated. Data on the meteorological factors at the investigation sites were collected. Their relationships were statistically analyzed. The results show that the composition of plant species and total density in the Hexi Corridor region are positively correlated with elevation and longitude, but negatively with latitude. The relation decreases from the southeast to the northwest in this region. In the desert regions with an accumulated temperature of >10°C greater than 3200°C, the shrubs, including semi-shrubs, occupy dominant positions in the communities. Their importance values reach 100. When the accumulated temperature is about 3000°C, the communities are often in some type of transition, either with herbage being the dominant species, with some semishrubs or shrubs as companion species, or the dominant species being semi-shrubs with some perennial herbage as companion species. In desert communities with an annual precipitation of over 110 mm, the main life forms of plants are semi-shrubs or perennial herbs. When precipitation is less than 110 mm, the main life forms of the vegetation are dwarf shrub or annual herbs. In the extreme arid regions with annual precipitation of around 50 mm in the northwestern part of the Hexi Corridor, barely some annual herbage come to life during the rainy season. Desert ecosystems consist of sparse vegetation with small biomass. They change with climate factors and are especially sensitive to precipitation, which is particularly important for their conservation. __________ Translated from Acta Botanica Boreali-Occidentalia Sinica, 2007, 27(5): 859–863 [译自: 西北植物学报]     

河西绿洲农田防护林主要模式研究

在对河西绿洲农田防护林调查研究的基础上,列出了12种防护林模式,并对各种模式的适宜条件、技术措施、存在问题进行了分析和评价。     

Effects of mutual shading of tree crowns on prediction of photosynthetic light-use efficiency in a coastal Douglas-fir forest

Gross primary production (GPP) is often expressed as the product of absorbed photosynthetically active radiation and the efficiency (epsilon) with which a plant community uses absorbed radiation in biomass production. Light-use efficiency is affected by environmental stresses, and varies diurnally and seasonally. Uncertainty about epsilon can be a serious limitation when modeling GPP. An important determinant of epsilon is the amount and type of solar radiation incident on a canopy, because an abundance of light can trigger a photo-protective reaction, diminishing GPP. The radiation regime in a forest canopy is determined by the predominant sky conditions and by mutual shading of tree crowns. Shading effects, producing shifts in the amount of incident direct and diffuse solar radiation, have been largely ignored, however, because they depend on forest structure and are difficult to measure. We describe a new approach for estimating changes in mutual canopy shading throughout the day and year based on a canopy structure model derived from light detection and ranging (LiDAR). Proportions of canopy shading were then combined with eddy covariance data to assess the explanatory power for variance in epsilon by regression tree analysis over half-hourly, daily and weekly time scales. The approach explained between 75 and 97% of variance in epsilon, representing an increase of between 5 and 16% compared with models driven solely by meteorological variables.     

河西走廊绿洲—荒漠过渡带生态恢复治理研究

绿洲—荒漠过渡带不仅影响着绿洲的物质循环和能量流动,同时还影响绿洲的稳定性和沙区群众的生存质量。结合遥感技术,对河西走廊绿洲—荒漠过渡带现状的研究结果显示:绿洲—荒漠过渡带地貌主要以流沙、固定沙地、半固定沙地为主;景观的破碎化程度高,各景观要素内部生境面积小,边缘长度短。采用由封沙育林育草带、植物活体沙障阻沙带、固沙林带和前沿防风阻沙带组成的"四带一体"综合模式治理后,在春季,绿洲—荒漠过渡区过境风速下降;生长季植物多样性增加,盖度提高,土壤含水量的变化不明显,治理区的生态环境得到了改善。     

河西走廊北部风沙区困难立地造林试验

张掖市甘州区兔儿坝滩是河西走廊北部生态屏障的重要地段,气候干旱,造林立地条件差,加之技术措施单一,导致多年造林成活率、保存率很低,为此,选择具有代表性的地段进行了河西走廊北部风沙区困难立地条件造林试验,结果表明,相同条件下,顶凌造林可提高造林成活率10～20个百分点,截干造林与全苗栽植相比,造林成活率提高10个百分点。因此,在干旱困难立地条件下造林,综合应用抗旱造林技术,不但可提高造林成活率,而且造林效果明显。     

N,P,and K characteristics of different age groups of temperate coniferous tree species in northwestern China

This study chose dominant tree species including Picea crassifolia,Pinus armandii and Pinus tabuliformis which are distributed in Qilian Mountains,Xiaolongshan Mountains,and Bailongjiang River.According to the different tree species,ages and components,we sampled leaves,branches,stems,and roots,and measured the contents of Nitrogen,Phosphorus,Potassium,along with soil fertility.The changes of N,P,and K contents in the different tree species were studied,and the relationship between nutrient content and environmental factors was analyzed.The results indicated that the content of P in all three species was the lowest(0.039–0.28 g kg~(-1)),while N content was the highest(0.095–1.72 g kg~(-1)).As the terminal organ of nutrient transport,the nutrient content of leaves was the highest.P.armandii(0.45 g kg~(-1)) had a higher nutrient concentration than P.tabulaeformis(0.19 g kg~(-1)) and P.crassifolia(0.29 g kg~(-1)).The nutrient content of each species was highest in a young forest,but lowest in a mature forest.The nutrient content of all three tree species was significantly affected by soil nutrient content,and negatively correlated with available soil nutrients.     

甘肃河西走廊盐碱地改造利用技术探讨

本文通过调查分析和试验研究,就甘肃省河西地区盐碱地改良的主要措施进行分析,指出了存在的问题,并提出了河西地区盐碱地改造利用的基本思路。     

Development and validation of a simple approach to modelling tree shading in agroforestry systems

There have been a number of models developed which attempt to predict the shading patterns beneath individual tree or forest canopies. We describe a computer-based model which is able to estimate shading patterns through a discontinuous canopy of pruned trees. The model is designed to assist in the layout and management of agroforestry systems with widely spaced trees. The model was tested against data collected from a seven-year-old agroforestry system involving radiata pine, located near Canberra, Australia. The model was shown to slightly but consistently underestimate light penetration at ground level beneath the trees. However, the extent of bias (0.7% to 5%) was so small as to be of little significance in practice.     

杏与药复合种植模式对杏幼树生长的影响

为了提高仁用杏果园的经济效益,将仁用杏与四种中药材进行复合种植,然后对仁用杏幼树的生长和生育指标进行了观测与分析。结果表明:同一中药材品种对仁用杏品种"超仁"、"龙王帽"的生长胁迫效应弱,对"超仁"、"一窝蜂"生育指标的降低幅度影响较小;而对仁用杏品种"一窝蜂"、"优一"的生长胁迫效应较强,对"龙王帽"、"优一"生长指标的降低幅度影响较大。仁用杏与中药材的复合种植组合应选择生长势较强的仁用杏品种和植株矮小的中药材品种进行配置,才能保证仁用杏植株的生长发育和优质高产。     

河西走廊肃北地区中亚紫菀木-裸果木荒漠群落特征

中亚紫菀木(Asterothamnus centrali-asiaticus)为半灌木超旱生植物,为亚洲中部特有种,广泛分布于亚洲中部荒漠区,但形成群落的较少。在我国主要分布于新疆、甘肃、宁夏、青海和内蒙古的荒漠地区(中国科学院植物研究所,1985;中国科学院中国植物志编辑委员会,1985;中国科学院兰州沙漠研究所,1992),喜生于疏松的砂砾质冲积扇和洪积土壤上。常沿干河床和流水线形成群落,也生于石质丘陵和山前洪积坡地上(中国饲用植物编辑委员会,     

Effects of organic and mineral fertilizer inputs on maize yield and soil chemical properties in a maize cropping system in Meru South District, Kenya

Soil nutrient depletion as a result of continuous cultivation of soils without adequate addition of external inputs is a major challenge in the highlands of Kenya. An experiment was set up in Meru South District, Kenya in 2000 to investigate the effects of different soil-incorporated organic (manure, Tithonia diversifolia, Calliandra calothyrsus, Leucaena leucocephala) and mineral fertilizer inputs on maize yield, and soil chemical properties over seven seasons. On average, tithonia treatments (with or without half recommended rate of mineral fertilizer) gave the highest grain yield (5.5 and 5.4 Mg ha⁻¹ respectively) while the control treatment gave the lowest yield (1.5 Mg ha⁻¹). After 2 years of trial implementation, total soil carbon and nitrogen contents were improved with the application of organic residues, and manure in particular improved soil calcium content. Results of the economic analysis indicated that on average across the seven seasons, tithonia with half recommended rate of mineral fertilizer treatment recorded the highest net benefit (USD 787 ha⁻¹) while the control recorded the lowest (USD 272 ha⁻¹). However, returns to labor or benefit-cost ratios were in most cases not significantly improved when organic materials were used.     

Effects of understorey vegetation on tree establishment and growth in a silvopastoral system in northern Greece

The interaction between understorey plants and trees in a young silvopastoral system was studied in a sub-humid Mediterranean environment with cold winters in northern Greece. The experimental design was a split-split plot with three replications and included: three understorey treatments (grass, legume and control), two tree species (Acer pseudoplatanus and Pinus sylvestris) and two spacings (2.5×2.5 m and 3.5×3.5 m). The competition between herbaceous plants and trees resulted in significant differentiation in tree growth while their spacing did not produce any significant differences. The influence of trees on herbage yield either by plant species or spacing was not significant. During the early stages of establishment, a significant positive correlation was observed between sycamore growth and soil moisture, leaf weight, leaf area and leaf number as well as nitrogen and potassium concentration in leaves. Six years after planting the height increase of the sycamore trees was largest in the control treatment (415%), lowest in the grass treatment (134%) and intermediate (192%) in the legume treatment. Much higher was the increase obtained for the diameter, 161%, 207% and 536% respectively for the grass, legume and control treatments. The Scots pine trees grew faster than sycamore over the course of the experiment. Height increased by 397%, 351% and 400% and diameter by 518%, 443% and 683% respectively for the grass, legume and control treatments. This revised version was published online in June 2006 with corrections to the Cover Date.     

河西生态林业建设成就、问题及对策

论述了生态林及林业可持续发展的概念，总结了甘肃河西生态林业40多年建设成就，针对河生态林业可持续发展中所存在的问题，提出了生态林业可持续发展的对策。     

Estimation of net gain of soil carbon in a nitrogen-fixing tree and crop intercropping system in sub-Saharan Africa: results from re-examining a study

Nitrogen (N)-fixing tree and crop intercropping systems can be a sustainable agricultural practice in sub-Saharan Africa and can also contribute to resolving climate change through enhancing soil carbon (C) sequestration. A study conducted by Makumba et al. (Agric Ecosyst Environ 118:237?C243, 2007) on the N-fixing tree gliricidia and maize intercropping system in southern Malawi provides a rare dataset of both sequestered soil C and C loss as soil carbon dioxide (CO₂) emissions. However, no soil C gain and loss estimates were made so the study failed to show the net gain of soil C. Also absent from this study was potential benefit or negative impact related to the other greenhouse gas, nitrous oxide (N₂O) and methane (CH₄) emissions from the intercropping system. Using the data provided in Makumba et al. (Agric Ecosyst Environ 118:237?C243, 2007) a C loss as soil CO₂ emissions (51.2?±?0.4?Mg?C?ha^?1) was estimated, amounting to 67.4% of the sequestered soil C (76?±?8.6?Mg?C?ha^?1 in 0?C2?m soil depth) for the first 7?years in the intercropping system. An annual net gain of soil C of 3.5?Mg?C?ha^?1?year^?1 was estimated from soil C sequestered and lost. Inclusion of the potential for N₂O mitigation [0.12?C1.97?kg?N₂O?CN?ha^?1?year^?1, 0.036?C0.59?Mg CO₂ equivalents (eq.) ha^?1?year^?1] within this intercropping system mitigation as CO₂ eq. basis was estimated to be 3.5?C4.1?Mg CO₂ eq.?ha^?1?year^?1. These results suggest that reducing N₂O emission can significantly increase the overall mitigation benefit from the intercropping system. However, significant uncertainties are associated with estimating the effect of intercropping on soil N₂O and CH₄ emissions. These results stress the importance of including consideration of quantifying soil CO₂, N₂O and CH₄ emissions when quantifying the C sequestration potential in intercropping system.     

Traditional tree crop based agroforestry in coffee producing areas of Harerge,Eastern Ethiopia

A preliminary survey of seven coffee producing Awrajas (Provinces) in eastern Ethiopia revealed that there is a traditional tree crop based agroforestry system being practised by the farmers. Coffee (C. arabica) was found to grow under the shade of several trees, 16 species, usually intercropped by one or several, a total of 15, important grain, fruit, vegetable, stimulant, oil-seed and spice crops. The majority of the trees, 69%, is leguminous and Ficus spp. The system is characterized by the integration of crops, livestock and sometimes apiculture. Recommendations are made for future studies.     

Effects of windbreaks on airflow, microclimates and crop yields

The mechanisms by which a porous windbreak modifies airflow, microclimates and hence crop yields are addressed, based upon recent wind tunnel experiments, field observations and numerical modelling. This paper is thus an update to the excellent reviews in Brandle (1988). It shows how a turbulent mixing layer initiated at the top of the windbreak dominates the airflow behind a windbreak. This mixing layer spreads vertically as it moves downwind, growing at a rate determined by the turbulence in the approach flow and the windbreak's ‘permeability’. The roughness of the terrain and land-cover upwind, windbreak height and porosity are thus the main controls on the amount and extent of shelter provided by a windbreak. The changes in temperature, humidity, heat and evaporation fluxes given these changes in turbulence are then described. Based on the turbulent mixing layer model, the highly sheltered ‘quiet zone’ will be typically warmer and more humid while further downwind in the ‘wake zone’, cooler and drier conditions would be expected. The careful experimental studies needed to verify these theoretical predictions have not yet been published. Shade is also shown to modify the heating in the quiet zone and, depending on the orientation of the windbreak, can offset the warming in the quiet zone. Lastly, the mechanisms affecting plant productivity are described in light of these airflow and microclimate changes. A major effect of a windbreak is to reduce the incidence of low frequency, high magnitude damage events such as sandblasting or lodging. Microclimate effects, however, do not always improve productivity. For example, while shelter may improve water-use efficiency in irrigated crops by increasing yields and reducing water-use, this may not be the case in dryland agriculture. This revised version was published online in June 2006 with corrections to the Cover Date.     

不同封育年限对河西走廊中部荒漠植被群落生态位的研究

选取河西走廊中部封育3、5、8、12、13、14年和未封育的荒漠植被,采用样带结合样方法进行野外植被调查,运用重要值、Levins生态位宽度指数和Pianka生态位重叠指数进行研究,分析了荒漠植被对资源的利用情况,揭示不同封育年限荒漠植被群落中种群生态位格局。结果表明,随着封育年限的延长和群落的演替,物种丰富度指数先增高后降低;物种均匀度指数和多样性指数呈先增高后降低再增高的变化趋势;物种重要值呈先降低再增高又降低的变化趋势。生态位宽度大的主要集中在盐生草、驼蹄瓣、刺沙蓬、苔草、沙蒿、画眉草、锋芒草、羊茅、红砂、青蒿等,说明这些植物适应环境能力强,能够充分利用环境资源,而且在群落中处于优势地位。     

遮阴处理对金蒲桃生长量及光合参数的影响

以2 a生金蒲桃(Xanthostemon chrysanthus)幼苗为材料,研究了全光照,50%遮阴,70%遮阴,90%遮阴4种遮阴处理对金蒲桃生长特性、生物量分配、光合生理变化的影响,结果表明:与自然光全处理对比,遮光极显著(P<0.01)地抑制了金蒲桃幼苗生物量的积累,遮光处理组叶片数量减少,叶生物量比下降,茎生物量比增加;光补偿点、光饱和点、暗呼吸速率和最大光合速率降低,光能利用效率低于全光照叶,强光下遮阴叶的净光合速率保持稳定.上述结果说明:遮阴处理后,金蒲桃在生长特性、生物量分配和光合参数上表现出对遮阴弱光的适应,表明金蒲桃是一种能广泛应用于各种光照条件的优良景观树种.     

Biomass production of tree fallows and their residual effect on maize in Zimbabwe

The rotation of maize (Zea mays) with fast-growing, N₂-fixing trees (improved fallows) can increase soil fertility and crop yields on N-deficient soils. There is little predictive understanding on the magnitude and duration of residual effects of improved fallows on maize yield. Our objectives were to determine the effect of fallow species and duration on biomass production and to relate biomass produced during the fallow to residual effects on maize. The study was conducted on an N-deficient, sandy loam (Alfisol) under unimodal rainfall conditions in Zimbabwe. Three fallow species — Acacia angustissima, pigeonpea (Cajanus cajan), and Sesbania sesban — of one-, two-, and three-year duration were followed by three seasons of maize. Pigeonpea and acacia produced more fallow biomass than sesbania. The regrowth of acacia during post-fallow maize cropping provided an annual input of biomass to maize. Grain yields for the first unfertilized maize crop after the fallows were higher following sesbania (mean = 4.2 Mg ha^–1) than acacia (mean = 2.6 Mg ha^–1). The increased yield of the first maize crop following sesbania was directly related to leaf biomass of sesbania at the end of the fallow. Nitrogen fertilizer did not increase yield of the first maize crop following one- and two-year sesbania fallows, but it increased yield following acacia fallows. Nitrogen fertilizer supplementation was not required for the first maize crop after sesbania, which produced high-quality biomass. For acacia, which produced low-quality biomass and regrew after cutting, N fertilizer increased yield of the first post-fallow maize crop, but it had little benefit on yield of the third post-fallow maize crop.This revised version was published online in November 2005 with corrections to the Cover Date.