红树植物化感作用对中肋骨条藻生长的影响

到目前为此,尚未见红树林区发生赤潮的报道:红树林不发生或极少发生赤潮的原因尚未完全清楚.红树林对污水具有净化功能,同时对其它植物存在化感作用.比较了几种红树植物粉对中肋骨条藻生长的效应,研究了红树粉及其水浸液、红树根系分泌物(无土栽培营养液)对中肋骨条藻生长的影响.结果表明:红树粉、红树粉水浸液、红树根系分泌物对中肋骨条藻生长均有明显的抑制作用:红树植物对中肋骨条藻生长存在化感作用,化感作用的强弱与红树总酚的含量不成正比,可能存在其它化感物质同时起作用.提示某些红树植物中存在抑藻物质,并能分泌到植物体外(主要通过根分泌),抑制赤潮藻类大量繁殖,对赤潮有一定的防治作用.     

同安区红树林调查及其管护对策

红树林生态系统是世界高生产力的生态系统之一,在维持海湾河口生态系统的平衡、和谐中起着特殊的作用。通过对1997年同安区人工种植红树林林区的现状调查,分析影响同安区红树林造林和保护的主要因素,并探讨利用雄厚的资源规划红树林种植和制定保护对策。     

具有活性的红树林真菌的多样性研究进展——优势菌为子囊菌和半知菌

红树林作为一种特殊的植物群落具有丰富的真菌资源,红树林真菌是具有特殊结构的生物活性物质的重要来源,相关研究近来倍受关注。本文列举出近年来产生次级代谢产物的具有活性的红树林真菌,分析后发现,具有活性的红树林真菌主要以子囊菌和半知菌为优势菌,这与绝大多数具有活性的海洋真菌主要以子囊菌亚门和半知菌亚门为多数的分布情况是一致的。     

我国超级稻根系特性及根际生态研究现状与趋势

以超级稻为代表的一批超高产水稻研发成功使水稻单产获得大幅度提高。较大的根系生物量、根重密度、根长、根长密度和根直径,根系偏向纵深分布且土壤深层根系生物量增大是超级稻根系生物学主要特征;高的单株根系氧化力、总吸收表面积、活跃吸收表面积、根系细胞分裂素(玉米素与玉米素核苷)含量是超级稻扩库增产的重要根系生理基础。生产中的施肥管理、水分管理、种植方式和根际土壤生态环境pH、氧、微生物、氮素形态等均可显著影响水稻根系的生长发育。通过适当的技术措施调控水稻根际生态环境向有利于水稻生长生理需求方向发展,以促进水稻根系健壮生长,实现水稻增产。水稻高产群体根系构型的形成与根际土壤生态因子匹配原理与调控,高产水稻地下根系、根际生态因子与地上群体的互作机制与调控路径,水稻根系定量化等方面是今后水稻根系深入研究的主要方向。     

推进瓯海生态区建设的若干思考

林业生态是陆地生态系统的主体，加快林业生态建设是加强生态建设，维护生态安全，推进经济社会可持续发展的重要基础。温家宝总理曾对林业在生态环境中的地位和作用做了深刻阐述：林业是生态建设最根本、最长期的措施。在可持续发展中，应该赋予林业以重要地位。2001年以来，瓯海区提出建设生态区的目标，按照“一要保护、二要发展”的方针，根据不同生态区位、自然经济条件与受益对象，全面实施生态公益林建设，努力改善生态环境，有力推进我区经济社会可持续发展和农业现代化建设。     

红树林区大型底栖动物研究进展

综述了近年来国内外红树林区大型底栖动物的研究进展。目前,红树林区大型底栖动物研究主要集中在物种多样性、影响因子、与其他生物的关系、次级生产力和污染生态学等方面。同时提出今后还应该更深入地进行红树林区大型底栖动物的多样性、红树林恢复过程中大型底栖动物的群落特征,并应用大型底栖动物对红树林生态系统进行监测和评价。     

再生稻根系研究进展与展望

综述了再生稻根系的组成与作用,再生稻根系机能与腋芽再生力、再生稻根系特性与稻谷产量之间的相关性,以及水分管理和耕作措施、施肥、植物生长调节剂等农艺措施对再生稻根系的调控等。同时对再生稻根系的研究方向进行了展望。     

水稻理想株型的研究进展

介绍了理想株型的涵义及发展历史，并从茎、叶片、穗、根系等4个方面，对水稻理想株型的研究进展进行了综述，提出了理想株型必须适应当地生产实际和生态条件、建立生态适应理想株型育种指标数学模拟体系等未来水稻理想株型研究的6个方向。     

秋茄红树林北移引种造林技术

秋茄红树林适应七都岛的滩涂生长环境，它顺利的通过1999年的百年不遇的-4.0℃低温考验，仍能生长良好且自然开发结果，表明引种试种已获成功，经四年的引种造林已形成了一个秋茄红树林与本地潮间带动，植物共存地的相对复杂的生态系统，这对改善，丰富、美化七都岛的生态环境有重要意义。芦苇是影响秋茄红树林造林成活率和生长的重要因素，清理芦苇，平整高洼地，以提高秋茄红树林造林成效，秋茄红树林北移到七都岛潮间土含盐量仅0.08%的滩涂上生长，表明对环境的盐度适应性进一步拓宽。     

文昌市红树林湿地资源现状及保护恢复建议

[目的]为掌握海南省文昌市红树林湿地资源现状,加强红树林湿地资源保护和恢复提供对策建议。[方法]以文昌市沿海乡镇分布的红树林湿地资源为调查对象进行调查研究。[结果]文昌市现有红树林湿地资源面积1 411.426 8 hm2,其中有林地（全部为天然林）占89.10%,未成林造林地占10.90%;红树林以文城镇分布最多（44.05%）;全市共分布红树植物16科35种,占全国37种红树种类的94.59%,以海莲（Bruguiera sexangula）(40.73%)、榄李（Lumnitzera racemosa）(21.89%)、红树（Rhizophora apiculata）(11.80%)、红海兰（Rhizophora stylosa）(10.82%)等树种为主。[结论 ]文昌市红树林湿地资源丰富,建议加大红树林造林规模,促进红树林保护和恢复。     

海南省生态盈亏及其空间结构研究

以生态足迹计算方法和泰尔指数等区域差距计算方法为模型工具,对海南的生态盈亏及其空间结构进行了系统研究。结果表明：海南省总量生态盈亏(ED)为2 357 083 hm2。在各项生态生产性土地中,盈亏较高的是总量水域、总量林地和总量耕地生态盈亏,较低的是总量草地、总量建设用地和总量化石能源用地生态盈亏。在18个市县中,总量耕地生态盈亏最高的市县是海口市,最低的是临高县。海南省人均生态盈亏为0.267 983 hm2。其中,人均水域、林地和耕地生态盈亏较高,人均草地、建设用地和化石能源用地生态盈亏较低。在18个     

Root Development,Water Uptake,and Shoot Dry Matter Production under Water Deficit Conditions in Two CSSLs of Rice: Functional Roles of Root Plasticity

Abstract

Root traits that can contribute to drought resistance have not been clearly indentified. We examined the role of root system development in enhancing water uptake and contribution to dry matter production by using the root box-pinboard method, with which quantitative assessment of root system development and the water uptake of root are possible. Chromosome segment substitution lines CSSL45 and CSSL50, and the recurrent parent Nipponbare were grown under continuously waterlogged conditions (control), and various intensities of water deficit in root boxes. There was no significant difference among the genotypes in shoot growth and root development, while CSSL45 and CSSL50 showed greater shoot dry weight than Nipponbare under water deficit conditions. This was due to their abilities to promote root system development as compared with Nipponbare, which facilitated greater water extraction than Nipponbare, especially under the mild water deficit condition of 20–25% w/w soil moisture contents. Furthermore, the increased root length density did not exceed the estimated critical value for water uptake, which indicates that plastic root system development was functionally effective and efficient for the enhancement of water uptake under mild water deficit conditions.     

依托资源优势 发展坡地苎麻 防治水土流失

本文介绍了我国水土流失状况和坡地苎麻防治水土流失的良好效果;从苎麻根系发达、覆盖度高、抗逆性强等方面阐明了苎麻保持水土的原因,并从成本低、见效快、缓解天然纤维与粮争地的矛盾、比较效益明显等方面分析了利用苎麻保持水土的优势。     

An empirical model for root water uptake

Soil water availability estimation is critical for assessing crop development and performance. During periods of soil water deficits, the capability of crop roots to extract soil water depends on the distribution and depth of its root system. Most water uptake models assume a relationship between root water extraction and root length density (RLD). However, models using RLD are difficult to test and several researchers have questioned the various proposed relationships between RLD and water uptake. A simplified water uptake model that does not use RLD was developed, but as an alternative, uses generalizations from measured soil water content changes to predict root water uptake. The daily incrementing model estimates a maximum water uptake rate by roots limited by soil water content that declines exponentially with the soil water content above the lower limit (LL) i.e., the remaining available soil water. The model assumes that: (i) the roots at a given layer have reached a minimum threshold of root density to extract water at a maximum rate; (ii) the transpiration demand is greater than the total root water uptake; and (iii) the water content at LL can be accurately measured or estimated. A critical constant (K) in the exponential model, representing the fraction of extractable water in a soil layer that can be taken up in 1 day, was found to be 0.096 for several species (cotton, maize, pearl millet, grain sorghum, soybean, sunflower and wheat), and different soil conditions. Values of K smaller than 0.096 were likely caused by root clumping in highly structured (cracking) or compacted soils, where root density was low in deeper soil layers when further downward root growth practically ceased, or by peanut whose K values was 0.064. This new empirical model should help to overcome several of the limitations of current models that rely on the use of measured or predicted RLD.     

Factors determining the leaching of nitrogen from soil,including some aspects of maintenance of water quality

N leaching from the topsoil, which occurs both by vertical percolation and runoff, is becoming increasingly important, not only from the point of view of crop production but also in the maintenance of water quality. N runoff from sloping fields has not yet been investigated extensively, but lysimeter studies have provided us with comprehensive data on vertical percolation of this nutrient. Numerous investigations throughout Europe have determined the most important factors concerned with N leaching from the topsoil and their relationship to water quality. The results may be summarized as follows: The amount and distribution of rainfall have a considerable effect on translocation of N from the topsoil. To exactly what extent is determined by the amount of water leached, which in turn depends to a large degree on the growth of the plant. Therefore the vegetative cover, as a result of its water utilization (mainly by transpiration) and its nutrient uptake, is often the most important factor in N leaching. This is borne out by the fact that by far the greatest leaching occurs in uncropped land (fallow) and during the part of the year where little growth occurs. Under crops with a limited root system and low transpiration, such as vines, leaching will also be higher than under a profuse plant cover (e.g. grassland). The main effect of the soil itself depends on its own N reserves and their mineralization rate. The amount of naturally occurring N in a mineral soil can vary between 600 and 12,000 kg/ha. Of this, approximately 10 – 250 kg/ha is given off anually under European climatic conditions. Thus as well as the factors already mentioned, the soil's N reserves also play an important part in the extent of N leaching. The vast majority of lysimeter studies carried out in Europe prove that the addition of N in mineral fertilizers has comparatively little influence on the amount of N leached out. An important point about N fertilizers is that they are applied when needed by the plant, which of course cannot occur in nature with the N from mineralization of the soil reserves. According to the data on hand, less than 5% of the N added in the form of mineral fertilizers will be leached out. Although excessive rates of N in lysimeter trials led to increased translocation into the subsoil, it was also proved that as a result of increased plant growth, N leaching losses were lower in a plot fertilized with N than in the PK control. Since N is leached out almost exclusively in the form of nitrate, and since the ammonium added as fertilizer is converted relatively quickly to nitrate, there is little difference in the leaching losses following application of the various types of N used today. The time of application, however, can be a determining factor. Gaseous N losses, in particular as a result of denitrification, can also affect N leaching indirectly. Discussion of N leaching leads inevitably to the question of water quality maintenance and what part N leached from soil plays in the eutrophication of surface waters and the nitrate content of ground water. The effect of agricultural land on the nitrate content of ground water depends on the cropping system: Vines, for instance, do not have a very extensive root system, and there are high leaching losses from the soil of vineyards. Under permanent grassland, on the other hand, the lowest losses have been recorded. In crops with a limited root system it is theoretically impossible to avoid an increase in the nitrate level of the ground water following high N application rates. This is however only a theory, and has not yet been fully investigated. In relation to agriculture as a whole these cases are to be regarded as exceptions, and they could possibly be improved by new agricultural techniques. As far as eutrophication is concerned, N leaching and the factors that affect it are of minor importance, since nitrogen, in contrast to phosphate, is already present in surface water at a concentration high enough to cause eutrophication. To sum up, it may be said that high rates of N are applied in intensive agriculture, but they do not usually lead to an increased N content in ground water and surface water. The reason for this is that the additional N promotes plant growth, which results in a greater nutrient uptake, and rationalization of agricultural methods on economic grounds ensures an adequate utilization of nutrients by applying rates commensurate with and timed according to the crop's need.     

Effects of rice-water chestnut intercropping on rice sheath blight and rice blast diseases

Both sheath blight and blast are important rice diseases worldwide. The exploration of environmentally sound practices to control these diseases will help to reduce fungicide application. Effects of rice (Oryza sativa) intercropping with water chestnut (Eleocharis dulcis) on rice sheath blight and rice blast disease as well as the extracts of different plant parts and root exudates from water chestnut on pathogens of rice sheath blight (Rhizoctonia solani) and rice blast disease (Magnaporthe oryzae) were investigated using pot experiments and bioassay tests. The results from pot tests showed that rice-water chestnut intercropping system suppressed sheath blight and blast and improved land equivalent ratio (LER). The results from bioassay tests indicated that extracts and root exudates from water chestnut had significant effects to inhibit the expansion of these pathogens. The scales of these inhibitions were time and concentration dependent. The antifungal activities of the extracts from aboveground parts and pulp of water chestnut were significantly higher than the extracts from other parts and root exudates. The water extracts of aboveground parts showed the highest antifungal activity on both pathogens according to EC₅₀ values. The antifungal activities of the same extracts from water chestnut on R. solani were significantly higher than on M. oryzae. The result suggests that water chestnut possesses bioactive substances to suppress rice sheath blight disease and rice blast disease. The rice-water chestnut intercropping system can be used as an environment-friendly method for diseases control in rice field.     

Genetic Opportunities to Improve Cereal Root Systems for Dryland Agriculture

Abstract

Understanding the major limitations to root growth is very important if we are to maximize water and nutrient use and increase yields. Limitations may be insufficient rooting depth, root diseases, nutrient deficiencies, toxicities and soil hardness. An understanding of these limitations will lead to more precisely identifying traits for which to select and breed. Examples of successfully overcoming limiting factors to improve crop performance by breeding and selection are given for cereal cyst nematodes in wheat, soil acidity and salinity. The importance of altered crop management practices to reduce limitations is also stressed. These have resulted in a more effective and healthier root system, which results in more water use and greater yields. Opportunities to genetically increase the size of the root system in dryland systems where water and nutrients are not all used by the crop are given.     

茶柿复合茶园生态经济效益研究初报

通过对五年生茶柿复合茶园空间结构分布、根系分布、土壤含水量、产量与产值的调查,得出茶柿复合栽培可以形成明显的双层空间结构,根系吸收面呈立体分布,提高了土壤水分涵养能力,从而提高了经济效益。     

干旱胁迫对大麦幼苗根系的影响

为了解干旱胁迫对大麦幼苗根系生长的影响,采用盆栽称重控制土壤含水量的方法,测定了土壤含水量为田间持水量的85%、55%、45%和35%等4个处理下, 4个抗旱性不同的大麦品种的幼苗根系形态和根系吸收能力等相关指标。结果表明,随着土壤含水量的减少,大麦幼苗的最长种子根、根尖数、根组织含水量均呈下降趋势;根分支数和根冠比总体呈上升趋势;根鞘大小和根毛密度整体上呈先上升后下降的趋势;根系活力与根总吸收面积和根活性吸收面积之间存在一定的互补效应。抗旱性较强的大麦品种较抗旱性较弱的品种,在干旱胁迫下能够保持更庞大的根系、更大的根-土交互面和更高的根系吸收能力。幼苗根系形态可以作为大麦耐旱性的筛选指标。     

The Use of Saline Water in Agriculture in the Near East and North Africa Region: Present and Future

SUMMARY

Salinity is a major problem that negatively impacts agricultural activities in many regions in the world, and especially the Near East and North Africa region. Generally, salinity problems increase with increasing salt concentration in irrigation water. Crop growth reduction due to salinity is generally related to the osmotic potential of the root-zone soil solution. This will lead to certain phenological changes and substantial reduction in productivity. Salinity also affects the soil physical properties. Sewage treated wastewater is an alternative water source for irrigation. Using such wastewater will provide a new water resource to expand agricultural activities as well as reduce the environmental pollution. Each country in the region has a unique system of rules and regulations to protect the quality of water resources. Important aspects that should be taken into account when using wastewater for irrigation are discussed, including some information on the different irrigation systems used in the region, and the factors leading to success of using saline water for economic crop production. Information on the use of saline water or marginal saline soils for wheat production and improvement of irrigation systems, including old land irrigation systems, under Egyptian conditions is also presented. The regional experiences and the future prospects of using saline water for crop production that vary greatly among countries in the Near East and North Africa region are summarized. This article also presents information on special cultivation methods, such as protected agriculture and soilless culture that can help in alleviating the salinity effects. Finally, the article includes some examples on the inherited knowledge for saline agriculture that conveys the grower's experience in the Near East and North Africa region where several living examples for unique and sustainable cultivation system are still in operation. One of the most impressive cultivation techniques for bio-saline crop management in Egypt is the Edkawy production system.