左云县店湾镇春季不同植被条件下土壤含水量研究

为了研究左云县店湾镇春季不同植被条件下0—600 cm深度范围内土壤垂直剖面水分变化特征,分别对该区乔木（白榆和小叶杨）林地、灌木（柠条和沙棘）林地和草地5种不同植被条件下土壤水分进行了研究。结果表明:研究区不同植被条件下土壤剖面含水量变化规律不同。左云县矿区春季各土层平均含水量草地最高,柠条林地次之,白榆林地最少。其中草地各土层平均含水量比柠条林地高0.3%,比白榆林地高3.8%。该区各植被条件下土壤水分主要呈难效水状态。且各植被条件下土壤在200—400 cm深度范围内都存在干层,有轻度干层、中度干层和重度干层发育。该区水循环主要是地表水循环,地下水循环基本不存在,形成了土壤—植物—大气的水分循环模式,属于异常水分循环类型。     

黄土高原坡面带状植被土壤水分有效性的空间分异特征

对黄土高原柠条和山杏2种带状格局植物篱20cm土层处土壤水分有效性的空间分异及动态变化进行了分析。结果表明:(1)2种带状植物篱带内、带前、带间、带后土壤水分有效性均差异显著(P0.05)。柠条植物篱土壤水分有效性随距植被带距离的增加而提高,而山杏植物篱土壤水分有效性随距植被带距离的增加而降低。(2)土壤水分有效性分级比较表明,柠条植物篱带间土壤水分为中效水,带后、带前、带内均为难效水,而山杏植物篱带内土壤水分为易效水,带后和带间均为中效水。(3)在土壤持水性能方面,柠条植物篱最大持水量表现为带间(69.91%)、带内(62.54%)高于带后(60.31%)、带前(56.52%),而最小持水量为带间(53.20%)最高、带内(33.05%)最低。山杏植物篱带间土壤最大持水量、毛管持水量、最小持水量分别是带内的1.05,0.96,1.35倍。(4)在20—100cm土层内,柠条植物篱各部位土壤体积含水量除在40cm土层处差异不显著外,其他各土层均差异显著(P0.05)。在表层(20cm)表现为带内带后带前带间,随着土层深度的增加带内土壤体积含水量逐渐降低,带间土壤含水量逐渐增加。山杏植物篱各部位土壤体积含水量基本相同,且增减变化一致,土壤含水量不受植被带距离的影响。(5)在降水条件下,柠条植物篱各部位土壤水分有效性空间动态变化表现为带间带后带前带内,山杏植物篱各部位土壤水分有效性动态变化表现为带内带后带间。(6)柠条植物篱系统带内和带间在20—200cm土层内为干层;梯田在60—200cm土层内为干层;植被严重影响着土壤干层的厚度及分布;干层化程度表现为柠条植物篱带内带间梯田。在进行植被恢复重建时应考虑当地的降水变化、土壤理化性质、植被类型,选择适宜的植被类型,并合理设置种植密度,才能减少因土壤干层化引起的土壤水分亏缺对植被恢复重建的影响。     

黄土丘陵苜蓿与柠条深层土壤干化状况及根系与养分特征

[目的]探究宁夏南部黄土丘陵区雨养苜蓿及柠条地的深层根系与土壤水分和养分的协同关系，进而为宁南山区人工植被建设与管理以及生态环境高质量发展提供科学依据。[方法]采用野外调查与室内分析相结合的方法，对宁南黄土丘陵区人工种植18 a的紫花苜蓿地与20 a的柠条林地0—1 000 cm土层中土壤水分、根系垂直分布、土壤N,P含量变化进行了分析。[结果](1)苜蓿地和柠条林地土壤200 cm以下全剖面已经处于干化状态，其中苜蓿和柠条地土壤处于极度干燥化水平的土层分别为200—720 cm和360—720 cm, 0—1 000 cm深度范围土壤水分储量较相似地形的雨养农田分别少987.55,977.78 mm;(2)苜蓿和柠条根系主要集中在表层0—120 cm土层，该层根系占0—1 000 cm剖面总根干重的45.66%,57.54%,根长密度占44.45%,67.58%;(3)苜蓿和柠条土壤N,P养分分布规律与根系分布规律一致，表层0—120 cm范围内平均全N含量分别为0.53,0.58 g/kg,是0—1 000 cm土壤全N含量平均值的1.77倍和1.87倍，在0—120 cm范围内全...     

黄土高原典型植被条件下土壤剖面水、碳分布季节变化研究

采用土钻法对黄土高原柠条林地、苜蓿草地和撂荒草地0～300 cm土壤水分、有机碳的季节变化及二者相互关系进行了探讨,结果表明：(1)3种植被条件下0～100 cm土壤含水量存在显著季节变化,但该土层土壤含水量仅雨季后植被间差异显著;>100～200 cm和>200～300 cm土壤含水量季节变化程度不一致,但各季节植被间差异均显著;柠条林地和苜蓿草地100 cm以下土壤含水量明显低于撂荒草地,两者分别在100 cm和200 cm深度以下出现了严重土壤干燥化。(2)3种植被条件下0～300 cm土壤有机碳存储量均为雨季中最低、除柠条林地0～50 cm土层外雨季前最高,柠条林地季节变化较小,苜蓿草地和撂荒草地季节变化较大。(3)3种植被条件下土壤有机碳含量具有不同程度的表聚现象;0～50 cm土壤有机碳密度3种植被间差异均显著;>50～100 cm土壤有机碳密度柠条林地明显高于撂荒草地,两者与苜蓿草地的差异均不显著;>100～300 cm土壤有机碳密度3种植被间差异不显著。柠条和苜蓿的种植分别增加了100 cm和50 cm以上土壤有机碳密度,但导致深层土壤干燥化,不...     

黄土丘陵沟壑区不同退耕草地土壤水分研究

为了研究黄土丘陵沟壑区不同退耕方式、不同深度土壤水分含量的变化规律。以陕西省安塞县纸坊沟流域水平阶草地和自然草地两种退耕草地为研究对象,通过野外定位连续观测资料,研究了两种草地0—500 cm土层内的土壤含水量变化。结果表明:降水对土壤水分的影响比较明显,且水平阶退耕草地土壤含水量(13.38%)自然退耕草地(13.21%);水平阶退耕草地和自然退耕草地浅层土壤含水量的年内变化趋势基本相同;200 cm深度以下水平阶退耕草地普遍高于自然退耕草地;在不同生长周期土壤水分在不同深度具有明显差异,以生长期为例,0—100 cm深度平均土壤含水量自然退耕草地(12.46%)水平阶退耕草地(11.58%),100 cm深度处自然退耕草地(14.02%)水平阶退耕草地(14.44%);次降雨对不同深度土壤含水量的影响不同,对表层土壤含水量影响最大。研究结果表明:在退耕还草基础上应该适当采取一些水土保持措施来提高退耕地植被恢复的效果。     

荒漠草原区不同土地利用方式下土壤水分相对亏缺

以典型荒漠草原区(宁夏盐池县柳杨堡乡杨寨子村)作为研究对象,采用土壤水分相对亏缺指数(CSWDI)、样地土壤水分相对亏缺指数(PCSWDI)、土壤有效储水量(ESWS)、土壤水分相对亏缺量(DSWS)、变异系数(CV)5个指标来衡量旱地、天然草地、柠条林地3种土地利用方式下土壤水分的亏缺程度。研究结果表明:(1)旱地、天然草地、柠条林地的土壤储水量和土壤有效储水量与降雨量的变化趋势相同。且降雨对剖面土壤水分的影响程度随土层深度的增加而减弱。(2)土壤水分亏缺状况表现为旱地柠条林地天然草地。天然草地土壤水分不亏缺,旱地、柠条林地土壤水分呈亏缺状态。(3)天然草地土壤水分蓄积效应最强,土壤水分亏缺主要集中在表层。旱地土层越深土壤水分越亏缺土壤水分亏缺。柠条林地0-100cm土层土壤水分不亏缺,100-200cm土层土壤水分亏缺。(4)旱地、天然草地、柠条林地土壤水分剖面变化分别呈现波动型、增长型和稳定型。     

宁夏盐池不同草地类型的土壤水分平衡研究

以位于农牧交错地带盐池县的6种不同草地类型土壤含水量为研究对象,通过监测各种类型草地0—100cm土层质量含水量的动态变化情况,运用Surfer制图软件分析牧草生育期土壤水分的空间分布特征;利用土壤水分平衡方程和土壤分层贮水量公式计算不同草地0—100cm土层总贮水量变化情况,结合试验地生长季降水量变化,分析了不同草地类型土壤贮水量动态变化与蒸散量的变化规律,结果表明:降雨和植被类型是不同类型草地土壤水分动态变化的主要原因,沙丘土壤水分随降雨量变化较为明显;移栽柠条地土层剖面生育期水分变异系数最大,表明干旱时土壤失水较多,降雨充足时蓄水最多。因此应增加沙丘植被覆盖,对柠条、苜蓿、草地应适度进行放牧和刈割,控制植被生长,减少植被蒸腾蒸发,提高土壤水分固持能力,维持土壤水分的可持续发展。     

露天煤矿排土场不同植被土壤水分特征及其时间稳定性

选择晋陕蒙接壤区永利煤矿排土场沙打旺草地、紫花苜蓿草地、沙棘林地和原地貌草地土壤水分为对象,研究其蒸散、剖面分布、时间变化等特征,以期揭示土体重构及不同复垦植被模式对土壤水分及其时间稳定性影响。结果表明:排土场3种人工植被条件下土壤平均含水量同原地貌草地相比提高了50.7%~62.3%,另外,沙打旺复垦草地土壤含水量显著低于苜蓿复垦草地和沙棘复垦灌木林地(均降低了7.2%)。沙打旺和苜蓿会导致深层(120—260,120—220 cm)土壤水分亏缺,但有利于20—80 cm的土壤水分的保持;而沙棘易导致浅层(20—80 cm)土壤水分亏缺,但对深层(100—280 cm)土壤水分影响较小。上述结果说明,矿区排土场土体重构过程能够改善排土场土壤的水分条件,并且在进行植被重建的过程中,不同复垦植被对土壤水分的保持与利用形式有所不同,在本研究中,苜蓿和沙棘更有利于缓解土壤水分亏缺。     

黄土高原小流域土壤水分及全氮的垂直变异

为了研究黄土高原土壤中水分及全氮垂直分布及变异情况,对陕北神木县六道沟小流域中苜蓿地、荒草地、农地、柠条地以及油松地5种不同植被类型下0～800 cm土层中土壤含水率和土壤全氮进行了测定和分析。土壤含水率在垂直方向上呈现出干湿交替的层状分布。植被类型影响土壤水分含量的垂直剖面分布;各植被类型下相对高湿层和低湿层出现的深度不同;不同深度土层平均土壤含水率不同。农地及退耕荒草地土壤水分涵养较好,垂直方向上含水率变化较大;人工植被苜蓿、柠条消耗土壤水分较多,土壤含水率变化相对平缓;油松地平均土壤含水率及变化幅度居中。研究区域中,土壤全氮含量水平较低,表层发生陡降后,在20 cm以下土层中仍以很小的变幅降低,变化平缓。柠条地土壤全氮含量高于其他植被类型。     

晋北丘陵风沙区不同植被恢复模式的水土保持效应

通过对山西右玉贾家窑阳坡退耕还林约20年后的4种植被恢复模式(自然恢复草地、油松林、柠条灌丛和油松—柠条林)土壤水分、理化性质、径流量和侵蚀量的测定,探讨了不同植被恢复模式的水土保持效应。结果表明:(1)4种植被恢复模式0—100cm土层土壤平均含水量无显著差异,油松林和自然恢复草地的土壤容重高于油松—柠条林和柠条灌丛,土壤总孔隙度的变化趋势与容重相反;(2)4种植被恢复模式0—20cm土层土壤粒度组成、pH、有机质、铵态氮和速效磷无显著差异,硝态氮和速效钾差异明显(P0.05);(3)4种植被恢复模式径流量没有明显差异,但土壤侵蚀量自然恢复草地和油松林显著高于柠条灌丛和油松—柠条林(P0.05);(4)覆盖度相似条件下,根系密度、近地表植被盖度和枯枝落叶层厚度是影响林草植被水土保持效应的主要因素。     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Enhanced establishment and growth of giant cardon cactus in an eroded field in the Sonoran Desert using native legume trees as nurse plants aided by plant growth-promoting microorganisms and compost

To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.     

Karyotypic and genome size variation in Cajanus cajan (L.) Millsp. (pigeonpea) and some wild relatives

Detailed karyotypes and 4C DNA amounts have been studied in five cultivars of Cajanus cajan and 20 species belonging to Cajanus, Rhynchosia, Dunbaria, Flemingia and Paracalyx. C. cajan shows intraspecific variability and its karyotype is most similar to that of C. cajanifolius (sect. Cajanus) in the morphology and number of satellite chromosomes and the lack of any correlation between chromosome size within the complement and asymmetry. Karyotypes of C. lineatus and C. sericeus belonging to sect. Atylia are similar with respect to maximum r-index and the ratio of longest and shortest chromosomes in their respective complements. C. acutifolius (sect. Frutocosa) is distinct in having a very low ratio (1.44) between the longest and the shortest chromosomes, while in C. albicans, C. goensis, C. scarabaeoides (sect. Cantharospermum) there is no chromosome pair with r-index >2.0. C. mollis and C. volubilis (sect. Volubilis) show similarity with regard to ratio between the longest and the shortest chromosomes and a distinct chromosome pair with an arm ratio of 2.7 and C. platycarpus is distinct (sect. Rhynchosoides) in having the smallest ratio (1.36) between the longest and the shortest chromosomes. 4C DNA amounts in Cajanus and Rhynchosia vary between 3.28 pg to 11.69 pg and 4.92 pg to 11.13 pg respectively, while in Dunbaria, Flemingia and Paracalyx these vary between 4.70 and 7:06 pg. In the genus Cajanus karyotypic features and 4C DNA amounts agree with the sectional classification and bring out a close relationship between C. cajan and C. cajanifolius. This is supported by studies based on seed protein patterns, isozyme analysis, trypsin and chymotrypsin inhibitor patterns, RFLP and RAPD data and crossability relationships. A clear relation between DNA amount and abnormalities effecting the extent of pairing and recombination in interspecific hybrids shows the importance of this study in developing future breeding programme involving C. cajan and its wild relatives that are of potential value.     

Effect of some fungicide seed treatments on the survival of Bradyrhizobium japonicum and on the nodulation and yield of soybean [Glycine max. (L) Merr.]

Several commercial fungicide seed treatments were evaluated for their possible effect on the survival of Bradyrhizobium japonicum on seeds and on the nodulation and yield of soybeans in a greenhouse and a field experiment. quinolate Pro (carbendazim and oxine copper), Vitavax 200FF (carboxin and thiram), and Monceren (pencycuron) had a small effect or no effect on the survival of B. japonicum and on the nodulation and yield of soybeans. They can thus be considered compatible with soybean seed inoculation. Germipro UFB (carbendazim and iprodione), Apron 35J (metalaxyl), and Tachigaren (hymexazol) decreased B. japonicum survival and the nodulation and yield of soybeans and thus cannot be considered compatible with soybean seed inoculation.     

Einfluss der düngungsmethoden auf die entwicklung von zuckerrübenkrankheiten

Während neunjähriger (1994-2002) Untersuchungen in der Versuchsanstalt Ba?cyny (Fahlerde, Fall-Gleyboden, ausgebildet aus leichtem Lehmboden) wurde der Befall mit Krankheiten an der Zuckerrübe in Abhängigkeit von der Düngungsmethode bewertet. Folgende Methoden wurden angewendet: A - Mineraldünger, B - Stalldung und Mineraldünger, C - Stroh-, Gründung und Mineraldünger, D - Kompostdünger und Biopräparate (ökologische Düngung). Auf den Objekten A, B, C wurden bei konstanter Phosphor-Kalium-Düngung die Stickstoffgaben von 0 bis 180 kg.ha^?1 differenziert. Auf dem ökologischen Objekt D ohne Mineraldünger wurden statt Stickstoff die Biopräparate P₅₀₀ und P₅₀₁ verabreicht. Der geringste Befall von Krankheiten wurde an der Zuckerrübe auf jenem Objekt festgestellt, das mit Kompost und den Biopräparaten gedüngt worden war. Im Rahmen der konventionellen Düngungsmethoden wurde allgemein die höchste Intensität der Krankheiten an der mit Stroh, Gründung und Mineraldünger gedüngten Zuckerrübe beobachtet. Ausnahmen von dieser Regel bildete das Vorkommen von echtem Mehltau und Keimlingsfäule. Auf den Objekten A, B, C nahm die Intensität der Krankheiten mit der Steigerung der Stickstoffgabe zu. Auch die auf Objekt D verabreichten Biopräparate stimulierten die Entwicklung der Krankheiten. The effect of various fertilization methods on the diseases of sugar beet was estimated on the basis of nine-year studies (1994-2002) conducted in the Experimental Production Farm in Ba?cyny on loess-based, sedimentary-gley, light-clay soil. The following fertilization methods were applied: A - mineral fertilization, B - mineral and manure fertilization, C - straw, green manure and mineral fertilization, D - ecological compost and biodynamic preparations fertilization. In the objects A, B and C fertilized with phosphorus and potassium, various doses of nitrogen ranging from 0 to 180 kg/ha^?1 were used. In the ecological object D, where mineral fertilization was not used, biodynamic preparations P₅₀₀ and P₅₀₁ were applied instead of nitrogen. The lowest ratio of the diseases of sugar beet was observed in the object fertilized with the compost and biodynamic preparations. In view of the conventional fertilization methods, generally the highest incidence of diseases was noted in the sugar beet fertilized with straw, green manure and mineral fertilizers. The exception was the occurrence of powdery mildew and the black leg. In objects A, B and C the incidence of the diseases increased with the increase in nitrogen doses. The applied biodynamical preparations in the object D stimulated the development of diseases too.     

Prospects for control of Pythium damping-off of lettuce with Trichoderma,Gliocladium and Enterobacter spp.

Summary Damping-off of lettuce (Lactuca sativa) caused by Pythium ultimum was studied in pots containing a non-sterile potting mix in the glasshouse. Fifty P. ultimum sporangia g^-1 compost reduced the plant stand to 15% and shoot dry weight to 18%, but this reduction was totally prevented by applying Trichoderma harzianum at 2×10⁵ viable propagules g^-1 potting mix. Gliocladium virens and Enterobacter cloacae also alleviated the damping-off. E. cloacae did not adversely affect the action of the fungal antagonists. The co-existence of the bacterial and fungal antagonists was revealed on the root surface and inner surface of the testa by scanning electron microscopy, indicating the compatibility of the biocontrol agents.     

细菌、真菌及植物氮营养信号研究进展

氮素吸收代谢是所有生物生命活动的核心部分,因此,各种生物对氮的吸收与同化过程都有精细的调节。这种调节依赖于生物对体内氮素状况信号及体外（生长介质中）氮素信号的感受。过去几十年中,在细菌、真菌中已经对氮素营养信号有了较好的研究,而植物中则相对缓慢,但也有了一定的认识。本文重点比较细菌、真菌及植物中氮信号系统的组成,以期为进一步认识植物中的氮信号接受与转导系统提供启示。     

Aircraft operations near concentrations of birds in Antarctica: The development of practical guidelines

Aircraft operations have the potential to disturb and to impact negatively on bird life. A gradient of increasing behavioural response is evident in birds when exposed to increasing aircraft stimulus. The most major disturbance is likely to lead to impacts on the health, breeding performance and survival of individual birds, and perhaps bird colonies. A process of revision to policies on aircraft operations contained in management plans for a number of specially protected areas in Antarctica by the United Kingdom, accompanied by consultations made within the scientific community through the Scientific Committee on Antarctic Research (SCAR) and with operational interests through the Council of Managers of National Antarctic Programmes (COMNAP) resulted in new guidelines being adopted by the Antarctic Treaty Consultative Parties in June 2004. The principal recommendations of the guidelines are that bird colonies should not be overflown below 2000 ft (∼610 m) above ground level and landings within 1/2 nautical mile (∼930 m) of bird colonies should be avoided wherever possible. These guidelines are less stringent and less specific than those that were recommended by the SCAR specialist group on birds, and represent a compromise to accommodate operational needs. While the adoption of clear and consistent guidelines for the operation of aircraft in Antarctica is welcome in that this provides practical advice that is likely to reduce incidences of close aircraft/bird encounters, there remains insufficient knowledge of the interactions between aircraft and birds in Antarctica, and the consequent impacts on individual birds and on bird populations. It is important, therefore, that the guidelines adopted are considered interim, and should be kept under scrutiny with revisions made as new and improved research results appear.     

The abundance of heterocystous blue-green algae in rice soils and inocula used for application in rice fields

Summary Algal populations were quantified (as colony-forming units [CFU] per square centimetre) in 102 samples of rice soils from the Philippines, India, Malaysia and Portugal, and in 22 samples of soil-based inocula from four countries. Heterocystous blue-green algae (BGA) were present in all samples. Nostoc was the dominant genus in most samples, followed by Anabaena and Calothrix. In soils, heterocystous BGA occurred at densities ranging from 1.0 × 10² to 8.0 × 10⁶ CFU/cm² (median 6.4 × 10⁴) and comprised, on average, 9% of the total CFU of algae. Their abundance was positively correlated with the pH and the available P content of the soils. In soil-based inocula, heterocystous BGA occurred at densities ranging from 4.6 × 10⁴ to 2.8 × 10⁷ CFU/g dw (dry weight), comprising only a moderate fraction (average 13%) of the total algae. In most soils, the density of indigenous N₂-fixing BGA was usually higher than that attained by applying recommended rates of soil-based inoculum. Whereas research on the practical utilization of BGA has been mostly directed towards inoculation with foreign strains, our results suggest that attention should also be given to agricultural practices that enhance the growth of indigenous strains already adapted to local environmental conditions.Maître de Recherches ORSTOM (France), Visiting Scientist at IRRI