Genetic structure of a population of Ganoderma boninense on oil palm

Ganoderma boninense (the causal agent of basal stem rot of oil palm in Papua New Guinea) has a tetrapolar mating system with multiple alleles. Investigations into the population structure of G. boninense , using interfertility between isolates as a marker, revealed that the population on oil palm was comprised predominantly of genetically distinct individuals, although a number of isolates were found to share single mating alleles. No direct hereditary relationship was found between isolates on neighbouring or spatially separated diseased palms, indicating that outcrossing had probably occurred over several generations in the founder population prior to colonization of oil palm. In this study, a total of 81 A and 83 B mating type alleles (factors) were detected with 18 allelic repeats at the A locus and 17 at the B locus. Alleles appeared to be randomly dispersed throughout the population in each study block, although there was a significantly ( P  < 0·01) higher proportion of allelic repeats between estates separated by several kilometres compared to within estates. This is the first study on the population structure of this species and confirms that sexual reproduction is a significant component of the epidemiology of this disease.     

Landscape dynamics and equilibrium in areas of slash-and-burn agriculture with short and long fallow period (Bragantina region,NE Brazilian Amazon)

Fallow periods used in slash-and-burn agriculture in the Bragantinaregion, the oldest agricultural frontier in the Brazilian Amazon, are beingreduced. The objective of this study was to analyze the effects of a shortenedfallow period on the Bragantina landscape dynamics and equilibrium. Dynamicswere characterized by landscape structural changes, particularly in the spatialdistribution of secondary forests, and by transition matrix. Equilibrium wasdefined by temporal and spatial parameters, and by the increment ofagriculturalareas from 1985 to 1996, analyzed with 6 LANDSAT-TM images. I worked with 6areas of 250 ha each, 3 with short fallow periods (2–4years)and 3 with long fallow periods (about 10 years). Results showed that shortfallow period areas did not present an equilibrium situation. In these areas,developed secondary vegetation tended to disappear and agricultural areas werebeing expanded at an average rate of 3% per year. Landscape structure changespointed out that a reduction in fallow period was occurring in already shortfallow period areas. Long fallow period areas presented a shifting mosaicsteady-state condition, where punctual changes due to agricultural uses werecompensated by field abandonment rate. Both agricultural uses and fieldabandonment rates were lower in long fallow period areas when compared withshort ones. Comparisons with indigenous traditional cropping-fallow cyclesindicate that sustainable conditions could be maintained with 11 years offallowfor each cropping year, while shorter cycles would break down the system ifagricultural improvements are not implemented.This revised version was published online in May 2005 with corrections to the Cover Date.     

气候异常对青海湖环湖地区草地蝗虫灾害发生的影响

采用合成分析和相关分析方法研究了气候异常对青海湖环湖地区草地蝗虫灾害发生的影响。合成分析表明蝗虫灾害严重与当年气候状况关系密切。蝗灾等级与前一年7～8月平均气温、当年2～8月月平均气温、冬季降水量呈正相关 ,而与前一年7～9月降水量、10～12月气温、当年5～9月降水量呈负相关关系。这说明前一年和当年夏季温暖少雨、冬季多雪有利于蝗虫生长发育和越冬 ,会造成蝗灾 ,相反则不会发生     

施氮对苦豆子生物性状和生物量积累动态的响应

研究了不同氮肥水平(0、50、100、150、200 kg/hm2)对苦豆子Sophora alopecuraides生物性状和生物量积累动态的影响,旨在探索人工栽培苦豆子的施氮量,从而提高苦豆子栽培的生物产量.结果表明:施氮对其株高、单株茎数均有增加效果,增施氮肥对各时期的株高增加效果明显,特别是在7-8月,茎的生长速率明显高于对照,施氮肥对根直径的增加效应不显著;氮肥对单株根鲜质量和干质量增加效应显著,施用氮肥使茎叶鲜质量和干质量开始下降的时期推迟.100和150 kg/hm2施肥处理对生物量的增加幅度明显高于对照.     

卫星搭载不同紫花苜蓿品种的生物学特性反应(简报)

太空育种具有变异多、幅度大、高产、优质、早熟及抗病力强等特点,是集航天技术、生物技术、农业育种技术于一体的农业育种新途径。以不同时期株高为指标,对3个紫花苜蓿Medicago sativa品种卫星搭载效应进行研究。结果发现,对于中苜一号,幼苗期卫星搭载株高显著低于地面对照,分枝期和初花期则相反,搭载后株高显著增加;对于龙牧803,卫星搭载后幼苗期和分枝期的株高显著增加,初花期则表现为无显著差异;对于敖汉苜蓿,卫星搭载植株在3个时期的株高都显著高于对照;研究结果表明,卫星搭载的生物学效应因品种和时期而异,这可能是由不同紫花苜蓿品种间诱变敏感性的差异引起的。     

保护性耕作下陇东春玉米-冬小麦-夏大豆轮作系统土壤水分动态及水分利用效率

在黄土高原西部连续5年定位观测了4种耕作措施[传统耕作(T);传统耕作 秸秆覆盖(TS);免耕(NT)和免耕 秸秆覆盖(NTS)]下春玉米-冬小麦-夏大豆轮作系统中的水分动态及其水分利用效率,结果表明:土壤含水量受降水的影响较大,年内和年际的变率大,200 cm内土壤含水量在350～600 mm变动;土壤贮水量5-7月上旬因作物利用迅速下降,在雨季得到补充,到冬季缓慢下降;水保耕作措施对玉米Zeamnys、小麦Triticum aestivum和大豆Glycine max生育期200 cm土体耗水量影响不大,但秸秆覆盖能有效增加玉米-小麦-大豆轮作系统的水分利用效率;与传统耕作相比,免耕没有造成轮作系统的减产和水分利用效率的降低,免耕、秸秆覆盖可增加农民收入;在土地利用强度极高的玉米-小麦-大豆轮作系统,改大豆为利用营养体的豆科牧草,可提高系统的水分和光能利用率.     

多年生黑麦草生物滤清系统滤清效果和N素动态分析

采用设施条件下单层无纺织布盘培多年生黑麦草生物滤清系统来净化养鳖废水,分析了系统的滤清效果和多年生黑麦草处理期间地上部分、地下部分生物量的变化,以及水体、植株间 N、P 等的动态变化,结果表明:该生物滤清系统对养鳖富营养化废水有很好的去除效果,处理期间CODcr去除率为94.09%,SS去除率为89.19%,NH4 -N去除率为92.15%,TN去除率为55.83%,TP的去除率为60.98%;其中植株的吸收占总氮去除的88.45%、总磷去除的85.03%,植株地上部分的积累大于地下部分的积累;系统间歇供水的方式有利于植株氨氮的吸收同化和水体氨态氮向硝态氮的转化,系统对以氨氮为主的富营养化废水有很好的滤清效果,研究结果为利用陆生植物治理富营养化水域提供了新的途径.     

Projecting future fish supplies using stock dynamics and demand

Supply–demand models, which are commonly used in food policy analysis, have been recently applied to generate projections of future fish supplies. However, these models routinely ignore stock dynamics; hence, threats to sustainability due to declining fish stocks are addressed, at best, by exogenous changes in resource productivity. Such a device is ad hoc, as it is unclear whether the assumed shifts are consistent with known patterns of population adjustment. On the other hand, bioeconomic models incorporate stock dynamics, but typically omit price adjustment arising from the interaction of demand and supply. An applied supply–demand model with stock dynamics combines the strengths of both approaches. However, data problems constrain the formulation of such a model. Instead, this study presents a prototype bioeconomic supply–demand model. Simulations show trends in fish supply that fail to appear in either supply–demand or bioeconomic models. Secular demand growth causes initial production growth, followed by stagnation, and then persistent decline. Moreover, under constant pressure from rising demand, capture production fails to recover completely from adverse population shock (such as may be induced by climate change). The prototype model highlights the potential usefulness of an applied bioeconomic supply–demand model for food policy and fisheries management, and provides a template for future work.     

Movement and behaviour of large southern bluefin tuna (Thunnus maccoyii) in the Australian region determined using pop‐up satellite archival tags

Pop‐up satellite archival tags (PSATs) were deployed on 52 large (156–200 cm length to caudal fork) southern bluefin tuna (Thunnus maccoyii) in the western Tasman Sea during the austral winters of 2001–2005. Southern bluefin tuna (SBT) were resident in the Tasman Sea for up to 6 months with movements away from the tagging area occurring at highly variable rates. The data indicated a general tendency for SBT to move south from the tagging area in the Western Tasman Sea. Four individuals migrated west along the southern continental margin of Australia and into the Indian Ocean. Three individuals moved east into the central Tasman Sea, with one individual reaching New Zealand. We also describe the first observed migration of an SBT from the Tasman Sea to the Indian Ocean spawning grounds south of Indonesia. Individuals spent most of their time relatively close to the Australian coast, with an estimated 84% of time spent in the Australian Fishing Zone. SBT favored temperatures between 19 and 21°C, adjusting their depth to the vertical temperature distribution. Distinct diurnal diving patterns were observed and adjustment of depth to maintain constant ambient light levels over a 24‐h period. The findings of this study are a significant advance toward greater understanding of the spatial dynamics of large SBT and understanding the connectivity between distant regions of their distribution.