铁路沿线沙生植物种子风传扩散的数值风洞模拟

为了研究铁路沿线沙生植物种子风传扩散机制所体现出的生态适应策略,本文以辽西北铁路沿线沙区段5种蒿属植物为研究对象,借助流体动力学方程和计算机图形学技术,采用数值风洞方法,模拟预测了在不同风速及释放高度条件下各物种种子扩散时间和扩散距离的变化趋势。软件模拟结果表明,（1）在释放高度和风速条件相同的情况下,5种蒿属植物种子的飞行时间和飞行距离与种子重量表现出相反的趋势,即随着种子重量的增大,其水平飞行时间和飞行距离减短。（2）在释放高度相同风速条件不同的情况下,5种蒿属植物种子的飞行时间和飞行距离与风速表现出相同的趋势,即种子的飞行时间和飞行距离随着风速的增大而增加。（3）在风速条件相同释放高度不同的情况下,5种蒿属植物种子的飞行时间和飞行距离与释放高度表现出相同的趋势,即种子的飞行时间和飞行距离随着释放高度的增加而增加。种子重量、风速及释放高度是影响种子扩散时间和扩散距离的敏感因素,在铁路沿线沙化地区筛选适宜的植物防沙措施进行生态修复的同时应结合考虑这些影响因素。     

Is it a hindrance for an invasive aquatic species to spread across scattered habitat patches?

1. Despite their importance for aquatic biodiversity, ponds are among the most vulnerable freshwater habitats. Owing to their isolation in terrestrial environments, ponds are expected to be relatively well protected from biological invasions, but this depends on many factors. 2. The purpose of this study was to examine the influence of a range of variables (water quality, habitat, and landscape attributes) on the colonization of discrete ponds by a widespread aquatic invader, the red swamp crayfish Procambarus clarkii, which can disperse overland. 3. Investigations were conducted in two networks of ponds, each located in close proximity to a large invaded marsh. The two marshes under study differed in the length of time since the crayfish were introduced. 4. The proportions of colonized ponds and crayfish abundances were moderate in both networks, but higher in the network that had been invaded first. In both networks the distance to the marsh was the main predictor of pond colonization, considering similar energy costs to cross aquatic and terrestrial habitats for the recently invaded network, but assuming that dispersal was 25 times costlier across the terrestrial matrix than via streams for the earlier invaded network. Pond characteristics had no influence on crayfish occurrence in either network. Furthermore, predictions of pond invasion were lower for the recently invaded network. 5. The importance of the distance to the marsh indicates that natural dispersal was the main process of pond colonization by crayfish. Findings also suggested that overland dispersal was rare and costly. By contrast, streams were probably significant in facilitating crayfish dispersal. Differences between the two networks might arise from an invasion process still in progress in the recently invaded network. 6. From a management viewpoint, local actions are encouraged to prevent the spread of crayfish via streams. In addition, broader‐scale actions to mitigate other human disturbances would improve the outlook for pond biodiversity.     

Sheep as vectors for branched broomrape (Orobanche ramosa subsp. mutelii [F.W. Schultz] Cout.) seed dispersal

Sheep can be vectors for the long‐distance dispersal of weeds when seed becomes attached and retained in wool or survives the gastrointestinal tract. This study aimed to determine an appropriate quarantine period for sheep that minimized the risk of the long‐distance dispersal of the seeds of branched broomrape (Orobanche ramosa L. subsp. mutelii [F.W. Shultz] Cout.), a parasitic weed. Experiments with penned sheep found that the seeds that were placed on the soil surface adhered to the wool on the thigh and belly of the sheep, with most of the seeds attaching to the feet. Most of the seeds that were applied to the belly and thigh wool detached within 2 days, although a small proportion was present after 7 days. The seeds that were introduced to the digestive tract via drenching had a peak voidance 2 days later and no seed was detected on Day 8. It is suggested that a 7 day quarantine period for sheep would be sufficient in order to reduce the risk of the internal transport of seed to acceptable levels, but a small risk of the external transport of seed on the fleece remains.     

转基因水稻基因飘流研究十年回顾

中国是世界最大的水稻生产国和亚洲栽培稻的起源中心之一。随着中国转基因水稻研发的快速发展,需要研究水稻转基因飘流可能对环境和食品安全带来的潜在风险。基因飘流及其数据是对转基因水稻进行科学评估和监管的重要参数。为此,从2002年开始组建了研究团队,对转基因水稻的基因飘流进行了为期10年的系统研究。取得的结果主要包括：（1）阐明了水稻基因飘流的基本规律,揭示了影响水稻基因飘流的生物学和气象学主控因子。沿水稻开花期的主流风向,采用长方形田间试验设计,分别在三亚、广州和杭州3个点2-3个生长季,研究了纯合转bar基因花粉供体L201或B2 (姐妹系,抗除草剂Basta)向19个非转基因受体（包括不育系、常规稻品种、杂交稻F1和普通野生稻）在不同距离上的基因飘流率,明确了转基因向不育系的飘流率最高,向普通栽培稻品种的基因飘流率最低(相邻种植时小于1%或0.1%),向普通野生稻的基因飘流率介于不育系和常规稻之间,向不育系的最大基因飘流率比向普通野生稻和栽培稻要大1-3个数量级;基因飘流率随距离增加呈负指数曲线衰减,且存在急剧降低的“拐点”,“拐点”的距离与试验点水稻开花期的风速密切相关,广州和杭州为1-2 m,三亚约为5 m;采用圆形、以花粉供体为中心的田间试验设计,以异交结实率很高的不育系博A作受体,清晰地解析了风向与基因飘流率的数值关系,主流和次主流风向下游4个扇区的基因飘流事件累计达90%-96%,而逆风向和侧逆风向4个扇区仅为4%-10%。综上所述,水稻转基因飘流率与常规育成品种间的异交率（一般在1%以下）基本相同,在数量级上转基因并未增加新的风险。（2）建立了以气象资料为参数的水稻花粉扩散和基因飘流普适模型,计算和预测了中国南方稻区17省、市的最大基因飘流阈值距离（maximum threshold distances, MTDs）。受东南季风和地形地貌的影响,中国南方稻区MTDs的空间分布特征为：东西之间有自东向西逐渐减小的趋势,南北之间首先在南方丘陵地区逐渐减小、越过南岭后再向东南沿海地区逐渐增大。（3）利用人工构建的普通野生稻与基因（Bt或bar）飘流后代栽/野F1杂种混栽群体,经多年多代跟踪观察,分析了转基因飘流至普通野生稻后的命运,发现栽/野F1杂种在3-5年后完全消失,混栽群体中检测不到外源的Bt和bar,有理由推测普通野生稻具有自我保护的机制。（4）研究了小规模田间试验中采用花期隔离和布帐隔离措施降低水稻基因飘流率的效果;调查了海南、广东、广西普通野生稻原生境居群与相邻种植的栽培稻花期相遇情况,建立了相应的数据库;研究了基因拆分技术作为生物学限控措施从根本上限控基因飘流的效果;以本研究的结果及对国际上主要农作物基因飘流的调研数据为基础,提出了在水稻基因飘流风险评估和监管中采用分类管理和阈值管理的原则。在10年回顾和科学分析的基础上,对未来研究的重点也进行了展望。     

Importance of hedgerows as habitat corridors for forest plants in agricultural landscapes

Hedgerows have been proposed as habitat and conservation corridor for forest plant species, but their importance for the survival of these species is still not clear. The objective of our study was to examine the frequency of occurrence of forest species and total forest species richness in different parts of the hedgerows, and to relate these patterns of occurrence to the species’ habitat requirements and life history traits. We surveyed in total 130 forest-hedgerow transects in North-western Germany, including three age classes.About 77% of all forest plant species (including some endangered taxa) occurring in the neighbouring forests were also found in the adjacent hedgerows. In all age classes, there was a negative relationship between distance from the forest-hedgerow ecotone and the number of species. Ancient hedgerows were not significantly more species-rich than more recent ones. Within 100 m distance from the forest edge, forest species richness increased with an increasing number of species in the nearby forest and with an increasing cover of the tree canopy as well as a decreasing cover of the shrub layer. Species with high frequency had comparatively high Ellenberg indicator values for light, and were mostly associated with anemochorous and epizoochorous seed dispersal.The frequency of occurrence in hedgerows of species with common attributes was partly in agreement, partly in disagreement with the results obtained in previous studies. We conclude that patterns are difficult to generalize, probably due to a strong regional variation in the pool of forest species and in the specific environments of both forests and hedgerows.     

尼加拉瓜废弃农田次生演替后的土壤种子库

定量分析了被废弃4年、9年和14年的农田地上派生的次生林土壤中种子组成和密度,从而检测在次生林演替形成过程中,土壤种子库是否能随着植物种群的集成而集成。分别在废弃了4年、9年和14年的农田地里（15cm×15cm样方、9cm土层深）,掘取了18,37和48份土壤样品。在废弃了4,9和14年的农田地上,分别发现了3,5和9个物种。在这些不同的生命形态中,在9年和14年的迹地上,土壤种子树木占主要成分,分别为60%和33%,而4年废弃迹地主要被非木本植物所占领。三块废弃地里,4年废弃迹地植物种子的总数为327粒,相应可发育的种子密度为141粒/m2,14年废弃迹地种子的总数为46粒,相应的可发育种子的密度为26粒/m^2,指明种子数、种子密度随废弃地龄成下降趋势。在9年和14年龄废弃地上,土壤种子植物种类与立地木本植物种类的相似度较低,而4年龄地上两者比较则完全不同。我们认为：土壤种子库的物种构成是在次生演替过程中逐渐形成的,但是,所获得的总体种子密度太低,仅仅依赖于这些种子来实现树木自然再生是不可靠的。为了加快这些废弃地次生林的恢复,既要依靠自然集成的土壤种子库,还需要通过直播、所需物种的强化种植和设定人工生长环境以利于种子传播。     

宁夏荒漠草原种子雨研究

近年来,有关土壤种子库研究的报道较多,但种子雨的研究较少,因此以宁夏荒漠草原为研究对象,采用样线法,以培养皿为种子雨收集器,对种子雨的散布特点及种子雨与地上植被的关系进行了研究。结果表明:种子雨的植物种类为8种,多年生草本植物所占比例较大为62.5%;种子雨的散布8—10月份为逐渐递增的趋势,10月份为种子雨散布的高峰期,8—10月份种子雨的密度分别为（73.60±12.24）个/m²,（77.85±11.81）个/m²,（240.62±41.08）个/m²;种子雨植物密度和地上植物密度没有显著的相关性;种子雨植物种和地上植物种的相似性为0.457,相似性较低。研究结果可以为种子雨、种子库、地上植被间相互关系的研究提供参考。