A review of diversity-stability relationship of soil microbial community: What do we not know?

The impact of decreased biodiversity on ecosystem stability, or the diversity-stability (D-S) relationship, is one of the major concerns of modern ecological studies. Studies on the D-S relationship for soil microbial communities began in 2000 when the fumigation method was developed to generate different levels of soil microbial biodiversity. The studies used various measures and levels of biodiversity, and covered several functional parameters. Due to the lack of general concepts and reliable approaches to define microbial species, studies on the D-S relationship of soil microbial communities concentrate on genetic diversity and functional diversity more than species diversity. Contradictory results were observed in various studies on D-S relationship with possible factors affecting or even changing the directions of the D-S relationship including: (1) the methods of stability measurement, (2) the techniques in microbial diversity measurement, (3) the measures and levels of diversity, (4) the type and strength of disturbance, (5) the traits of functions, and (6) the hidden treatments stemming from diversity manipulation. We argue that future studies should take diversity, species composition and interaction, and soil environmental conditions holistically into account in D-S studies to develop modeling to predict soil functional stability. We also suggest that studies should be carried out on a wider range of disturbance types and functional parameters, and efforts be shifted towards long-term field studies.     

Preemptive and Salvage Harvesting of New England Forests: When Doing Nothing Is a Viable Alternative

Abstract:  One unexpected consequence of natural disturbances in forested areas is that managers often initiate activities that may impose greater ecosystem impacts than the disturbances themselves. By salvage logging areas affected by windstorms or other impacts, by harvesting host trees in advance of insect infestation or disease, or by preemptively harvesting forests in an attempt to improve their resilience to future disturbances and stresses, managers initiate substantial changes in the ecosystem structure and function. Much of this activity is undertaken in the absence of information on the qualitative and quantitative differences between disturbance impacts and harvesting. To provide insight for such decisions we evaluated the ecosystem consequences of two major disturbance processes in New England (U.S.A.)—intense windstorms and invasive pests and pathogens—and contrasted them with impacts from preemptive and salvage harvesting. Despite dramatic physical changes in forest structure resulting from hurricane impacts and insect infestation, little disruption of biogeochemical processes or other ecosystem functions typically follows these disturbances. Indeed, the physical and organic structures produced by these disturbances are important natural features providing habitat and landscape heterogeneity that are often missing due to centuries of land use. From an ecosystem perspective there are strong arguments against preemptive and salvage logging or the attempt through silvicultural means to improve the resistance or resilience of forests to disturbance and stress. There are often valid motivations for salvage or preemptive logging including financial considerations, human safety, and a desire to shape the long-term composition and resource-production characteristics of forests. Nonetheless, there are many ecological benefits derived from leaving forests alone when they are affected or threatened by disturbances and pest and pathogen outbreaks.     

Variation in Physiological Stress between Bridge‐ and Cave‐Roosting Brazilian Free‐Tailed Bats

Abstract: Since the late 1980s, Brazilian free‐tailed bats (Tadarida brasiliensis) have increasingly used bridges as roosts in the southern United States. We examined differences in blood cortisol levels, body condition, and parasite load, as measures of physiological stress in bats roosting in bridges and bats roosting in caves. We collected data during three periods, coinciding with female phases of reproduction. For all measures, bats were captured during the nightly emergence from the roost and immediately sampled. Cortisol levels were significantly higher during pregnancy and lactation and in individuals with lower body‐condition scores (length of forearm to mass ratio) and significantly higher in bats roosting in caves than in those roosting in bridges. Thus, we concluded that individuals of this species that roost in bridges are not chronically stressed and seem to be unaffected by human activities present at bridges. This is a rare documented instance where a human‐dominated environment does not appear to be adversely affecting the physiological health of a free‐ranging animal.     

Disturbance-Response Analysis: a Method for Rapid Assessment of the Threat to Species in Disturbed Areas

Abstract:  We developed a method with which to analyze a specie's response to chronic anthropogenic disturbance (CAD). We regressed density of individuals on the intensity of 3 disturbance agents (human activities, raising livestock, and land degradation) along CAD gradients to determine how much CAD is experienced by a species; whether species are ruderal (achieving maximum densities in disturbed sites); whether density declines as a result of CAD; which disturbance agents are responsible for this reduction; and the number of populations that decline as a result of CAD. We tested the method on 9 threatened Mammillaria species (Cactaceae). Seven species were ruderal. In 4 species, actual disturbance surpassed the CAD intensity in which plants achieved their maximum densities; thus, the density of those 4 species appeared to be declining. For 7 species, some populations were threatened by human activities or livestock, whereas others were favored by them. Land degradation negatively affected all species. Our results allowed us to distinguish 4 groups of species that had similar responses and thus may require different forms of management. Our method provided an estimation of the growth rate (λ) of the studied populations that was significantly correlated with λs obtained from demographic studies. The size structures of populations were consistent with the predictions of the analysis, which suggests our results are consistent and reliable. Disturbance–response analysis provides a basis for management in heavily populated areas, where conservation must be achieved along with development activities that cause CAD. The method provides readily interpretable information, which facilitates participative decision making; the data are rapidly generated, which makes it appropriate when results are required promptly or for assessment of large numbers of species; and it provides a comprehensive perception of how threatened species behave in the real world.     

人为干扰对马尾松次生林多样性的影响

利用Ｓｈａｎｎｏｎ多样性指数和均匀度来分析人为干扰对马尾松次生林木本植物多样性的影响，结果表明：马尾松次生林木本植物多样性指数为２左右（１．８５７９～２．１９４６），均匀度为０．７左右（０．７２４４～０．７７４６），物种多度分布符合对数级数分布，不同干扰强度对多样性和均匀度有一定影响，对物种多度分布没有影响，对马尾松林的更新有重要作用。     

玉龙雪山牦牛坪高山草甸的干扰格局分析

近几年玉龙雪山生态旅游热升温,对该区域生态环境和植被资源的影响日趋显著,研究该区域高山草甸所受干扰对制定该区域的生态保护、可持续发展对策具有重要意义。为明晰人类活动对玉龙雪山高山草甸的影响,选取该区域典型高山草甸分布区域作为研究区,分析其草甸退化格局,通过干扰强度模型量化研究区的干扰格局,并利用方差分解确定不同干扰对高山草甸退化的贡献率。结果表明：（1）放牧干扰主要集中在牲畜饮水点附近,旅游干扰更多作用于景区观景台和寺庙附近,干扰活动分布与路径体系相吻合,游径布设和游客行为扩散模式决定了旅游干扰的格局;（2）草甸退化程度随干扰程度的增加而升高,干扰强度最大的区域与草甸的重度退化区域重合;（3）总体上旅游较放牧对草甸退化的贡献作用更大,但存在空间差异。在玉龙雪山牦牛坪景区,旅游干扰已逐渐取代放牧干扰成为主要干扰因素,且路径体系与旅游干扰格局具有较高的吻合度,对草甸退化格局的影响在逐渐增加。综上,建议选取使用率高的非正式路径修建为正式路径,保护和恢复分布在使用率低的非正式路径旁的植被和土壤,以降低旅游干扰对高山草甸的影响。     

CDN辐射骚扰测试影响因素的探究

研究影响CISPR15中辐射骚扰测试项目所用的电波暗室测试法的替代方法（CDN法）的测试因素。通过在不同的测试环境、不同的布置下对比测试,得到了不同的测试结果,从而加深了对标准布置的理解,也为实验室间比对测试提供了参考。     

电源适配器输出端口骚扰电压测量方法

电源适配器的直流输出端口骚扰电压过高会造成笔记本计算机电信端口传导骚扰电压测试不合格,但是标准中缺乏直流输出端口骚扰电压的测量方法。设计了一种电源适配器直流输出端口传导骚扰电压测量方法,在不需要配置笔记本计算机的环境下使用电源适配器单体模拟电信端口测试,其测量结果可以用于预测电源适配器在笔记本电脑电信端口产生的共模传导骚扰电压。经实际实验结果,用此方法测得的直流输出端口骚扰电压谱线与搭配笔记本计算机后的电信端口骚扰谱线有很好的对应性。     

高速动车组车内低频电磁场测试及分布特性分析

近年来我国高速铁路建设飞速发展,在给交通运输带来了方便快捷的同时,也引入了电磁干扰问题。本文以高速动车组车内低频电磁环境为对象,分析了高速铁路电磁骚扰源及列车产生电磁骚扰的机理,通过对大量实测数据的统计和总结,分析了高速动车组车内低频电磁场的分布和规律,并对我国高速动车组车内低频电磁环境的优化提出一些看法和建议。