The human footprint in the carbon cycle of temperate and boreal forests

Temperate and boreal forests in the Northern Hemisphere cover an area of about 2 x 10(7) square kilometres and act as a substantial carbon sink (0.6-0.7 petagrams of carbon per year). Although forest expansion following agricultural abandonment is certainly responsible for an important fraction of this carbon sink activity, the additional effects on the carbon balance of established forests of increased atmospheric carbon dioxide, increasing temperatures, changes in management practices and nitrogen deposition are difficult to disentangle, despite an extensive network of measurement stations. The relevance of this measurement effort has also been questioned, because spot measurements fail to take into account the role of disturbances, either natural (fire, pests, windstorms) or anthropogenic (forest harvesting). Here we show that the temporal dynamics following stand-replacing disturbances do indeed account for a very large fraction of the overall variability in forest carbon sequestration. After the confounding effects of disturbance have been factored out, however, forest net carbon sequestration is found to be overwhelmingly driven by nitrogen deposition, largely the result of anthropogenic activities. The effect is always positive over the range of nitrogen deposition covered by currently available data sets, casting doubts on the risk of widespread ecosystem nitrogen saturation under natural conditions. The results demonstrate that mankind is ultimately controlling the carbon balance of temperate and boreal forests, either directly (through forest management) or indirectly (through nitrogen deposition).     

Low beta diversity of herbivorous insects in tropical forests

Recent advances in understanding insect communities in tropical forests have contributed little to our knowledge of large-scale patterns of insect diversity, because incomplete taxonomic knowledge of many tropical species hinders the mapping of their distribution records. This impedes an understanding of global biodiversity patterns and explains why tropical insects are under-represented in conservation biology. Our study of approximately 500 species from three herbivorous guilds feeding on foliage (caterpillars, Lepidoptera), wood (ambrosia beetles, Coleoptera) and fruit (fruitflies, Diptera) found a low rate of change in species composition (beta diversity) across 75,000 square kilometres of contiguous lowland rainforest in Papua New Guinea, as most species were widely distributed. For caterpillars feeding on large plant genera, most species fed on multiple host species, so that even locally restricted plant species did not support endemic herbivores. Large plant genera represented a continuously distributed resource easily colonized by moths and butterflies over hundreds of kilometres. Low beta diversity was also documented in groups with differing host specificity (fruitflies and ambrosia beetles), suggesting that dispersal limitation does not have a substantial role in shaping the distribution of insect species in New Guinea lowland rainforests. Similar patterns of low beta diversity can be expected in other tropical lowland rainforests, as they are typically situated in the extensive low basins of major tropical rivers similar to the Sepik-Ramu region of New Guinea studied here.     

Drought sensitivity shapes species distribution patterns in tropical forests

Although patterns of tree species distributions along environmental gradients have been amply documented in tropical forests, mechanisms causing these patterns are seldom known. Efforts to evaluate proposed mechanisms have been hampered by a lack of comparative data on species' reactions to relevant axes of environmental variation. Here we show that differential drought sensitivity shapes plant distributions in tropical forests at both regional and local scales. Our analyses are based on experimental field assessments of drought sensitivity of 48 species of trees and shrubs, and on their local and regional distributions within a network of 122 inventory sites spanning a rainfall gradient across the Isthmus of Panama. Our results suggest that niche differentiation with respect to soil water availability is a direct determinant of both local- and regional-scale distributions of tropical trees. Changes in soil moisture availability caused by global climate change and forest fragmentation are therefore likely to alter tropical species distributions, community composition and diversity.     

Density dependence explains tree species abundance and diversity in tropical forests

The recurrent patterns in the commonness and rarity of species in ecological communities--the relative species abundance--have puzzled ecologists for more than half a century. Here we show that the framework of the current neutral theory in ecology can easily be generalized to incorporate symmetric density dependence. We can calculate precisely the strength of the rare-species advantage that is needed to explain a given RSA distribution. Previously, we demonstrated that a mechanism of dispersal limitation also fits RSA data well. Here we compare fits of the dispersal and density-dependence mechanisms for empirical RSA data on tree species in six New and Old World tropical forests and show that both mechanisms offer sufficient and independent explanations. We suggest that RSA data cannot by themselves be used to discriminate among these explanations of RSA patterns--empirical studies will be required to determine whether RSA patterns are due to one or the other mechanism, or to some combination of both.     

西双版纳热带森林中原生林与次生林内鸟类对不同颜色果实的选择

果实颜色是影响食果动物取食行为的重要因素之一,同时也影响植物的种子传播.试验地点位于西双版纳野象谷自然保护区和补蚌自然保护区,在每个自然保护区内选取原生林和次生林各1处,使用红、橙、黑、蓝4种颜色的人工果实来研究鸟类对不同颜色果实的选择.试验发现,不同颜色果实在原生林中被取食的程度有显著差异,而在次生林中不存在显著差异.与以往研究结果不同,鸟类对蓝色和橙色果实的选择较为突出,而黑色果实在2处生境中的被取食均较少.     

Primary forests are irreplaceable for sustaining tropical biodiversity

Human-driven land-use changes increasingly threaten biodiversity, particularly in tropical forests where both species diversity and human pressures on natural environments are high. The rapid conversion of tropical forests for agriculture, timber production and other uses has generated vast, human-dominated landscapes with potentially dire consequences for tropical biodiversity. Today, few truly undisturbed tropical forests exist, whereas those degraded by repeated logging and fires, as well as secondary and plantation forests, are rapidly expanding. Here we provide a global assessment of the impact of disturbance and land conversion on biodiversity in tropical forests using a meta-analysis of 138 studies. We analysed 2,220 pairwise comparisons of biodiversity values in primary forests (with little or no human disturbance) and disturbed forests. We found that biodiversity values were substantially lower in degraded forests, but that this varied considerably by geographic region, taxonomic group, ecological metric and disturbance type. Even after partly accounting for confounding colonization and succession effects due to the composition of surrounding habitats, isolation and time since disturbance, we find that most forms of forest degradation have an overwhelmingly detrimental effect on tropical biodiversity. Our results clearly indicate that when it comes to maintaining tropical biodiversity, there is no substitute for primary forests.     

Low host specificity of herbivorous insects in a tropical forest

Two decades of research have not established whether tropical insect herbivores are dominated by specialists or generalists. This impedes our understanding of species coexistence in diverse rainforest communities. Host specificity and species richness of tropical insects are also key parameters in mapping global patterns of biodiversity. Here we analyse data for over 900 herbivorous species feeding on 51 plant species in New Guinea and show that most herbivorous species feed on several closely related plant species. Because species-rich genera are dominant in tropical floras, monophagous herbivores are probably rare in tropical forests. Furthermore, even between phylogenetically distant hosts, herbivore communities typically shared a third of their species. These results do not support the classical view that the coexistence of herbivorous species in the tropics is a consequence of finely divided plant resources; non-equilibrium models of tropical diversity should instead be considered. Low host specificity of tropical herbivores reduces global estimates of arthropod diversity from 31 million (ref. 1) to 4 6 million species. This finding agrees with estimates based on taxonomic collections, reconciling an order of magnitude discrepancy between extrapolations of global diversity based on ecological samples of tropical communities with those based on sampling regional faunas.     

Observations of increased tropical rainfall preceded by air passage over forests

Vegetation affects precipitation patterns by mediating moisture, energy and trace-gas fluxes between the surface and atmosphere. When forests are replaced by pasture or crops, evapotranspiration of moisture from soil and vegetation is often diminished, leading to reduced atmospheric humidity and potentially suppressing precipitation. Climate models predict that large-scale tropical deforestation causes reduced regional precipitation, although the magnitude of the effect is model and resolution dependent. In contrast, observational studies have linked deforestation to increased precipitation locally but have been unable to explore the impact of large-scale deforestation. Here we use satellite remote-sensing data of tropical precipitation and vegetation, combined with simulated atmospheric transport patterns, to assess the pan-tropical effect of forests on tropical rainfall. We find that for more than 60 per cent of the tropical land surface (latitudes 30 degrees south to 30 degrees north), air that has passed over extensive vegetation in the preceding few days produces at least twice as much rain as air that has passed over little vegetation. We demonstrate that this empirical correlation is consistent with evapotranspiration maintaining atmospheric moisture in air that passes over extensive vegetation. We combine these empirical relationships with current trends of Amazonian deforestation to estimate reductions of 12 and 21 per cent in wet-season and dry-season precipitation respectively across the Amazon basin by 2050, due to less-efficient moisture recycling. Our observation-based results complement similar estimates from climate models, in which the physical mechanisms and feedbacks at work could be explored in more detail.     

Response to seasonal change of insect resources in Changbai Mountain temperate forests by Greater Horseshoe bats

Knowing how bats select different habitats in response to environmental changes provides a framework for anticipating the likely consequences of changes in climate or vegetation. In this study we assessed the presence of greater horseshoe bats (Rhinolophus ferrumequinum) and their foraging behavior. This study depicts an effective approach for seasonal responses of habitat selection by Chiroptera.     

上海地区鳞翅目昆虫调查初步名录

在调查、采集昆虫的基础上,根据标本鉴定的结果,总结了上海地区鳞翅目昆虫调查初步名录,共计21科、83种．     

植物内生菌及其宿主植物研究概况

植物内生菌是一类重要的微生物资源库,内生菌及其次生代谢产物的研究近几年被人们广泛关注.文章对植物内生菌的宿主植物种类进行系统的阐述,现已经报道并倍受关注的宿主植物分布在77科153个属中,共有190种植物,并对分离出的内生菌分类以及其次生物质的作用进行了简要叙述.     

ARM-Linux下USB主机驱动程序研究与实现

Linux操作系统由于其源码开放、具有可裁剪等特点在嵌入式系统中得到越来越广泛的应用,而USB接口在嵌入式系统中的应用也十分广泛,现在的嵌入式系统的硬件平台大多数是基于ARM处理器的。文中介绍基于ARM平台的Linux2.6内核下,嵌入式USB主机设备驱动开发实现。具体的从USB设备驱动的开发流程出发,介绍了USB接口的一般原理和USB通信的一般过程,然后对USB驱动骨架进行了分析,最后给出了驱动具体实现的关键代码。     

Windows虚拟主机的数据库安全与防范

随着计算机网络的普及与发展,虚拟主机的用户越来越多,数据库的安全性也越来越受到人们的广泛重视。分析数据库安全隐患,提出防范措施对提高虚拟主机数据库的安全性有着重要的意义。     

肠道细菌与宿主共生的研究进展

从早期的微生物学家巴斯德(Pasteur)和梅基尼可夫(Mechnikov)到今天的微生物学家一直强调理解微生物区系在人类健康和疾病中的重要性.然而,由于肠道微生物区系的组成和结构复杂,长期以来我们对其发挥生理功能的作用机制一直了解甚少.随着分子生物学技术的发展和无菌动物的成功繁殖,为我们全面地了解肠道微生物区系的生理功能提供了有力的工具.     

浙江省公益林中杉阔混交林群落组成与环境解释

【目的】分析浙江省公益林中对杉阔混交林和阔杉混交林群落组成及其分布影响最为显著的环境因子,为亚热带杉木人工林珍贵化改造和珍贵树种保护提供合理的科学依据。【方法】采用双向指示种分析(TWINSPAN)和典范对应分析(CCA)方法,针对分布于浙江省的427个杉阔混交林和阔杉混交林样地进行物种组成及群落结构分析。【结果】杉阔混交林可划分为5类群丛,阔杉混交林可划分为6类群丛。在杉阔混交林的5类群丛中与杉木伴生的树种主要为青冈(Quercus glauca)、木荷(Schima superba)、马尾松(Pinus massoniana)和黄山松(Pinus taiwanensis)等;土壤厚度、坡向和坡度等是影响杉阔混交林群丛分布的主要环境因子。在阔杉混交林的6类群丛中,与杉木伴生的树种分别为马尾松、板栗(Castanea mollissima)、青冈、木荷、毛竹(Phyllostachys edulis)等;林龄、坡度和海拔等因素是影响阔杉混交林群落分布的主要环境因子。在杉阔混交林中,小叶青冈(Cyclobalanopsis myrsinifolia)、红楠(Machilus thunbergii)、鹅掌楸(Liriodendron chinense)、甜槠(Castanopsis eyrei)和光皮桦(Betula luminifera)等珍贵树种与杉木对生境的选择较为接近;在阔杉混交林中,甜槠、天竺桂(Cinnamomum japonicum)、小叶青冈、柳杉(Cryptomeria japonica)、苦槠(Castanopsis sclerophylla)和青冈等珍贵阔叶树种与杉木对环境的选择较为接近。【结论】选择与杉木生境接近的伴生珍贵阔叶树种进行补植改造,可以有效提高造林成活率,有利于促进杉木人工林阔叶化进程。     

A newly discovered Roseobacter cluster in temperate and polar oceans

Bacterioplankton phylotypes of alpha-Proteobacteria have been detected in various marine regions, but systematic biogeographical studies of their global distribution are missing. Alpha-Proteobacteria comprise one of the largest fractions of heterotrophic marine bacteria and include two clades, SAR11 and Roseobacter, which account for 26 and 16% of 16S ribosomal RNA gene clones retrieved from marine bacterioplankton. The SAR11 clade attracted much interest because related 16S rRNA gene clones were among the first groups of marine bacteria to be identified by cultivation-independent approaches and appear to dominate subtropical surface bacterioplankton communities. Here we report on the global distribution of a newly discovered cluster affiliated to the Roseobacter clade, comprising only as-yet-uncultured phylotypes. Bacteria of this cluster occur from temperate to polar regions with highest abundance in the Southern Ocean, but not in tropical and subtropical regions. Between the south Atlantic subtropical front and Antarctica, we detected two distinct phylotypes, one north and one south of the polar front, indicating that two adjacent but different oceanic provinces allow the persistence of distinct but closely related phylotypes. These results suggest that the global distribution of major marine bacterioplankton components is related to oceanic water masses and controlled by their environmental and biogeochemical properties.