Parasitic plants indirectly regulate below-ground properties in grassland ecosystems

Parasitic plants are one of the most ubiquitous groups of generalist parasites in both natural and managed ecosystems, with over 3,000 known species worldwide. Although much is known about how parasitic plants influence host performance, their role as drivers of community- and ecosystem-level properties remains largely unexplored. Parasitic plants have the potential to influence directly the productivity and structure of plant communities because they cause harm to particular host plants, indirectly increasing the competitive status of non-host species. Such parasite-driven above-ground effects might also have important indirect consequences through altering the quantity and quality of resources that enter soil, thereby affecting the activity of decomposer organisms. Here we show in model grassland communities that the parasitic plant Rhinanthus minor, which occurs widely throughout Europe and North America, has strong direct effects on above-ground community properties, increasing plant diversity and reducing productivity. We also show that these direct effects of R. minor on the plant community have marked indirect effects on below-ground properties, ultimately increasing rates of nitrogen cycling. Our study provides evidence that parasitic plants act as a major driver of both above-ground and below-ground properties of grassland ecosystems.     

Effect of animal husbandry on herbivore-carrying capacity at a regional scale.

All significant properties of the herbivore trophic level, including biomass, consumption and productivity, are significantly correlated with primary productivity across a broad range of terrestrial ecosystems. Here we show that livestock biomass in South American agricultural ecosystems across a 25-fold gradient of primary productivity exhibited a relationship with a slope essentially identical to unmanaged ecosystems, but with a substantially greater y-intercept. Therefore the biomass of herbivores supported per unit of primary productivity is about an order of magnitude greater in agricultural than in natural ecosystems, for a given level of primary production. We also present evidence of an increase in livestock body size with primary productivity, a pattern previously characterized in natural ecosystems. To our knowledge this is the first quantitative documentation at a regional scale of the impact of animal husbandry practices, such as herding, stock selection and veterinary care, on the biomass and size-structure of livestock herds compared with native herbivores.     

The effect of migration on local adaptation in a coevolving host-parasite system

Antagonistic coevolution between hosts and parasites in spatially structured populations can result in local adaptation of parasites; that is, the greater infectivity of local parasites than foreign parasites on local hosts. Such parasite specialization on local hosts has implications for human health and agriculture. By contrast with classic single-species population-genetic models, theory indicates that parasite migration between subpopulations might increase parasite local adaptation, as long as migration does not completely homogenize populations. To test this hypothesis we developed a system-specific mathematical model and then coevolved replicate populations of the bacterium Pseudomonas fluorescens and a parasitic bacteriophage with parasite only, with host only or with no migration. Here we show that patterns of local adaptation have considerable temporal and spatial variation and that, in the absence of migration, parasites tend to be locally maladapted. However, in accord with our model, parasite migration results in parasite local adaptation, but host migration alone has no significant effect.     

Upwelling-driven nearshore hypoxia signals ecosystem and oceanographic changes in the northeast Pacific

Seasonal development of dissolved-oxygen deficits (hypoxia) represents an acute system-level perturbation to ecological dynamics and fishery sustainability in coastal ecosystems around the globe. Whereas anthropogenic nutrient loading has increased the frequency and severity of hypoxia in estuaries and semi-enclosed seas, the occurrence of hypoxia in open-coast upwelling systems reflects ocean conditions that control the delivery of oxygen-poor and nutrient-rich deep water onto continental shelves. Upwelling systems support a large proportion of the world's fisheries, therefore understanding the links between changes in ocean climate, upwelling-driven hypoxia and ecological perturbations is critical. Here we report on the unprecedented development of severe inner-shelf (<70 m) hypoxia and resultant mass die-offs of fish and invertebrates within the California Current System. In 2002, cross-shelf transects revealed the development of abnormally low dissolved-oxygen levels as a response to anomalously strong flow of subarctic water into the California Current System. Our findings highlight the sensitivity of inner-shelf ecosystems to variation in ocean conditions, and the potential impacts of climate change on marine communities.     

亚热带常绿阔叶林不同林龄细根生物量及其养分

通过对安徽池州老山自然保护区的肖坑常绿阔叶林细根生物量和细根养分进行研究,发现细根生物量和细根养分及养分储量呈明显的垂直分布规律,即随着土层加深而逐渐减少。在表土层,0~10 cm土层中细根生物量最多,氮、磷、钾含量及其养分储量也是最高。对不同年龄阶段的常绿阔叶林比较发现,细根的生物量有随着林分年龄的增加而增加的趋势,而不同年龄林分细根中氮、磷、钾的含量也存在一定差异。     

Reconciling the temperature dependence of respiration across timescales and ecosystem types

Ecosystem respiration is the biotic conversion of organic carbon to carbon dioxide by all of the organisms in an ecosystem, including both consumers and primary producers. Respiration exhibits an exponential temperature dependence at the subcellular and individual levels, but at the ecosystem level respiration can be modified by many variables including community abundance and biomass, which vary substantially among ecosystems. Despite its importance for predicting the responses of the biosphere to climate change, it is as yet unknown whether the temperature dependence of ecosystem respiration varies systematically between aquatic and terrestrial environments. Here we use the largest database of respiratory measurements yet compiled to show that the sensitivity of ecosystem respiration to seasonal changes in temperature is remarkably similar for diverse environments encompassing lakes, rivers, estuaries, the open ocean and forested and non-forested terrestrial ecosystems, with an average activation energy similar to that of the respiratory complex (approximately 0.65?electronvolts (eV)). By contrast, annual ecosystem respiration shows a substantially greater temperature dependence across aquatic (approximately 0.65?eV) versus terrestrial ecosystems (approximately 0.32?eV) that span broad geographic gradients in temperature. Using a model derived from metabolic theory, these findings can be reconciled by similarities in the biochemical kinetics of metabolism at the subcellular level, and fundamental differences in the importance of other variables besides temperature—such as primary productivity and allochthonous carbon inputs—on the structure of aquatic and terrestrial biota at the community level.     

Effects of macrophyte species richness on wetland ecosystem functioning and services

Wetlands provide many important ecosystem services to human society, which may depend on how plant diversity influences biomass production and nutrient retention. Vascular aquatic plant diversity may not necessarily enhance wetland ecosystem functioning, however, because competition among these plant species can be strong, often resulting in the local dominance of a single species. Here we have manipulated the species richness of rooted, submerged aquatic plant (macrophyte) communities in experimental wetland mesocosms. We found higher algal and total plant (algal plus macrophyte) biomass, as well as lower loss of total phosphorus, in mesocosms with a greater richness of macrophyte species. Greater plant biomass resulted from a sampling effect; that is, the increased chance in species mixtures that algal production would be facilitated by the presence of a less competitive species-in this case, crisped pondweed. Lower losses of total phosphorus resulted from the greater chance in species mixtures of a high algal biomass and the presence of sago pondweed, which physically filter particulate phosphorus from the water. These indirect and direct effects of macrophyte species richness on algal production, total plant biomass and phosphorus loss suggest that management practices that maintain macrophyte diversity may enhance the functioning and associated services of wetland ecosystems.     

Rapid worldwide depletion of predatory fish communities

Serious concerns have been raised about the ecological effects of industrialized fishing, spurring a United Nations resolution on restoring fisheries and marine ecosystems to healthy levels. However, a prerequisite for restoration is a general understanding of the composition and abundance of unexploited fish communities, relative to contemporary ones. We constructed trajectories of community biomass and composition of large predatory fishes in four continental shelf and nine oceanic systems, using all available data from the beginning of exploitation. Industrialized fisheries typically reduced community biomass by 80% within 15 years of exploitation. Compensatory increases in fast-growing species were observed, but often reversed within a decade. Using a meta-analytic approach, we estimate that large predatory fish biomass today is only about 10% of pre-industrial levels. We conclude that declines of large predators in coastal regions have extended throughout the global ocean, with potentially serious consequences for ecosystems. Our analysis suggests that management based on recent data alone may be misleading, and provides minimum estimates for unexploited communities, which could serve as the 'missing baseline' needed for future restoration efforts.     

洪湖湿地野菰群落储碳、固碳功能研究

通过实地调研与实验室测定相结合的方法,研究洪湖湿地野菰（Zizania latifolia）的现存生物量和初级生产力,测算其碳储量、固碳能力,探讨其固碳潜力.结果得出：洪湖湿地野菰地上现存生物量平均0.75kg.m-2（0.52～0.96kg.m-2）,现存碳储量平均0.33kg.m-2（0.23～0.42kg.m-2）;地下部分的生物现存量平均为1.47kg.m-2,其碳储量平均为0.65kg.m-2,均约为地上2倍,因此野菰碳储量主要在地下部分;洪湖湿地野菰地上部分净初级生产力平均合计达0.75kg.m-2.a-1,加上地下部分,平均为1.2kg.m-2.a-1,固碳能力为0.53kg.m-2.a-1,高于全国陆地植被平均固碳能力和全球植被平均固碳能力.与中国不同生态系统的固碳能力相比,由于洪湖湿地野菰种群郁闭度较高,其平均固碳能力强于城市、河流等生态系统,明显高于其他湖泊生态系统.     

Do plants explore habitats before exploiting them? An explicit test using two stoloniferous herbs

We tested whether the processes of exploration and exploitation can be explicitly distinguished as plants grow and develop within a habitat using two stoloniferous clonal herbs,Hydrocotyle sibthorpioides(Umbelliferae) and Potentilla anserina(Rosaceae).Ramets were planted in four circular trays differing in diameter.One replicate from each diameter-group was sampled at intervals corresponding to plant coverage of the trays,and plant biomass allocation to leaves,stolons,and roots and internode length were quantified.For both species,at early sampling times(when the smallest trays were full),total plant biomass and ramet number were larger in the smaller trays than in the larger trays.However,this trend was reversed for plants collected at later times.For H.sibthorpioides,leaf mass ratios(leaf mass to total plant mass) were significantly greater,but stolon mass ratios(stolon mass to total plant mass) were less in the small trays than in the larger ones,particularly during the early stages of the experiment.Similarly,for P.anserina,leaf mass ratios decreased in the smaller trays but increased in the larger ones as the experiment progressed.Root mass ratios showed contrasting pattern to leaf mass ratios for both species;stolon mass ratios were significantly smaller in the smaller trays than in the larger ones,although there were no obvious patterns during the course of the experiment.In addition,for both species,internode length was shorter but the number of ramets was greater in the smaller trays at early sampling times.We conclude that plants invest greater biomass in resource-exploring organs(stolons) than in resource-exploiting organs(leaves or roots) as they initially establish in a habitat.The relatively lower plant productivity in the largest trays at early sampling times presumably reflects the cost of exploration prior to resource exploitation and utilization.     

Plant litter decomposition in a semi-arid ecosystem controlled by photodegradation

The carbon balance in terrestrial ecosystems is determined by the difference between inputs from primary production and the return of carbon to the atmosphere through decomposition of organic matter. Our understanding of the factors that control carbon turnover in water-limited ecosystems is limited, however, as studies of litter decomposition have shown contradictory results and only a modest correlation with precipitation. Here we evaluate the influence of solar radiation, soil biotic activity and soil resource availability on litter decomposition in the semi-arid Patagonian steppe using the results of manipulative experiments carried out under ambient conditions of rainfall and temperature. We show that intercepted solar radiation was the only factor that had a significant effect on the decomposition of organic matter, with attenuation of ultraviolet-B and total radiation causing a 33 and 60 per cent reduction in decomposition, respectively. We conclude that photodegradation is a dominant control on above-ground litter decomposition in this semi-arid ecosystem. Losses through photochemical mineralization may represent a short-circuit in the carbon cycle, with a substantial fraction of carbon fixed in plant biomass being lost directly to the atmosphere without cycling through soil organic matter pools. Furthermore, future changes in radiation interception due to decreased cloudiness, increased stratospheric ozone depletion, or reduced vegetative cover may have a more significant effect on the carbon balance in these water-limited ecosystems than changes in temperature or precipitation.     

Evaluating cellulose absorption index （CAI） for non-photosynthetic biomass estimation in the desert steppe of Inner Mongolia

Accurate estimation of non-photosynthetic biomass is critical for modeling carbon dynamics within grassland ecosystems.We evaluated the cellulose absorption index(CAI),widely used for monitoring non-photosynthetic vegetation coverage,for non-photosynthetic biomass estimation.Our analysis was based on in situ hyperspectral measurements,during the growing seasons of 2009 and 2010,in the desert steppe of Inner Mongolia.ASD(Analytical Spectral Device)-derived and Hyperion-derived CAI were found to be effective for non-photosynthetic biomass estimation,yielding relative error(RE) values of 26.4% and 26.6%,respectively.The combination of MODIS(Moderate Resolution Imaging Spectroradiometer)-derived(MODIS2 MODIS5)/(MODIS2 +MODIS5) and(MODIS6 MODIS7)/(MODIS6 +MODIS7) showed a high multiple correlation(multiple correlation coefficient,r=0.884) with ASD-derived CAI.A predictive model involving the two MODIS indices gave greater accuracy(RE=28.9%) than the TM(Landsat Thematic Mapper)-derived indices.The latter were the normalized difference index(NDI),the soil adjusted corn residue index(SACRI),and the modified soil adjusted crop residue index(MSACRI).These indices yielded RE values of more than 42%.Our conclusions have great significance for the estimation of regional non-photosynthetic biomass in grasslands,based on remotely sensed data.     

1998-2002年我国陆地植被变化探测研究

以长时间序列VGT-NDVI为数据源,利用年内变异系数与年份回归分析的方法对1998-2002年间的中国陆地植被NDVI的变化情况进行了分析.中国大部分地区线性回归相关性显著,整体相关系数为0.78.研究结果表明,在这五年间,中国北方的植被覆盖呈增加状态,而南部地区的植被覆盖情况则有明显的减少趋势.总体来讲,中国的西部变动情况大于东部,并且西北呈增加趋势,西南则呈减少趋势.     

南海北部大陆架海洋生态系统Ecopath模型的应用与分析

过度捕捞和环境恶化导致渔业资源和海洋生态系统逆向发展。采用EwE5.1软件,对南海北部大陆架建立Ecopath(生态通道模型)模型。通过各级流量、生物量、生产量、捕捞量、系统总流量以及生态位和混和营养效应等方面的分析,得出营养流通主要有2种途径,肉食鱼类间饵料竞争非常激烈,低值鱼类间具相似的捕食压力,顶级捕食者对大部分鱼类负效应不明显。系统受过度捕捞渔业影响很大,并存在营养级I利用效率低和渔业资源小型化、低值化等不稳定的幼态特征。     

Net carbon dioxide losses of northern ecosystems in response to autumn warming

The carbon balance of terrestrial ecosystems is particularly sensitive to climatic changes in autumn and spring, with spring and autumn temperatures over northern latitudes having risen by about 1.1 degrees C and 0.8 degrees C, respectively, over the past two decades. A simultaneous greening trend has also been observed, characterized by a longer growing season and greater photosynthetic activity. These observations have led to speculation that spring and autumn warming could enhance carbon sequestration and extend the period of net carbon uptake in the future. Here we analyse interannual variations in atmospheric carbon dioxide concentration data and ecosystem carbon dioxide fluxes. We find that atmospheric records from the past 20 years show a trend towards an earlier autumn-to-winter carbon dioxide build-up, suggesting a shorter net carbon uptake period. This trend cannot be explained by changes in atmospheric transport alone and, together with the ecosystem flux data, suggest increasing carbon losses in autumn. We use a process-based terrestrial biosphere model and satellite vegetation greenness index observations to investigate further the observed seasonal response of northern ecosystems to autumnal warming. We find that both photosynthesis and respiration increase during autumn warming, but the increase in respiration is greater. In contrast, warming increases photosynthesis more than respiration in spring. Our simulations and observations indicate that northern terrestrial ecosystems may currently lose carbon dioxide in response to autumn warming, with a sensitivity of about 0.2 PgC degrees C(-1), offsetting 90% of the increased carbon dioxide uptake during spring. If future autumn warming occurs at a faster rate than in spring, the ability of northern ecosystems to sequester carbon may be diminished earlier than previously suggested.     

Mangroves enhance the biomass of coral reef fish communities in the Caribbean

Mangrove forests are one of the world's most threatened tropical ecosystems with global loss exceeding 35% (ref. 1). Juvenile coral reef fish often inhabit mangroves, but the importance of these nurseries to reef fish population dynamics has not been quantified. Indeed, mangroves might be expected to have negligible influence on reef fish communities: juvenile fish can inhabit alternative habitats and fish populations may be regulated by other limiting factors such as larval supply or fishing. Here we show that mangroves are unexpectedly important, serving as an intermediate nursery habitat that may increase the survivorship of young fish. Mangroves in the Caribbean strongly influence the community structure of fish on neighbouring coral reefs. In addition, the biomass of several commercially important species is more than doubled when adult habitat is connected to mangroves. The largest herbivorous fish in the Atlantic, Scarus guacamaia, has a functional dependency on mangroves and has suffered local extinction after mangrove removal. Current rates of mangrove deforestation are likely to have severe deleterious consequences for the ecosystem function, fisheries productivity and resilience of reefs. Conservation efforts should protect connected corridors of mangroves, seagrass beds and coral reefs.     

Biodiversity improves water quality through niche partitioning

Excessive nutrient loading of water bodies is a leading cause of water pollution worldwide, and controlling nutrient levels in watersheds is a primary objective of most environmental policy. Over the past two decades, much research has shown that ecosystems with more species are more efficient at removing nutrients from soil and water than are ecosystems with fewer species. This has led some to suggest that conservation of biodiversity might be a useful tool for managing nutrient uptake and storage, but this suggestion has been controversial, in part because the specific biological mechanisms by which species diversity influences nutrient uptake have not been identified. Here I use a model system of stream biofilms to show that niche partitioning among species of algae can increase the uptake and storage of nitrate, a nutrient pollutant of global concern. I manipulated the number of species of algae growing in the biofilms of 150 stream mesocosms that had been set up to mimic the variety of flow habitats and disturbance regimes that are typical of natural streams. Nitrogen uptake rates, as measured by using (15)N-labelled nitrate, increased linearly with species richness and were driven by niche differences among species. As different forms of algae came to dominate each unique habitat in a stream, the more diverse communities achieved a higher biomass and greater (15)N uptake. When these niche opportunities were experimentally removed by making all of the habitats in a stream uniform, diversity did not influence nitrogen uptake, and biofilms collapsed to a single dominant species. These results provide direct evidence that communities with more species take greater advantage of the niche opportunities in an environment, and this allows diverse systems to capture a greater proportion of biologically available resources such as nitrogen. One implication is that biodiversity may help to buffer natural ecosystems against the ecological impacts of nutrient pollution.     

2006～2008年北京地区常用实验动物微生物和寄生虫检测结果分析

目的对2006年～2008年北京地区普通Beagle犬、大耳白兔和清洁以上大鼠(Wistar和SD品系)、小鼠(KM和ICR品系)微生物和寄生虫的抽检结果进行分析,为实验动物生产管理提供参考。方法按现行国标《实验动物微生物学检测方法》和《实验动物寄生虫学检测方法》,抽检动物所携带的微生物和寄生虫。结果普通Beagle犬的质量虽在逐渐提高,但体外寄生虫时有检出;普通大耳白兔体外寄生虫的携带较为普遍;清洁大鼠和小鼠的微生物检测结果基本合格,但有体内寄生虫的阳性样本;SPF级大鼠和小鼠的供应数量较少,尚不能充分满足科研工作的需要。建议有关实验动物生产单位加强普通动物的防疫工作,同时改进饲养管理水平,以有效避免传染病和寄生虫病的发生;加强清洁动物的净化及物料的消毒工作,以确保清洁动物的质量合格、稳定;进一步提高实验动物的净化水平并扩大SPF动物的生产规模,以充分满足科研工作的需要。     

我国当前重要人体食源性寄生虫病原

为考察我国当前重要人体食源性寄生虫病原的种类、新的流行感染方式和感染途径．本文论述了我国近几年出现的重要食源性人兽共患寄生虫病原种类，介绍病原的感染来源、感染途径和感染方式．结果经统计发现有29种食源性寄生虫病原．这些寄生虫病原的感染来源主要通过日常食物污染，经口随食物感染，并且多数为人兽共患寄生虫病原．     

Prolonged suppression of ecosystem carbon dioxide uptake after an anomalously warm year

Terrestrial ecosystems control carbon dioxide fluxes to and from the atmosphere through photosynthesis and respiration, a balance between net primary productivity and heterotrophic respiration, that determines whether an ecosystem is sequestering carbon or releasing it to the atmosphere. Global and site-specific data sets have demonstrated that climate and climate variability influence biogeochemical processes that determine net ecosystem carbon dioxide exchange (NEE) at multiple timescales. Experimental data necessary to quantify impacts of a single climate variable, such as temperature anomalies, on NEE and carbon sequestration of ecosystems at interannual timescales have been lacking. This derives from an inability of field studies to avoid the confounding effects of natural intra-annual and interannual variability in temperature and precipitation. Here we present results from a four-year study using replicate 12,000-kg intact tallgrass prairie monoliths located in four 184-m(3) enclosed lysimeters. We exposed 6 of 12 monoliths to an anomalously warm year in the second year of the study and continuously quantified rates of ecosystem processes, including NEE. We find that warming decreases NEE in both the extreme year and the following year by inducing drought that suppresses net primary productivity in the extreme year and by stimulating heterotrophic respiration of soil biota in the subsequent year. Our data indicate that two years are required for NEE in the previously warmed experimental ecosystems to recover to levels measured in the control ecosystems. This time lag caused net ecosystem carbon sequestration in previously warmed ecosystems to be decreased threefold over the study period, compared with control ecosystems. Our findings suggest that more frequent anomalously warm years, a possible consequence of increasing anthropogenic carbon dioxide levels, may lead to a sustained decrease in carbon dioxide uptake by terrestrial ecosystems.