Palaeolimnology of Lake Hess (Patagonia,Argentina): multi-proxy analyses of short sediment cores

In contrast with the extensive palaeolimnological studies carried out in North America and Europe, relatively few studies have described the anthropogenic and/or climate impacts in Patagonian lakes. We addressed these issues by analysing geochemistry, lithology, pigments and chironomid remains from sediment cores collected from Lake Hess (41°22′20″S, 71°44′0″W) located in the Nahuel Huapi National Park in northern Patagonia. The aim of this study is to provide a palaeoenvironmental and climate reconstruction of the past ca. three centuries for this cold oligotrophic, quasi-pristine lake which receives meltwaters from the Tronador ice cap. Chronology was based on ¹³⁷Cs and ²¹⁰Pb measurements of the upper sediments, and the inferred sedimentation rate of 23.2 mg cm⁻² y⁻¹ (0.15 cm y⁻¹) was consistent with both sets of measurements. The sediment from Lake Hess was rich in tephra deposits particularly evident in the lower part of the cores. Tephras are valuable to use for core correlation and can be traced through peaks in the magnetic susceptibility (MS) profiles. Results from the multiproxy analyses in the longest core (83 cm) identify three main phases of change. From the bottom up to 42 cm (ca. ad 1800), the sediment is composed of light-grey organically rich clays. Both pigments and chironomids suggest variable trends in productivity and precipitation regime. At the end of the Little Ice Age chronozone (ad 1770–1850), pigment concentrations were very low. From 42 cm to ca. 25 cm (ad 1800–1940), the sedimentary record is composed of alternating black and dark organic-matter rich mud with variable amounts of macrophyte remains. Pigment concentrations and chironomid head capsule counts were also very low. These facies are composed of very fine plastic sediments with some faintly laminated intervals and an organic matter composition gradually decreasing towards the top of the zone. A sharp change occurs at 25 cm (ca. ad 1940) showing a strong increase in organic matter content, algal nutrients and plant pigments together with a change in the chironomid assemblages. This might document a change in the trophic condition of the lake associated with changes in erosion/deposition rates. Although there are records of human impact in the area studied, involving the use of fires, most of the observed chemical and biological changes in Lake Hess sediment sequence were interpreted in terms of climate changes, especially to changes in moisture balance brought about by variations in the strength of the westerlies. Guest editors: K. Buczkó, J. Korponai, J. Padisák & S. W. Starratt Palaeolimnological Proxies as Tools of Environmental Reconstruction in Fresh Water     

The impact of ice melting on bacterioplankton in the Arctic Ocean

Global warming and the associated ice melt are leading to an increase in the organic carbon in the Arctic Ocean. We evaluated the effects of ice melt on bacterioplankton at 21 stations in the Greenland Sea and Arctic Ocean in the summer of 2007, when a historical minimum of Arctic ice coverage was measured. Polar Surface Waters, which have a low temperature and low salinity and originate mainly from melted ice, contained a very low abundance of bacteria (7.01 × 10⁵ ± 2.20 × 10⁵ cells ml⁻¹); however, these bacteria had high specific bacterial production (2.40 ± 1.61 fmol C bac⁻¹ d⁻¹) compared to those in Atlantic Waters. Specifically, bacterioplankton in Polar Surface Waters showed a preference for utilizing carbohydrates and had significantly higher specific activities of the glycosidases assayed, i.e. β-glucosidase, xylosidase, arabinosidase and cellobiosidase. Furthermore, bacterioplankton in Polar Sea Waters showed preferential growth on some of the carbohydrates in the Biolog Ecoplate, such as d-cellobiose and N-acetyl-d-glucosamine. Our results suggest that climate change and the associated melting of Arctic ice might induce changes in bacterioplankton functional diversity by enhancing the turnover of carbohydrates. Since organic aggregates are largely composed of polysaccharides, higher solubilization of aggregates might modify the carbon cycle, weaken the biological pump and have biogeochemical and ecological implications for the future Arctic Ocean.     

Seasonal and annual variations in biological regime of lakes in an ultracontinental climate (Trans-Baikal Region of U.S.S.R)

Summary The lakes are covered 7 months with ice, but under the transparent ice (up to 180 cm thickness) a rich vegetation of phytoplankton, phytomicrobenthos and macrophyta develop and activate the bacterial and animal population. Winter production of the phytoplankton reaches 36 g/m² C and that of the phytomicrobenthos 70 g/m² C.The water levels of the lakes show fluctuations with an amplitude of 2–4 m, affecting the whole trophic system inclusive species composition, proportion and abundance of individual aquatic organisms as well as related abiotic conditions.Co-authors: E. I. Bondereva, T. N. Morozova, (primary production), A. A. Topolov, K. A. Shishkina (microbiology), V. P. Gorlachov (zooplankton), I. M. Shapovalova (zoobenthos), N. M. Pronin (fish and their parasites), V. N. Kuzmich (nutrition of fish).Co-authors: E. I. Bondereva, T. N. Morozova, (primary production), A. A. Topolov, K. A. Shishkina (microbiology), V. P. Gorlachov (zooplankton), I. M. Shapovalova (zoobenthos), N. M. Pronin (fish and their parasites), V. N. Kuzmich (nutrition of fish).     

Public health: Climate change and infectious diseases in North America: the road ahead

Global climate change is inevitable — the combustion of fossil fuels has resulted in a buildup of greenhouse gases within the atmosphere, causing unprecedented changes to the earth''s climate. The Fourth Assessment Report of the Intergovernmental Panel on Climate Change suggests that North America will experience marked changes in weather patterns in coming decades, including warmer temperatures and increased rainfall, summertime droughts and extreme weather events (e.g., tornadoes and hurricanes). Although these events may have direct consequences for health (e.g., injuries and displacement of populations due to thermal stress), they are also likely to cause important changes in the incidence and distribution of infectious diseases, including vector-borne and zoonotic diseases, water-and food-borne diseases and diseases with environmental reservoirs (e.g., endemic fungal diseases). Changes in weather patterns and ecosystems, and health consequences of climate change will probably be most severe in far northern regions (e.g., the Arctic). We provide an overview of the expected nature and direction of such changes, which pose current and future challenges to health care providers and public health agencies.Human activities have caused a sharp increase in greenhouse gases, including carbon dioxide, nitrous oxide and methane, in the atmosphere, which has led to unprecedented changes in the earth''s climate. The Intergovernmental Panel on Climate Change was established by the United Nations Environment Program and the World Meteorological Organization in 1988 to provide objective analysis of data related to climate change. The panel comprises scientists from around the globe and aims to present the scientific, technical and socioeconomic issues arising from the data to government decision-makers in a policy-neutral context.In April 2007, the panel issued a report on the impact of global climate change on human and animal populations.¹ This report was based on about 30 000 observations of changes in physical and biological systems worldwide. More than 90% of these changes are attributable to human activities such as the combustion of fossil fuels.^1,2 The panel''s fourth assessment report includes projections for regions including North America. These projections include warmer temperatures (Figure 1), more rainfall because of an increased fraction of precipitation falling as rain rather than snow, and more frequent droughts, wildfires and extreme weather events such as hurricanes and tornados.¹ Warming is predicted to be most severe in the northernmost latitudes.Open in a separate windowFigure 1: Trends in mean global temperatures since the mid-19th century. Coloured lines represent the linear trends over various time periods. Shorter (more recent time periods) lines have steeper slopes, indicating an accelerating warming trend for the planet. Reproduced, with permission, from reference 2. Copyright 2007 Cambridge University Press.Some of the health effects attributable to climate change are directly related to changing environmental conditions. The Public Health Agency of Canada anticipates increased burden of disease as a result of thermal stress and more frequent extreme weather events,³ and some projected direct effects of climate change on human health, such as heat-related morbidity and injuries, have been previously reviewed.⁴ However, climate and weather patterns are important physical components of complex ecosystems⁵ and any major change in the nonliving component of an ecosystem will affect living components, including microbes, insect vectors, animal reservoirs and susceptible humans, and change the incidence and distribution of infectious diseases.The close relation between climate, environment and infectious disease in the developing world are well recognized. For example, the importance of rainfall and drought in the occurrence of malaria,^6,7 the influence of the dry season on epidemic meningococcal disease in the sub-Saharan African “meningitis belt”⁸ and the importance of warm ocean waters in driving cholera occurrence in the Ganges River delta and elsewhere in Asia⁹ are well described. Indeed, there is widespread concern about the potential impact of global climate change on the distribution and burden of these and other infectious threats in the developing world.^1,7The relation between ecosystems, infectious diseases and global climate change are less intuitive in the context of more developed countries where clean drinking water, reduced exposure to insect vectors, higher-quality housing and other advantages partly mitigate such threats. However, climate changes projected to occur in the coming decades are likely to influence the burden and incidence of infectious diseases in more developed regions including North America. In this review, we describe the nature and direction of changes in infectious disease epidemiology that are likely to accompany global climate change and describe the challenges that these changes will pose to health care providers and public health agencies. We focus principally on Canada and the United States, including the Arctic regions of North America, where the effects of global climate change are likely to be most severe. We also include several illustrative examples from other highly developed regions such as the European Union and Australia. In particular, we review several zoonotic diseases of public health importance, the association between precipitation and water-borne diarrheal diseases, seasonal respiratory diseases with person-to-person transmission and endemic mycoses (Open in a separate windowThis review is not meant to obscure the likelihood that the brunt of the increased incidence of infectious diseases related to climate change will occur in the same less-developed, economically poor countries that are currently most affected by infectious diseases.^1,10 For more information about the projected changes in infectious disease epidemiology in these diverse regions of the world, we encourage readers to consult the panel report and other reports and reviews devoted to this topic.^1,7,11,12     

Regression-based age estimation of a stratigraphic isotope sequence in Switzerland

Multi-proxy data such as pollen percentages, aquatic biota, and stable isotope ratios in lake sediments in conjunction with climate transfer functions can be used to reconstruct past climate. This has been the subject of some recent projects. Often, stable-isotope ratios of oxygen are used as an independent proxy for climate. Past climate so reconstructed can in turn be used to assess the response of past vegetation to climatic oscillations, for instance near the epoch boundaries. One important intermediate step is to establish the age of the stratigraphic sequence. Strong similarities between the δ ¹⁸O records from European lake sediments and the Greenland ice cores are of interest. The Greenland ice-core project (GRIP) provided δ ¹⁸O data that were dated using an ice-flow model. Although the physical laws behind the isotope series from ice and lake sediment are different, statistical methods can be used to match the two series. In this paper, a regression-based approach is suggested for series matching. The method is illustrated by analyzing a series of δ ¹⁸O records covering the Late-glacial interstadial (ca. 15,000–13,000 years b.p. [1950]) from Gerzensee, Switzerland. Regression methods for age-depth modelling have also been recommended by other authors. Such an approach leads to reproducible and statistically founded age estimates and can easily be updated to include new data and information as needed. In this paper, the modelling step is preceded by identifying comparable sub-sections in the two isotope series by empirically matching the local minima and maxima in the smoothed isotope values; regression models are then used locally for each sub-section. This accommodates for local differences in the parameters. Variations in the final age estimates caused by different choices of the smoothing (bandwidth) parameters used in the intermediate nonparametric smoothing step are also taken into account in this algorithm.     

Sea ice seasonality during the Holocene, Adélie Land, East Antarctica

Thin sections of laminated cores from different Antarctic coastal areas have demonstrated the potential of diatom species to document climate change at the seasonal scale. Here we present the relative abundances of four diatom species and species groups (Fragilariopsis curta group as a proxy for yearly sea ice cover, F. kerguelensis as a proxy for summer sea-surface temperature, Chaetoceros Hyalochaete resting spores as a proxy for spring sea ice melting and the Thalassiosira antarctica group as a proxy for autumn sea ice formation) in core MD03-2601 retrieved off Adélie Land on the Antarctic continental shelf. These abundances were compared to surface temperatures and sea ice cover modelled over the last 9000 years. Both the marine records and the simulated climate demonstrated a cooler Early Holocene (9000–7700 years BP), a warmer Mid-Holocene (7700–4000 years BP) and a colder Late Holocene (4000–1000 years BP). Yearly sea ice cover followed an inverse pattern to temperatures with less sea ice during the Mid-Holocene Hypsithermal than during the Late Holocene Neoglacial. However, diatom census counts and model output indicate that sea ice spring melting happened earlier in the season, as expected, but that autumn sea ice formation also occurred earlier in the season during the Hypsithermal than during the colder Neoglacial, thereby following seasonal changes in local insolation.     

Growing Season Temperatures in Europe and Climate Forcings Over the Past 1400 Years

Background

The lack of instrumental data before the mid-19th-century limits our understanding of present warming trends. In the absence of direct measurements, we used proxies that are natural or historical archives recording past climatic changes. A gridded reconstruction of spring-summer temperature was produced for Europe based on tree-rings, documentaries, pollen assemblages and ice cores. The majority of proxy series have an annual resolution. For a better inference of long-term climate variation, they were completed by low-resolution data (decadal or more), mostly on pollen and ice-core data.

Methodology/Principal Findings

An original spectral analog method was devised to deal with this heterogeneous dataset, and to preserve long-term variations and the variability of temperature series. So we can replace the recent climate changes in a broader context of the past 1400 years. This preservation is possible because the method is not based on a calibration (regression) but on similarities between assemblages of proxies. The reconstruction of the April-September temperatures was validated with a Jack-knife technique. It was also compared to other spatially gridded temperature reconstructions, literature data, and glacier advance and retreat curves. We also attempted to relate the spatial distribution of European temperature anomalies to known solar and volcanic forcings.

Conclusions

We found that our results were accurate back to 750. Cold periods prior to the 20^th century can be explained partly by low solar activity and/or high volcanic activity. The Medieval Warm Period (MWP) could be correlated to higher solar activity. During the 20^th century, however only anthropogenic forcing can explain the exceptionally high temperature rise. Warm periods of the Middle Age were spatially more heterogeneous than last decades, and then locally it could have been warmer. However, at the continental scale, the last decades were clearly warmer than any period of the last 1400 years. The heterogeneity of MWP versus the homogeneity of the last decades is likely an argument that different forcings could have operated. These results support the fact that we are living a climate change in Europe never seen in the past 1400 years.     

Digest: Climate plays marginal role for homomorphic sex chromosome differentiation in common frogs†

In systems with early stage sex-chromosome evolution, climate gradients can largely explain changes in the sex-determining systems (i.e., genetic or environmental factors). However, in the common frog Rana temporaria, Phillips et al. found that phylogeography, rather than elevation (used as a proxy for climate), was associated with homomorphic sex-chromosome differentiation levels.     

Modeling Cumulative Effects of Climate and Development on Moose,Wolf, and Caribou Populations

Wildlife models focused solely on a single strong influence (e.g., habitat components, wildlife harvest) are limited in their ability to detect key mechanisms influencing population change. Instead, we propose integrated modeling in the context of cumulative effects assessment using multispecies population dynamics models linked to landscape-climate simulation at large spatial and temporal scales. We developed an integrated landscape and population simulation model using ALCES Online as the model-building platform, and the model accounted for key ecological components and relationships among moose (Alces alces), grey wolves (Canis lupus nubilus), and woodland caribou (Rangifer tarandus caribou) in northern Ontario, Canada. We simulated multiple scenarios over 5 decades (beginning 2020) to explore sensitivity to climate change and land use and assessed effects at multiple scales. The magnitude of effect and the relative importance of key factors (climate change, roads, and habitat) differed depending on the scale of assessment. Across the full extent of the study area (654,311km² [ecozonal scale]), the caribou population declined by 26% largely because of climate change and associated predator-prey response, which led to caribou range recession in the southern part of the study area. At the caribou range scale (108,378 km²), which focused on 2 herds in the northern part of the study area, climate change led to a 10% decline in the population and development led to an additional 7% decline. At the project scale (8,331 km²), which was focused more narrowly on the landscape surrounding 4 proposed mines, the caribou population declined by 29% largely in response to simulated development. Given that observed caribou population dynamics were sensitive to the cumulative effects of climate change, land use, interspecific interactions, and scale, insights from the analysis might not emerge under a less complex model. Our integrated modeling framework provides valuable support for broader regional assessments, including estimation of risk to caribou and Indigenous food security, and for developing and evaluating potential caribou recovery strategies. © 2021 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society.     

Lake-based climate reconstruction in Africa: progress and challenges

Lake sediments are and will continue to be the principal source of information on the climate history of tropical Africa. However, unequivocal interpretation of the various sedimentological, biological, and geochemical climate-proxy data extracted from lake sediments with respect to past variations in temperature, rainfall, and wind is an extremely complex and challenging exercise. Outstanding problems are: (1) the inherent conflict between a lake's sensitivity to climate change (its ability to respond to and record relatively modest, short-lived climatic anomalies) and its persistence as an archive of climate change (the probability that it survived the most arid events without desiccation or erosion, allowing it to preserve a continuous record of climate history); (2) the scarcity of annually laminated sediment records, which in other regions can provide superior chronological precision to lake-based climate reconstructions; (3) lack of a quantitative (sometimes even qualitative) mechanistic understanding of the chain of cause and effect linking sedimentary climate-proxy indicators to particular climatic variables; and (4) lack of a proxy indicator for past temperature changes unaffected by simultaneous changes in moisture balance. Clearly, a climate-proxy record with high stratigraphic resolution does not represent a high-resolution record of past climate change without demonstration that the sedimentary archive is continuous and undisturbed; that the lake system responds to climate variability at the appropriate time scale; and that any threshold effects in the relationship between the proxy indicator and climate are accounted for. Calibration and validation of climate-proxy indicators is tantamount to establishing accurate reconstructions, but in Africa historical validation of proxy indicators is handicapped by the scarcity of long-term lake-monitoring data. The reliability of lake-based climate reconstructions is enhanced when inferences derived from several proxy indicators (sedimentological, biological, or geochemical), that each have an independent mechanistic link to climate, show a high level of coherence. Given the scarcity of annually-resolved sediment records in tropical Africa, we may have to accept the limitations of ²¹⁰Pb- and ¹⁴C-based chronologies when evaluating the synchrony of reconstructed climate events between sites and regions; however, careful site selection and detailed lithostratigraphic analyses can go a long way to optimise depth-age models and reduce uncertainty in the timing of past climate changes.     

青藏高原植被生态系统垂直分布变化的情景模拟

如何模拟和揭示青藏高原植被生态系统垂直分布在全球气候变化驱动下的时空变化情景,对定量解析青藏高原陆地生态系统对气候变化响应效应具有重要意义。该论文基于Holdridge life zone （HLZ）模型,结合数字高程模型（DEM）数据,改变模型输入参数模式,发展了改进型HLZ生态系统模型。结合1981-2010（T0）时段的气候观测数据和IPCC CMIP5 RCP2.6、RCP4.5、RCP8.5三种情景2011-2040（T1）、2041-2070（T2）、2071-2100（T3）三个时段气候情景数据,实现了青藏高原植被生态系统垂直分布的时空变化情景模拟。引入生态系统平均中心时空偏移趋势模型和生态多样性指数模型,定量揭示了青藏高原植被生态系统在不同垂直带上的时空变化情景。结果显示：青藏高原共有16种植被生态系统类型;冰雪/冰原、高山潮湿苔原和亚高山湿润森林为青藏高原主要的植被生态系统类型,其面积之和占到了青藏高原总面积的56.26%;高山干苔原、亚高山潮湿森林、山地灌丛、山地湿润森林和荒漠等对气候变化的敏感性总体上高于其它类型;在T0-T3期间,青藏高原的高山湿润苔原、高山干苔原、荒漠呈持续减少趋势,平均每10年将分别减少1.96×10⁴km²、0.15×10⁴km²和1.58×10⁴km²;亚高山潮湿森林、山地湿润森林和山地灌丛呈持续增加趋势,平均每10年将分别增加3.42×10⁴km²、2.98×10⁴km²和1.19×10⁴km²;RCP8.5情景下青藏高原的植被生态系统平均中心的偏移幅度最大,RCP4.5情景下的偏移幅度次之,而RCP2.6情景下的偏移幅度最小。另外,在三种气候变化情景驱动下,青藏高原植被生态系统的生态多样性呈减少趋势。总之,未来不同情景的气候变化将直接影响青藏高原植被生态系统的时空分布格局及其生态多样性,气候变化强度越高,影响就越大,而且气候变化对青藏高原植被生态系统的影响呈现出从低海拔到高海拔递增的影响效应。     

Climate reconstructions and monitoring in the Mediterranean Sea: A review on some recently discovered high-resolution marine archives

Palaeoclimate records are important tools for understanding climate modifications and contextualizing recent anthropogenic perturbations in climate change relative to natural variability in the Earthclimate system. Moreover, time-series proxy records of the main physical and chemical parameters in marine and continental environments are increasingly used for testing climate models in order to ascertain the reliability of projections for future scenarios in our greenhouse modified Earth. In order to account for the limited number of continuous instrumental measurements of climatic variables in the past, such as sea surface temperature (SST), salinity (SSS), sea-level fluctuations and water chemistry, a complementary approach is the examination of geochemical tracers (i.e. trace elements and stable isotopes) in well-dated natural marine archives. Recently, the Mediterranean Sea has been the focus of a number of studies where new high resolution climate archives have been investigated utilizing proxies for sea surface temperature, salinity,marine chemistry, and ocean circulation, different to those available for tropical regions. In particular, vermetids (Dendropoma petraeum), non-tropical zooxanthellate corals (Cladocora caespitosa) and cold-water corals (Desmophyllum dianthus, Lophelia pertusa and Madrepora oculata) have been studied by conventional and advanced analytical techniques (e.g., laser ablation ICP-MS, MC-ICP-MS, synchrotron X-ray fluorescence) and have been successfully used as high-resolution palaeoenvironmental proxies. Vermetid reefs have the potential to yield valuable information on past sea-level changes and SST, through the combination of stable isotopes and radiocarbon dating. The trace element concentration, in combination with U-series and radiocarbon dating, of the skeletal aragonite of the Mediterranean zooxanthellate coral Cladocora caespitosa, and of the coldwater corals Desmophyllum dianthus and Lophelia pertusa, has been successfully demonstrated to be a valid high-resolution SST archive, and a seawater chemistry and ocean circulation proxy, respectively. Here we present a review of our research over the last few years, aiming for the establishment of new natural marine archives collected from various sites of the Mediterranean Sea, reporting on our methodological approaches and main results.      

Response of Glacier and Lake Dynamics in Four Inland Basins to Climate Change at the Transition Zone between the Karakorum And Himalayas

Inland glacier and lake dynamics on the Tibetan Plateau (TP) and its surroundings over recent decades are good indicators of climate change and have a significant impact on the local water supply and ecosystem. The glacier and lake changes in Karakoram are quite different from those of the Himalayas. The mechanisms of the complex and regionally heterogeneous behavior of the glacier and lake changes between the Karakorum and Himalayas are poorly understood. Based on satellite images and meteorological data of Shiquanhe, Hetian, and Yutian stations, we demonstrate that the overall retreat of glaciers and increase of lake area at the transition zone between the Karakoram and Himalayas (TKH) have occurred since 1968 in response to a significant global climate change. Glacial areas in the Songmuxi Co basin, Zepu Co basin, Mang Co basin and Unnamed Co decreased by -1.98 ± 0.02 km², -5.39 ± 0.02 km², -0.01 ± 0.02 km², and -0.12 ± 0.02 km² during the study period, corresponding to losses of -1.42%, -2.86%, -1.54%, and -1.57%, respectively. The lake area of the Songmuxi Co, Zepu Co, Mang Co and Unnamed Co increased by 7.57 ± 0.02 km², 8.53 ± 0.02 km², 1.35 ± 0.02 km², and 0.53±0.02 km², corresponding to growths of 30.22%, 7.55%, 11.39%, and 8.05%, respectively. Increases in temperature was the main reason for glacier retreat, whereas decreases in potential evapotranspiration of lakes, increases in precipitation, and increases in melt water from glaciers and frozen soil all contributed to lake area expansion.     

Soil Microbial Community Responses to Multiple Experimental Climate Change Drivers

Researchers agree that climate change factors such as rising atmospheric [CO₂] and warming will likely interact to modify ecosystem properties and processes. However, the response of the microbial communities that regulate ecosystem processes is less predictable. We measured the direct and interactive effects of climatic change on soil fungal and bacterial communities (abundance and composition) in a multifactor climate change experiment that exposed a constructed old-field ecosystem to different atmospheric CO₂ concentration (ambient, +300 ppm), temperature (ambient, +3°C), and precipitation (wet and dry) might interact to alter soil bacterial and fungal abundance and community structure in an old-field ecosystem. We found that (i) fungal abundance increased in warmed treatments; (ii) bacterial abundance increased in warmed plots with elevated atmospheric [CO₂] but decreased in warmed plots under ambient atmospheric [CO₂]; (iii) the phylogenetic distribution of bacterial and fungal clones and their relative abundance varied among treatments, as indicated by changes in 16S rRNA and 28S rRNA genes; (iv) changes in precipitation altered the relative abundance of Proteobacteria and Acidobacteria, where Acidobacteria decreased with a concomitant increase in the Proteobacteria in wet relative to dry treatments; and (v) changes in precipitation altered fungal community composition, primarily through lineage specific changes within a recently discovered group known as soil clone group I. Taken together, our results indicate that climate change drivers and their interactions may cause changes in bacterial and fungal overall abundance; however, changes in precipitation tended to have a much greater effect on the community composition. These results illustrate the potential for complex community changes in terrestrial ecosystems under climate change scenarios that alter multiple factors simultaneously.Soil microbial communities are responsible for the cycling of carbon (C) and nutrients in ecosystems, and their activities are regulated by biotic and abiotic factors such as the quantity and quality of litter inputs, temperature, and moisture. Atmospheric and climatic changes will impact both abiotic and biotic drivers in ecosystems and the response of ecosystems to these changes. Feedbacks from ecosystem to the atmosphere may also be regulated by soil microbial communities (3). Although microbial communities regulate important ecosystem processes, it is often unclear how the abundance and composition of microbial communities correlate with climatic perturbations and interact to effect ecosystem processes. As such, much of the ecosystem climate change research conducted to date has focused on macroscale responses to climatic change such as changes in plant growth (43, 44), plant community composition (2, 37), and coarse scale soil processes (14, 18, 21, 26), many of which may also indirectly interact to effect microbial processes. Studies that have addressed the role of microbial communities and processes have most often targeted gross parameters, such as microbial biomass, enzymatic activity, or basic microbial community profiles in response to single climate change factors (22, 28, 29, 33, 61, 63).Climate change factors such as atmospheric CO₂ concentrations, warming, and altered precipitation regimes can potentially have both direct and indirect impacts on soil microbial communities. However, the direction and magnitude of these responses is uncertain. For example, the response of soil microbial communities to changes in atmospheric CO₂ concentrations can be positive or negative, and consistent overall trends between sites and studies have not been observed (1, 28, 34-36). Further, depending on what limits ecosystem productivity, precipitation and soil moisture changes may increase or decrease the ratio of bacteria and fungi, as well as shift their community composition (8, 50, 58). Increasing temperatures can increase in microbial activity, processing, and turnover, causing the microbial community to shift in favor of representatives adapted to higher temperatures and faster growth rates (7, 46, 60, 64, 65). Atmospheric and climatic changes are happening in concert with one another so that ecosystems are experiencing higher levels of atmospheric CO₂, warming, and changes in precipitation regimes simultaneously. Although the many single factor climate change studies described above have enabled a better understanding of how microbial communities may respond to any one factor, understanding how multiple climate change factors interact with each other to influence microbial community responses is poorly understood. For example, elevated atmospheric [CO₂] and precipitation changes might increase soil moisture in an ecosystem, but this increase may be counteracted by warming (10). Similarly, warming may increase microbial activity in an ecosystem, but this increase may be eliminated if changes in precipitation lead to a drier soil condition or reduced litter quantity, quality, and turnover. Such interactive effects of climate factors in a multifactorial context have been less commonly studied even in plant communities (45), and detailed studies are rarer still in soil microbial communities (25). Clearly, understanding how microbial communities will respond to these atmospheric and climate change drivers is important to make accurate predications of how ecosystems may respond to future climate scenarios.To address how multiple climate change drivers will interact to shape soil microbial communities, we took advantage of a multifactor climatic change experiment that manipulated atmospheric CO₂ (+300 ppm, ambient), warming (+3°C, ambient) and precipitation (wet and dry) in a constructed old-field ecosystem that had been ongoing for 3.5 years at the time of sampling. Previous work on this project has demonstrated direct and interactive effects of the treatments on plant community composition and biomass (15, 30), soil respiration (56), microbial activity (30), nitrogen fixation (21), and soil carbon stocks (20). These results led us to investigations of how the soil bacterial and fungal communities, important regulators of some of these processes, were responding using culture-independent molecular approaches. Our research addresses two overarching questions. (i) Do climatic change factors and their interactions alter bacterial and fungal abundance and diversity? (ii) Do climatic change factors and their interactions alter bacterial or fungal community composition?     

Paleolimnological reconstruction of the trophic state in Lake Balaton (Hungary) using Cladocera remains

The sediment of Lake Balaton (Hungary) provides important information about the lake’s history, particularly with regard to eutrophication. In this study, we used fossil pigment analysis and subfossil Cladocera remains preserved in a dated sediment core to identify trophic stages from ~250 bc to present. Dates of the most recent eutrophic events are in good agreement with previously published data. In general, the abundance and diversity of the Cladocera community increased with eutrophication and decreased with oligotrophication. The sediments of Lake Balaton were characterised by Chydoridae remains, of which Alona species were the most abundant. Of these, Alona quadrangularis and Alona affinis accounted for 40 and 20% of the total Cladocera remains, respectively. The trophic state of Lake Balaton varied between mesotrophic and eutrophic regimes. Seven different trophic periods were identified in Lake Balaton on the basis of Sedimentary Pigment Degradation Unit (SPDU) content of the sediment. Eutrophic states were (1) from ~250 to ~30 bc, (3) between ~300 and ~590 ad, (5) between 1834 and 1944 and (7) from the 1960s until present. Mesotrophic states were (2) ~30 bc to ~300 ad, (4) 590–1834, (6) 1944–1960s. Discriminant analysis of the cladoceran data confirmed these historic events, except for the short mesotrophic episode between 1944 and 1960. The first stage of eutrophication of Lake Balaton (~250 to ~30 bc) was characterised by extensive macrophyte vegetation, as indicated by the increasing abundance of vegetation-associated Cladocera species (Eurycercus lamellatus, Sida crystallina, Pleuroxus sp.). Intensification of eutrophication was identified since the 1980s, reflected by a high abundance of Bosmina species. The most significant planktivorous fish of Lake Balaton was the Sabre carp (Pelecus cultratus), and when its number decreased, the abundance of Bosmina species increased. This study shows that Cladocera are responsive to trophic state changes, underlining their importance as a tool for the assessment of lake eutrophication.     

Two Challenges for U.S. Irrigation Due to Climate Change: Increasing Irrigated Area in Wet States and Increasing Irrigation Rates in Dry States

Agricultural irrigation practices will likely be affected by climate change. In this paper, we use a statistical model relating observed water use by U.S. producers to the moisture deficit, and then use this statistical model to project climate changes impact on both the fraction of agricultural land irrigated and the irrigation rate (m³ha⁻¹). Data on water withdrawals for US states (1985–2005) show that both quantities are highly positively correlated with moisture deficit (precipitation – PET). If current trends hold, climate change would increase agricultural demand for irrigation in 2090 by 4.5–21.9 million ha (B1 scenario demand: 4.5–8.7 million ha, A2 scenario demand: 9.1–21.9 million ha). Much of this new irrigated area would occur in states that currently have a wet climate and a small fraction of their agricultural land currently irrigated, posing a challenge to policymakers in states with less experience with strict regulation of agriculture water use. Moreover, most of this expansion will occur in states where current agricultural production has relatively low market value per hectare, which may make installation of irrigation uneconomical without significant changes in crops or practices by producers. Without significant increases in irrigation efficiency, climate change would also increase the average irrigation rate from 7,963 to 8,400–10,415 m³ha⁻¹ (B1 rate: 8,400–9,145 m³ha⁻¹, A2 rate: 9,380–10,415 m³ha⁻¹). The irrigation rate will increase the most in states that already have dry climates and large irrigation rates, posing a challenge for water supply systems in these states. Accounting for both the increase in irrigated area and irrigation rate, total withdrawals might increase by 47.7–283.4 billion m³ (B1 withdrawal: 47.7–106.0 billion m³, A2 withdrawal: 117.4–283.4 billion m³). Increases in irrigation water-use efficiency, particularly by reducing the prevalence of surface irrigation, could eliminate the increase in total irrigation withdrawals in many states.     

美味猕猴桃地理分布模拟与气候变化影响分析

为了解气候变化对美味猕猴桃(Actinidia deliciosa)地理分布的影响,结合气候情景,采用Maxent预测美味猕猴桃的适生区的变化趋势。结果表明,基准气候和未来情景下构建的美味猕猴桃分布模型的AUC值均达到极好的标准。基准气候条件下,美味猕猴桃在中国的适生区为22°~38°N,96°~122°E,总面积为3.367 9×106 km2,高适生区位于秦岭-巴山、四川盆地东部、云贵高原东部、武陵山-巫山、武夷山脉。RCP4.5和RCP8.5情景下,美味猕猴桃在中国的高适生区面积将显著减少,中适生区面积则呈增加趋势,两种情景下高、中质心均向偏南或低纬度方向移动,RCP8.5情景下质心的迁移轨迹最长,变动范围最大。Maxent模型的准确预测对于优化猕猴桃产业结构具有重要指导意义。     

X-ray microdensitometry applied to subfossil tree-rings: growth characteristics of ancient pines from the southern boreal forest zone in Finland at intra-annual to centennial time-scales

A collection of subfossil wood of Pinus sylvestris (Scots pine) was exposed to X-ray densitometry. The collection of 64 samples from the southern boreal forest zone was dendrochronologically cross-dated to a.d. 673-1788. Growth characteristics were determined by performing density profiles including the following parameters: minimum density, earlywood and latewood boundary density, maximum density, earlywood width, earlywood density, latewood width, latewood density, annual ring width and annual ring density. Seven out of the nine parameters were found to contain non-climatic growth trends and six were found to be heteroscedastic in their variance. Tree-specific records were indexed, to remove the non-climatic growth trends and stabilize the variance, and combined into nine parameter-specific tree-ring chronologies. Growth characteristics of the pines changed in parallel with the generally agreed climatic cooling from the Medieval Warm Period to the Little Ice Age: pine tree-rings showed decreasing maximum densities from the period a.d. 975-1150 to a.d. 1450–1625. A concomitant change in the intra-annual growth characteristics was detected between these periods. The findings indicate that not only the trees growing near the species’ distributional limits are sensitive to large-scale climatic variations but also the trees growing in habitats remote from the timberline have noticeably responded to past climate changes.