抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Globally, soil organic matter (SOM) contains more than three times as much carbon as either the atmosphere or terrestrial vegetation. Yet it remains largely unknown why some SOM persists for millennia whereas other SOM decomposes readily—and this limits our ability to predict how soils will respond to climate change. Recent analytical and experimental advances have demonstrated that molecular structure alone does not control SOM stability: in fact, environmental and biological controls predominate. Here we propose ways to include this understanding in a new generation of experiments and soil carbon models, thereby improving predictions of the SOM response to global warming.

/pdf/persistence-of-soil-organic-matter-as-an-ecosystem-property-ago0khy192.pdf

Persistence of soil organic matter as an ecosystem property

Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

/pdf/climate-change-2007-the-physical-science-basis-1x93ttz9jt.pdf

Climate Change 2007: The Physical Science Basis.

Human alteration of the global environment has triggered the sixth major extinction event in the history of life and caused widespread changes in the global distribution of organisms. These changes in biodiversity alter ecosystem processes and change the resilience of ecosystems to environmental change. This has profound consequences for services that humans derive from ecosystems. The large ecological and societal consequences of changing biodiversity should be minimized to preserve options for future solutions to global environmental problems.

Consequences of changing biodiversity

Because freshwater covers such a small fraction of the Earth’s surface area, inland freshwater ecosystems (particularly lakes, rivers, and reservoirs) have rarely been considered as potentially important quantitative components of the carbon cycle at either global or regional scales. By taking published estimates of gas exchange, sediment accumulation, and carbon transport for a variety of aquatic systems, we have constructed a budget for the role of inland water ecosystems in the global carbon cycle. Our analysis conservatively estimates that inland waters annually receive, from a combination of background and anthropogenically altered sources, on the order of 1.9 Pg C y−1 from the terrestrial landscape, of which about 0.2 is buried in aquatic sediments, at least 0.8 (possibly much more) is returned to the atmosphere as gas exchange while the remaining 0.9 Pg y−1 is delivered to the oceans, roughly equally as inorganic and organic carbon. Thus, roughly twice as much C enters inland aquatic systems from land as is exported from land to the sea. Over prolonged time net carbon fluxes in aquatic systems tend to be greater per unit area than in much of the surrounding land. Although their area is small, these freshwater aquatic systems can affect regional C balances. Further, the inclusion of inland, freshwater ecosystems provides useful insight about the storage, oxidation and transport of terrestrial C, and may warrant a revision of how the modern net C sink on land is described.

/pdf/plumbing-the-global-carbon-cycle-integrating-inland-waters-1enndt5kqx.pdf

Plumbing the Global Carbon Cycle: Integrating Inland Waters into the Terrestrial Carbon Budget

Ecological theory emphasizes headwater streams and wetlands as hotspots for metabolism of terrestrially derived organic matter and biogeochemical transformations. Growing evidence indicates that freshwater ecosystems may be as important as terrestrial and marine environments in the annual flux of CO2 to the atmosphere. The National Ecological Observatory Network (NEON) and the Stream Ecological Observatory Network (STREON) offer the opportunity to collect and analyze data related to these processes at spatial scales ranging from local to continental and at temporal scales from minutes to millennia. These data can be used to understand how global climate change and subsequent shifts in terrestrial plant communities and precipitation regimes will influence the export and composition of dissolved organic matter (DOM) to headwater streams, downstream freshwater ecosystems, and coastal environments. Moreover, temporal scaling of DOM export among watersheds is an underexploited frontier research area th...

https://www.jstor.org/stable/10.1086/679747

Watershed hydrology and dissolved organic matter export across time scales: minute to millennium

Background There has been a dramatic increase in the incidence of sporadic legionnaires' disease in Connecticut since 1999, but the exact reasons for this are unknown. Therefore, there is a growing need to understand the drivers of legionnaires' disease in the community. In this study, we explored the relationship between the natural environment and the spatial and temporal distribution of legionellosis cases in Connecticut. Methods We used spatial models and time series methods to evaluate factors associated with the increase and clustering of legionellosis in Connecticut. Stream flow, proximity to rivers, and residence in regional watersheds were explored as novel predictors of disease, while controlling for testing intensity and correlates of urbanization. Results In Connecticut, legionellosis incidence exhibited a strong pattern of spatial clustering. Proximity to several rivers and residence in the corresponding watersheds were associated with increased incidence of the disease. Elevated rainfall and stream flow rate were associated with increases in incidence 2 weeks later. Conclusions We identified a novel relationship between the natural aquatic environment and the spatial distribution of sporadic cases of legionellosis. These results suggest that natural environmental reservoirs may have a greater influence on the spatial distribution of sporadic legionellosis cases than previously thought.

/pdf/association-between-sporadic-legionellosis-and-river-systems-4n1r1c5poh.pdf

Association Between Sporadic Legionellosis and River Systems in Connecticut.

Biogeochemical cycles in estuaries are regulated by a diverse set of physical and biological variables that operate over a variety of time scales. Using in situ optical sensors, we conducted a high-frequency time-series study of several biogeochemical parameters at a mooring in central Long Island Sound from May to August 2010. During this period, we documented well-defined diel cycles in nitrate concentration that were correlated to dissolved oxygen, wind stress, tidal mixing, and irradiance. By filtering the data to separate the nitrate time series into various signal components, we estimated the amount of variation that could be ascribed to each process. Primary production and surface wind stress explained 59 and 19 %, respectively, of the variation in nitrate concentrations. Less frequent physical forcings, including large-magnitude wind events and spring tides, served to decouple the relationship between oxygen, nitrate, and sunlight on about one quarter of study days. Daytime nitrate minima and dissolved oxygen maxima occurred nearly simultaneously on the majority (>80 %) of days during the study period; both were strongly correlated with the daily peak in irradiance. Nighttime nitrate maxima reflected a pattern in which surface-layer stocks were depleted each afternoon and recharged the following night. Changes in nitrate concentrations were used to generate daily estimates of new primary production (182 ± 37 mg C m−2 day−1) and the f ratio (0.25), i.e., the ratio of production based on nitrate to total production. These estimates, the first of their kind in Long Island Sound, were compared to values of community respiration, primary productivity, and net ecosystem metabolism, which were derived from in situ measurements of oxygen concentration. Daily averages of the three metabolic parameters were 1,660 ± 431, 2,080 ± 419, and 429 ± 203 mg C m−2 day−1, respectively. While the system remained weakly autotrophic over the duration of the study period, we observed very large day-to-day differences in the f ratio and in the various metabolic parameters.

/pdf/estimates-of-new-and-total-productivity-in-central-long-2dqbe99q83.pdf

Estimates of New and Total Productivity in Central Long Island Sound from In Situ Measurements of Nitrate and Dissolved Oxygen

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2016GL070206

Substantial overnight reaeration by convective cooling discovered in pond ecosystems

The inorganic carbon carried in rivers of the Amazon basin seems to originate largely from the decomposition of young plant material — a finding that improves our understanding of the role of rivers in the carbon cycle. Rivers and their surrounding environments have received little attention in studies addressing regional carbon budgets and global climate change. But recent evidence suggests that Amazonian rivers outgas a significant amount of carbon dioxide. An extensive geochemical survey of rivers in the Amazon basin now finds that the dominant source of carbon dioxide is the respiration of organic matter that is less than five years old, probably originating from near-stream vegetation. Although most of the organic matter transported by these rivers is tens to thousands of years old, it is this small rapidly cycling pool of organic matter that is responsible for the large carbon dioxide fluxes from the rivers to the atmosphere in the humid tropics.

Peter A. Raymond

Papers

Watershed hydrology and dissolved organic matter export across time scales: minute to millennium

Association Between Sporadic Legionellosis and River Systems in Connecticut.

Estimates of New and Total Productivity in Central Long Island Sound from In Situ Measurements of Nitrate and Dissolved Oxygen

Substantial overnight reaeration by convective cooling discovered in pond ecosystems

The age of the Amazon's breath