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

Multiple-source heterotrophy fueled by aged organic carbon in an urbanized estuary

Natural lakes and reservoirs are important, yet not well constrained sources of greenhouse gasses to the atmosphere. In particular for N2O emissions, a huge variability is observed in the few, obse ...

Natural Lakes Are a Minor Global Source of N2O to the Atmosphere

Temperature versus hydrologic controls of chemical weathering fluxes from United States forests

Understanding the processes controlling the transfer of organic matter from terrestrial to aquatic ecosystems is of fundamental importance for the aquatic sciences. Over the course of a full year, fluorescence, absorbance and bioavailability of dissolved organic matter (DOM) were characterised in Bigelow Brook, a forested headwater stream in Massachusetts, USA. Parallel factor analysis (PARAFAC) identified a four-component model to describe observed DOM fluorescence (C1–C4). Component C2 exhibited the characteristics of a more humic-like fluorophore, with a potentially more reduced redox state and increased with discharge, whereas more fulvic-like (C1) and protein-like (C3, C4) fluorophores decreased. Under both dark and light-exposed conditions, percentage bioavailable dissolved organic carbon (%BDOC) increased with discharge (R2 = 0.37 and R2 = 0.56). C2 and specific absorptivity (SUVA) were reduced following BDOC incubations, whereas C1, C3 and C4 increased. These changes to DOM characteristics with increasing discharge were observed under both baseflow and stormflow conditions, indicating that with rising watertable, loading from a large riparian or hyporheic pool of organic matter is likely occurring. Other headwater streams, where loading is controlled by hillslope processes, are likely to exhibit a similar pattern of increasing export of more humic and bioavailable DOM during hydrologic events.

Increases in humic and bioavailable dissolved organic matter in a forested New England headwater stream with increasing discharge

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018JG004750

Peter A. Raymond

Papers

Multiple-source heterotrophy fueled by aged organic carbon in an urbanized estuary

Natural Lakes Are a Minor Global Source of N2O to the Atmosphere

Temperature versus hydrologic controls of chemical weathering fluxes from United States forests

Increases in humic and bioavailable dissolved organic matter in a forested New England headwater stream with increasing discharge

Differential Response of Greenhouse Gas Evasion to Storms in Forested and Wetland Streams