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

The terrestrial carbon sink has been large in recent decades, but its size and location remain uncertain. Using forest inventory data and long-term ecosystem carbon studies, we estimate a total forest sink of 2.4 ± 0.4 petagrams of carbon per year (Pg C year–1) globally for 1990 to 2007. We also estimate a source of 1.3 ± 0.7 Pg C year–1 from tropical land-use change, consisting of a gross tropical deforestation emission of 2.9 ± 0.5 Pg C year–1 partially compensated by a carbon sink in tropical forest regrowth of 1.6 ± 0.5 Pg C year–1. Together, the fluxes comprise a net global forest sink of 1.1 ± 0.8 Pg C year–1, with tropical estimates having the largest uncertainties. Our total forest sink estimate is equivalent in magnitude to the terrestrial sink deduced from fossil fuel emissions and land-use change sources minus ocean and atmospheric sinks.

/pdf/a-large-and-persistent-carbon-sink-in-the-world-s-forests-2rgrfjaqnh.pdf

A Large and Persistent Carbon Sink in the World’s Forests

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.

https://www.nrs.fs.fed.us/pubs/jrnl/2011/nrs_2011_pan_002-supporting.pdf

Supporting Online Material for A Large and Persistent Carbon Sink in the World's Forests

The continued increase in the atmospheric concentration of carbon dioxide due to anthropogenic emissions is predicted to lead to significant changes in climate. About half of the current emissions are being absorbed by the ocean and by land ecosystems, but this absorption is sensitive to climate as well as to atmospheric carbon dioxide concentrations, creating a feedback loop. General circulation models have generally excluded the feedback between climate and the biosphere, using static vegetation distributions and CO2 concentrations from simple carbon-cycle models that do not include climate change. Here we present results from a fully coupled, three-dimensional carbon–climate model, indicating that carbon-cycle feedbacks could significantly accelerate climate change over the twenty-first century. We find that under a 'business as usual' scenario, the terrestrial biosphere acts as an overall carbon sink until about 2050, but turns into a source thereafter. By 2100, the ocean uptake rate of 5 Gt C yr-1 is balanced by the terrestrial carbon source, and atmospheric CO2 concentrations are 250 p.p.m.v. higher in our fully coupled simulation than in uncoupled carbon models, resulting in a global-mean warming of 5.5 K, as compared to 4 K without the carbon-cycle feedback.

/pdf/acceleration-of-global-warming-due-to-carbon-cycle-feedbacks-3788793i7v.pdf

Acceleration of global warming due to carbon-cycle feedbacks in a coupled climate model

Effects of retention harvests on structure of old-growth Pinus strobus L. stands in Ontario

Corticolous bryophytes, that is, mosses and liverworts that inhabit tree trunks, represent an important compo - nent of plant diversity in temperate ecosystems, but little is known of their ecology in managed forests In this study, we quantified community composition and habitat differentiation of corticolous bryophytes in Douglas-fir ( Pseudotsuga menziesii (Mirb) Franco) plantations subjected to experimental thinning and fertilization treatments Twenty-four bryophyte species were recorded in a sample of 480, 225 cm 2 quadrats on 60 tree trunks All moss species and obligately epiphytic liverworts (those with a primary habitat preference for tree trunks) showed highest cover values on south and west exposures In contrast, facultatively epiphytic liverworts occurred only at the tree base, and mainly on north and west exposures Pairwise correlations among species cover values were nearly always positive, and cover of the most abundant species, Isothecium myosuroides, was also positively correlated with local species richness of other bryophyte taxa These patterns suggest that competitive interactions among bryophyte species are not strong in this community There was little evidence for fertilization or thinning effects on total bryophyte cover or species richness However, analyses of community composition and species-specific responses indicated significant negative effects of thinning on some bryophyte species Observed patterns of habitat differentiation, interspecific associations, and treat- ment responses suggest that stand hydrology and microclimate are of primary importance in determining the distribu- tion and abundance of corticolous bryophytes in managed forests

https://faculty.washington.edu/chalpern/Thomas_et_al._2001.pdf

Corticolous bryophytes in managed Douglas-fir forests: habitat differentiation and responses to thinning and fertilization

Wood anatomical traits are important correlates of life-history strategies among tree species, yet little is known about wood chemical traits. Additionally, size-dependent changes in wood chemical traits have been rarely examined,althoughthesechangesmayrepresent animportantaspectoftreeontogeny.Owingtoselectionforpatho- gen resistance and biomechanical stability, we predicted that saplings would show higher lignin (L) and wood carbon (Cconv), and lower holocellulose (H) concentrations, compared with conspecific large trees. To test these expectations, we quantified H, L and Cconv in co-occurring Panamanian tree species at the large tree vs. sapling size classes. We also examined inter- and intraspecific patterns using multivariate and phylogenetic analyses. In 15 of 16 species, sapling L concentration was higher than that in conspecific large trees, and in all 16 species, sapling H was lower than that in conspecific large trees. In 16 of 24 species, Cconv was higher in saplings than conspecific large trees. All large-tree traits were unrelated to sapling values and were unrelated to four life-history variables. Wood chemical traits did not show a phylogenetic signal in saplings, instead showing similar values across distantly related taxa; in large trees, only H showed a significant phylogenetic signal. Size-dependent changes in wood chemistry show consistent and pre- dictable patterns, suggesting that ontogenetic changes in wood chemical traits are an important aspect of tree func- tional biology. Our results are consistent with the hypothesis that at early ontogenetic stages, trees are selected for greater L to defend against cellulose-decaying pathogens, or possibly to confer biomechanical stability.

/pdf/size-dependent-changes-in-wood-chemical-traits-a-comparison-1rh1248z0l.pdf

Size-dependent changes in wood chemical traits: a comparison of neotropical saplings and large trees

Assessing the potential of native tree species for carbon sequestration forestry in Northeast China

1 Although leaf morphology and chemistry show profound changes as trees age, the consequences of such changes to herbivory have received little attention, particularly late in the ontogeny of canopy trees

2 Using a mobile aerial lift for canopy access, patterns of leaf damage were evaluated in canopy-dominant mature sugar maple (Acer saccharum Marsh) trees ranging from ∼20 to 70 cm in diameter, corresponding to an age range of ∼40–180 years

3 Herbivore damage patterns varied in relation to both vertical canopy position (among upper-, mid-, and lower-canopy positions) and with tree size Damage types attributable to herbivores active on leaf surfaces, including leaf skeletonizers and leaf cutters (both principally Lepidoptera), and leaf stippling inducers (Hemiptera) showed decreases with tree size, and with increasing height in the canopy In contrast, leaf damage from the most abundant gall-forming arthropod in the system, the eriophyid mite Vasates aceriscrumena, increased markedly with tree size

4 The results indicate that herbivory patterns vary with both canopy stratum and with tree size in sugar maple, and that the relative strength of vertical stratification and tree ontogeny effects are similar in magnitude The predominant patterns are of a decrease in herbivory with increasing height in the canopy and with tree size, but certain galling arthropods exhibit the reverse trends

Sean C. Thomas

Papers

Effects of retention harvests on structure of old-growth Pinus strobus L. stands in Ontario

Corticolous bryophytes in managed Douglas-fir forests: habitat differentiation and responses to thinning and fertilization

Size-dependent changes in wood chemical traits: a comparison of neotropical saplings and large trees

Assessing the potential of native tree species for carbon sequestration forestry in Northeast China

Herbivory patterns in mature sugar maple: variation with vertical canopy strata and tree ontogeny