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

Global food demand is increasing rapidly, as are the environmental impacts of agricultural expansion. Here, we project global demand for crop production in 2050 and evaluate the environmental impacts of alternative ways that this demand might be met. We find that per capita demand for crops, when measured as caloric or protein content of all crops combined, has been a similarly increasing function of per capita real income since 1960. This relationship forecasts a 100–110% increase in global crop demand from 2005 to 2050. Quantitative assessments show that the environmental impacts of meeting this demand depend on how global agriculture expands. If current trends of greater agricultural intensification in richer nations and greater land clearing (extensification) in poorer nations were to continue, ∼1 billion ha of land would be cleared globally by 2050, with CO2-C equivalent greenhouse gas emissions reaching ∼3 Gt y−1 and N use ∼250 Mt y−1 by then. In contrast, if 2050 crop demand was met by moderate intensification focused on existing croplands of underyielding nations, adaptation and transfer of high-yielding technologies to these croplands, and global technological improvements, our analyses forecast land clearing of only ∼0.2 billion ha, greenhouse gas emissions of ∼1 Gt y−1, and global N use of ∼225 Mt y−1. Efficient management practices could substantially lower nitrogen use. Attainment of high yields on existing croplands of underyielding nations is of great importance if global crop demand is to be met with minimal environmental impacts.

https://www.pnas.org/content/pnas/108/50/20260.full.pdf

Global food demand and the sustainable intensification of agriculture

Humans continue to transform the global nitrogen cycle at a record pace, reflecting an increased combustion of fossil fuels, growing demand for nitrogen in agriculture and industry, and pervasive inefficiencies in its use. Much anthropogenic nitrogen is lost to air, water, and land to cause a cascade of environmental and human health problems. Simultaneously, food production in some parts of the world is nitrogen-deficient, highlighting inequities in the distribution of nitrogen-containing fertilizers. Optimizing the need for a key human resource while minimizing its negative consequences requires an integrated interdisciplinary approach and the development of strategies to decrease nitrogen-containing waste.

/pdf/transformation-of-the-nitrogen-cycle-recent-trends-questions-3hakfwkgng.pdf

Transformation of the Nitrogen Cycle: Recent Trends, Questions, and Potential Solutions

This paper contrasts the natural and anthropogenic controls on the conversion of unreactive N2 to more reactive forms of nitrogen (Nr). A variety of data sets are used to construct global N budgets for 1860 and the early 1990s and to make projections for the global N budget in 2050. Regional N budgets for Asia, North America, and other major regions for the early 1990s, as well as the marine N budget, are presented to highlight the dominant fluxes of nitrogen in each region. Important findings are that human activities increasingly dominate the N budget at the global and at most regional scales, the terrestrial and open ocean N budgets are essentially dis- connected, and the fixed forms of N are accumulating in most environmental reservoirs. The largest uncertainties in our understanding of the N budget at most scales are the rates of natural biological nitrogen fixation, the amount of Nr storage in most environmental reservoirs, and the production rates of N2 by denitrification.

/pdf/nitrogen-cycles-past-present-and-future-1zdbw0976r.pdf

Nitrogen cycles: past, present, and future

When a person looks at an object while exploring it with their hand, vision and touch both provide information for estimating the properties of the object. Vision frequently dominates the integrated visual-haptic percept, for example when judging size, shape or position, but in some circumstances the percept is clearly affected by haptics. Here we propose that a general principle, which minimizes variance in the final estimate, determines the degree to which vision or haptics dominates. This principle is realized by using maximum-likelihood estimation to combine the inputs. To investigate cue combination quantitatively, we first measured the variances associated with visual and haptic estimation of height. We then used these measurements to construct a maximum-likelihood integrator. This model behaved very similarly to humans in a visual-haptic task. Thus, the nervous system seems to combine visual and haptic information in a fashion that is similar to a maximum-likelihood integrator. Visual dominance occurs when the variance associated with visual estimation is lower than that associated with haptic estimation.

Humans integrate visual and haptic information in a statistically optimal fashion.

A new approach to estimate emissions of nitrous oxide from agriculture and its implications to the global N2O budget.

Information from field studies investigating the responses of roots to increasing atmospheric CO2 is limited and somewhat inconsistent, due partly to the difficulty in studying root systems in situ. In this report, we present standing root biomass of species and root length and diameter after five years of CO2 enrichment (720 lmol mol )1 ) in large (16 m 2 ground area) open-top chambers placed over a native shortgrass steppe in Colorado, USA. Total root biomass in 100 cm long20 cm wide75 cm depth soil monoliths and root biomass of the three dominant grass species of the site were not significantly affected by elevated CO2. Root biomass of Stipa comata in the 0–20 cm soil depth was nearly 100% greater in elevated vs. ambient CO2 chambers, but this was not statistically significant (P=0.14). However, there was a significant 37% increase in fine root length under elevated CO2 in the 0–10 cm soil depth layer. Other reports from this study suggest that the increase in fine roots is primarily from improved seedling recruitment of S. comata under elevated CO2. Few treatment differences in root length or diameter were detected in lower 10 cm depth increments, to 80 cm. These results reflect the root status integrated over two wet, two dry and one normal precipitation years and approximately one complete cycle of root turn-over on the shortgrass steppe. We conclude that increasing atmospheric CO2 will have only small effects on standing root biomass and root length and diameter of most shortgrasss steppe species. However, the potential increased competitive ability of Stipa comata, a low forage quality species, could alter the ecosystem from the current dominant, high forage quality species, Bouteloua gracilis. B. gracilis is very well adapted to the frequent droughts of the shortgrass steppe. Increased competitive ability of less desirable plant species under increasing atmospheric CO2 will have large implications for long-term sustainability of grassland ecosystems. Abbreviations: OTC – open top chamber

/pdf/root-biomass-of-individual-species-and-root-size-32kthpil84.pdf

Root Biomass of Individual Species, and Root Size Characteristics After Five Years of CO2 Enrichment on Native Shortgrass Steppe

Nitrification inhibitors are effective in decreasing direct nitrous oxide (N2O) emission from agricultural soils but may stimulate ammonia (NH3) volatilization. Part of the NH3 deposited to land is converted to N2O and emitted to the atmosphere, termed indirect N2O emission. While vegetable production systems entail a considerable risk of NH3 and N2O loss from high nitrogen (N) input to the soil, the simultaneous effects of nitrification inhibitors on these N loss pathways have rarely been examined. We conducted paddock-scale (ca. four hectares) measurements using micrometeorological techniques to simultaneously quantify the effects of a nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate) on NH3 and N2O emissions from two intensive vegetable farms. We found that DMPP decreased direct N2O emission by 37–38% (2.2–7.3 kg N ha−1) across the farms during the most intensive period of N input (18 days), but could increase NH3 volatilization by 3–39% (1.6–4.8 kg N ha−1). The results highlight the importance of considering multiple N loss pathways when developing a strategy for mitigating agricultural greenhouse gas emissions.

Direct and indirect greenhouse gas emissions from two intensive vegetable farms applied with a nitrification inhibitor

The effect of elevated carbon dioxide (CO2) concentration on symbiotic nitrogen fixation in soybean under open-air conditions has not been reported. Two soybean cultivars (Glycine max (L.) Merr. cv. Zhonghuang 13 and cv. Zhonghuang 35) were grown to maturity under ambient (415 ± 16 μmol mol−1) and elevated (550 ± 17 μmol mol−1) [CO2] at the free-air carbon dioxide enrichment experimental facility in northern China. Elevated [CO2] increased above- and below-ground biomass by 16–18% and 11–20%, respectively, but had no significant effect on the tissue C/N ratio at maturity. Elevated [CO2] increased the percentage of N derived from the atmosphere (%Ndfa, estimated by natural abundance) from 59% to 79% for Zhonghuang 13, and the amount of N fixed from 166 to 275 kg N ha−1, but had no significant effect on either parameter for Zhonghuang 35. These results suggest that variation in N2 fixation ability in response to elevated [CO2] should be used as key trait for selecting cultivars for future climate with respect to meeting the higher N demand driven by a carbon-rich atmosphere.

/pdf/effect-of-elevated-carbon-dioxide-on-growth-and-nitrogen-2la629gvm6.pdf

Effect of elevated carbon dioxide on growth and nitrogen fixation of two soybean cultivars in northern China

Gross rates of N mineralization, assimilation, nitrification, and NO
 in3
 sup-
 reduction were determined in soil from a wet riparian fen by 1-day incubations of soil cores and slurries with 15N-labelled substrates. N mineralization transformed 0.1% of the total organic N pool daily in the soil cores, of which 25% was oxidized through autotrophic nitrification and 53%–70% was incorporated into microorganisms. N mineralization and nitrification were markedly inhibited below 5 cm in soil depth. At least 80% of the NO
 in3
 sup-
 reduction in aerated cores occurred through dissimilatory processes. Dissimilatory reduction to NH
 in4
 sup+
 (DNRA) occurred only below 5 cm in depth. The results show that NH
 in4
 sup+
 oxidation was limited by available substrate and was itself a strong regulator of NO
 in3
 sup-
 -reducing activity. NO
 in3
 sup-
 reduction was significantly increased when the soil was suspended under anaerobiosis; adding glucose to the soil slurries increased NO
 in3
 sup-
 reduction by 2.4–3.7 times. Between 3% and 9% (net) of the added NO
 in3
 sup-
 was reduced through DNRA in the soil slurries. The highest percentage was observed in soil samples from deeper layers that were pre-incubated anaerobically.

Arvin R. Mosier

Papers

A new approach to estimate emissions of nitrous oxide from agriculture and its implications to the global N2O budget.

Root Biomass of Individual Species, and Root Size Characteristics After Five Years of CO2 Enrichment on Native Shortgrass Steppe

Direct and indirect greenhouse gas emissions from two intensive vegetable farms applied with a nitrification inhibitor

Effect of elevated carbon dioxide on growth and nitrogen fixation of two soybean cultivars in northern China

Nitrogen turnover rates in a riparian fen determined by 15N dilution