Five decades of northern land carbon uptake revealed by the interhemispheric CO2 gradient.

The global land and ocean carbon sinks have increased proportionally with increasing carbon dioxide emissions during the past decades1. It is thought that Northern Hemisphere lands make a dominant contribution to the global land carbon sink2-7; however, the long-term trend of the northern land sink remains uncertain. Here, using measurements of the interhemispheric gradient of atmospheric carbon dioxide from 1958 to 2016, we show that the northern land sink remained stable between the 1960s and the late 1980s, then increased by 0.5 ± 0.4 petagrams of carbon per year during the 1990s and by 0.6 ± 0.5 petagrams of carbon per year during the 2000s. The increase of the northern land sink in the 1990s accounts for 65% of the increase in the global land carbon flux during that period. The subsequent increase in the 2000s is larger than the increase in the global land carbon flux, suggesting a coincident decrease of carbon uptake in the Southern Hemisphere. Comparison of our findings with the simulations of an ensemble of terrestrial carbon models5,8 over the same period suggests that the decadal change in the northern land sink between the 1960s and the 1990s can be explained by a combination of increasing concentrations of atmospheric carbon dioxide, climate variability and changes in land cover. However, the increase during the 2000s is underestimated by all models, which suggests the need for improved consideration of changes in drivers such as nitrogen deposition, diffuse light and land-use change. Overall, our findings underscore the importance of Northern Hemispheric land as a carbon sink.

Europe-wide reduction in primary productivity caused by the heat and drought in 2003.

Future climate warming is expected to enhance plant growth in temperate ecosystems and to increase carbon sequestration. But although severe regional heatwaves may become more frequent in a changing climate, their impact on terrestrial carbon cycling is unclear. Here we report measurements of ecosystem carbon dioxide fluxes, remotely sensed radiation absorbed by plants, and country-level crop yields taken during the European heatwave in 2003. We use a terrestrial biosphere simulation model to assess continental-scale changes in primary productivity during 2003, and their consequences for the net carbon balance. We estimate a 30 per cent reduction in gross primary productivity over Europe, which resulted in a strong anomalous net source of carbon dioxide (0.5 Pg C yr(-1)) to the atmosphere and reversed the effect of four years of net ecosystem carbon sequestration. Our results suggest that productivity reduction in eastern and western Europe can be explained by rainfall deficit and extreme summer heat, respectively. We also find that ecosystem respiration decreased together with gross primary productivity, rather than accelerating with the temperature rise. Model results, corroborated by historical records of crop yields, suggest that such a reduction in Europe's primary productivity is unprecedented during the last century. An increase in future drought events could turn temperate ecosystems into carbon sources, contributing to positive carbon-climate feedbacks already anticipated in the tropics and at high latitudes.

Atmospheric deposition, CO2, and change in the land carbon sink.

Concentrations of atmospheric carbon dioxide (CO2) have continued to increase whereas atmospheric deposition of sulphur and nitrogen has declined in Europe and the USA during recent decades. Using time series of flux observations from 23 forests distributed throughout Europe and the USA, and generalised mixed models, we found that forest-level net ecosystem production and gross primary production have increased by 1% annually from 1995 to 2011. Statistical models indicated that increasing atmospheric CO2 was the most important factor driving the increasing strength of carbon sinks in these forests. We also found that the reduction of sulphur deposition in Europe and the USA lead to higher recovery in ecosystem respiration than in gross primary production, thus limiting the increase of carbon sequestration. By contrast, trends in climate and nitrogen deposition did not significantly contribute to changing carbon fluxes during the studied period. Our findings support the hypothesis of a general CO2-fertilization effect on vegetation growth and suggest that, so far unknown, sulphur deposition plays a significant role in the carbon balance of forests in industrialized regions. Our results show the need to include the effects of changing atmospheric composition, beyond CO2, to assess future dynamics of carbon-climate feedbacks not currently considered in earth system/climate modelling.

High resolution EELS of Cu-V oxides: application to batteries materials.

Although widely used, the most promising Li-based technologies still need to seek new materials concepts to satisfy the increasing demands for energy storage worldwide. We report a layered electrode material, Cu(2.33)V4O11, for which the valency of copper, vanadium and thus indirectly the oxygen stoichiometry need to be investigated during the electrochemical cycle. High-resolution electron energy loss spectroscopy (HREELS) allows us to perform these measurements at the nanometer scale.

Top-down assessment of the Asian carbon budget since the mid 1990s.

Increasing atmospheric carbon dioxide (CO2) is the principal driver of anthropogenic climate change. Asia is an important region for the global carbon budget, with 4 of the world's 10 largest national emitters of CO2. Using an ensemble of seven atmospheric inverse systems, we estimated land biosphere fluxes (natural, land-use change and fires) based on atmospheric observations of CO2 concentration. The Asian land biosphere was a net sink of -0.46 (-0.70-0.24) PgC per year (median and range) for 1996-2012 and was mostly located in East Asia, while in South and Southeast Asia the land biosphere was close to carbon neutral. In East Asia, the annual CO2 sink increased between 1996-2001 and 2008-2012 by 0.56 (0.30-0.81) PgC, accounting for ∼35% of the increase in the global land biosphere sink. Uncertainty in the fossil fuel emissions contributes significantly (32%) to the uncertainty in land biosphere sink change.

Comparative methods of quantifying fecal neutral sterols in rats and humans after intravenous [14C]-, [3H] or [2H]cholesterol labeling.

Several methods used to estimate the fecal elimination of neutral sterols and of cholesterol having a plasmatic origin (called 'excreted cholesterol') were compared in rats and humans according to the tracer intravenously administered: 14-14C], [1,2-3H]- or octadeuterated cholesterol. In both species, octadeuterated cholesterol had no isotopic effect and the chance occurrence of epicoprostanol in fecal sterols induced an error in the calculation of the fecal excretion of cholesterol. In humans, the use of [1,2-3H]cholesterol appeared to be inaccurate in measuring the fecal flows of cholesterol, because of a loss of 3H radioactivity during the bacterial transformation of cholesterol in the digestive tract. Consequently, the reference method needed to calculate the proportion of excreted cholesterol in fecal cholesterol consisted in dividing the isotopic concentration measured in purified fecal cholesterol by that measured in the appropriate plasma cholesterol sample.

Effects of the thyroid state on cholesterol metabolism in the rat.

An isotopic equilibrium method which permits the in vivo measurements of cholesterol turnover processes was applied to different groups of rats: (1) radiothyroidectomized, (2) low-iodine fed, and (3) L-thyroxin fed. Plasma cholesterol concentrations were enhanced after thyroidectomy and reduced by large dose of L-thyroxin. A low-iodine diet decreased plasma thyroxin level but did not affect plasma cholesterol. Thyroid levels in plasma modified the coefficient of intestinal absorption of cholesterol. After thyroidectomy or under conditions of reduced thyroxin formation this absorption coefficient was enhanced. The absorption coefficient of cholesterol was decreased in rats receiving 31 or 61.5 mug/day of L-thyroxin but was not changed in rats fed 110 mug/day L-thyroxin. The proportion of de novo biosynthetisized cholesterol eliminated into the feces (external secretion) was reduced while thyroxin levels were low. The fecal excretion of cholesterol and the in vitro exchange of cholesterol between erythrocytes and plasma were increased by L-thyroxin ingestion. The rate of cholesterol biosynthesis was decreased after thyroidectomy and enhanced by L-thyroxin feeding. In fact, changes in thyroid state modified indirectly the biosynthesis of cholesterol by its effects on metabolism and on the coefficient of intestinal absorption of cholesterol.

Cholesterol turnover in human plasma lipoproteins: studies with stable and radioactive isotopes.

The kinetics of cholesterol labeling was studied in the plasma lipoproteins of three subjects who had received an oral dose of octadeuterated cholesterol and an intravenous administration of 3H-cholesterol and 14C-mevalonate or 13C-acetate. After each labeled cholesterol pulse into the plasma (absorption, exchange, or synthesis), the isotopic concentrations of free and esterified cholesterol became identical after 120 h. Before this time, very low-density lipoprotein free cholesterol appeared more easily exchangeable than high-density and low-density lipoprotein free cholesterol, high-density lipoproteins were shown to be a source for very low-density lipoprotein cholesterol esters and the role of very low-density lipoproteins associated with chylomicrons was demonstrated in the initial transport of dietary cholesterol. The rates of the various processes involved in cholesterol turnover were calculated. The total cholesterol inflow into the plasma by absorption and synthesis, determined by long-term kinetic data (18 or 28 wk) was consistent with the result obtained by sterol balance for the total cholesterol outflow from the plasma (fecal excretion and conversion into bile acids).

In vivo study of cholesterol turnover in tissues of adult sows.

The in vivo study of free and esterified cholesterol turnover was carried out in 15 tissues of adult Large White sows maintained at a constant weight for 10-12 weeks. They received a single intravenous injection either of [1-14C] acetate, or of an autologous red cell suspension or of plasma, previously labelled in vitro (for red cells) or in vivo (for plasma) with tritiated cholesterol. The tissues can be separated into four groups according to their relative rate of free cholesterol exchange between plasma and tissues. The liver and the lungs have a very fast exchange rate whereas the brain and the spinal cord have a very slow one. The whole lipoprotein particle transfer--an exclusive model for the esterified cholesterol transport from plasma to tissues--has been found in all sow tissues. When [1-14C] acetate is used as a substrate for cholesterol synthesis, lungs, adrenal glands and heart do not seem--or at an extremely low rate--to convert acetate into cholesterol whereas an intense cholesterol synthesis takes place in the small intestine. Its contribution to cholesterol synthesis in sows--taking into account the cholesterol transfer processes--reaches 70 per cent.

Cholesterol turnover in swine plasma lipoproteins.

The kinetics of free and esterified cholesterol labeling were studied in the plasma lipoproteins of three groups of six adult Large White sows, after either an intravenous injection of autologous red cells previously labeled with [3H]-cholesterol, an intravenous injection of [14C]-acetate, or a [14C]-cholesterol labeled meal. The specific radioactivities became equal in plasma and red cell cholesterol about 96 hours after each pulse of radioactive cholesterol. This finding indicates that red cell cholesterol is completely exchangeable in vivo, with a turnover time of 8.5 hours. The VLDL were shown to play a preferential role in the transport in the plasma of newly synthetized cholesterol. This role is shared with chylomicrons in the transport of absorbed dietary cholesterol, which appears in the plasma mainly as esterified cholesterol. Cholesteryl esters of VLDL are not the main source for those of LDL, which could be labeled by intraplasmatic exchanges or transfers of esterified cholesterol.

In vivo study of free and esterified cholesterol turnover in various tissues of the rat.

Rats were infused for 3.5 to 10 hrs with either red cells or plasma previously labelled in vivo by [3H]-cholesterol. Cholesterol specific radioactivities were measured in plasma, HDL, LDL and VLDL, and various tissues. Red cell infusions led to a higher labelling of free than of esterified cholesterol in the plasma of infused rats. The opposite situation was observed following plasma infusion. Comparison of free and esterified cholesterol specific radioactivities in each tissue showed that esterified cholesterol was transferred from plasma to all the tissues, except the adrenals. Study of the ratios of cholesterol specific radioactivities from one experimental group to the other in each tissue, made it possible to demonstrate clearly the occurence of hydrolysis within all the studied tissues except 5 of them where its existence remains uncertain (lung, heart, kidney, tendon, muscle) and of esterification in 3 tissues (adrenal, liver lung). In addition, ratios of cholesterol radioactivities (free/ester) were found to be identical in plasma and in 4 tissues, where neither hydrolysis nor esterification were detected (heart, muscle, kidney, tendon). This finding is an argument in favor of a simultaneous transport of free and esterified cholesterol from plasma into these 4 tissues and suggests that the entire lipoprotein particles can penetrate these tissues, with no specificity of one special class. In adrenal, unlike all other tissues: 1) the turnover of esterified cholesterol was achieved mostly by hydrolysis and esterification in situ; 2) a preferential lipoprotein class (LDL) was responsible for the transport of free cholesterol from the plasma.

Effect of portacaval or mesentericocaval anastomosis on cholesterol metabolism in rats.

Portacaval anastomosis (PCA) lowered by 50% the cholesterol concentration in the plasma of rats. The free and esterified cholesterol contents in the lipoproteins were decreased with the very low density lipoproteins most affected (-85%). Cholesterol concentration as total content in the liver was reduced. The major change in the cholesterol metabolism, as studied with an isotopic equilibrium method, was the decrease in the intestinal absorption coefficient of dietary cholesterol (56.0 +/- 2.7% instead of 73.3 +/- 1.9% in controls). The rate of cholesterol transformation into bile acids was decreased (10.5 +/- 0.3 vs 14.5 +/- 0.5 mg/day/rat in controls). The rate of internal secretion of cholesterol was slightly reduced while the rate of fecal external secretion was increased, suggesting that the synthesis of cholesterol by extra-digestive tissues (including liver) was reduced after PCA. The effects of PCA on cholesterol metabolism were similar to those described for glucagon administration. Since this shunt results in hyperglucagonemia, it is suggested that this hormonal perturbation was the main factor involved in the modifications of cholesterol metabolism after PCA. Moreover, mesentericocaval anastomosis, which shunts only the intestinal blood and allows the pancreatic hormones a normal transport through the liver, did not significantly modify cholesterol metabolism. Only cholesterolemia (-28%) and the absorption coefficient of dietary cholesterol (66.0 +/- 2.3%) were slightly reduced.

Diet and sterol biohydrogenation in the rat: occurrence of epicoprostanol.

The fecal sterols from rats fed several types of semipurified or commercial diets were analyzed by a combination of thin layer and gas liquid chromatography. In rats fed semipurified diets with lard, sucrose, and casein, increasing proportions of lard (0, 8, 20, 65%) enhanced the fecal coprostanol/coprostanol + cholesterol ratio (from 0.50 to 0.85). This ratio was reduced by replacing lard with triolein or a mixture of calcium oleate and linoleate (1:1) and did not change when trierucin was substituted. No coprostanol formation was observed in rats fed a diet with tripalmitin or tristearin. The addition of sodium hyodeoxycholate (0.5%) or cholestyramine (2%) to the basal diet was without effect on the coprostanol/coprostanol + cholesterol ratio in the feces. The addition of sodium taurocholate (0.2, 0.75, and 4%) strongly reduced coprostanol formation, while a chronic bile duct ligation led to an enhancement. Cholesterol feeding (0.05, 0.2, and 0.5% in the diet) slightly increased (from 51 to 66%) coprostanol formation. Trace amounts of epicoprostanol were generally found in the feces. However, in some cases a very high proportion (up to 60%) of this sterol was observed. Possible relationships between the presence of epicoprostanol and the nature of the diet are discussed.

Fluctuations in blood cholesterol level: a rational analysis.

Laws governing rat and human blood cholesterol levels have been previously described. These laws reveal that cholesterol in the plasma constitutes an open non-linear system. In this hypothesis, the present paper attempts to explain the variations of cholesterolemia. As in every dynamic system, fluctuations can be observed after changes either in the orders of the system (inputs), or in the values of the parameters. The response of the system (cholesterolemia fluctuations) is analyzed in these various circumstances.