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161.
Global change may have profound effects on soil nitrogen (N) cycling that can induce positive feedback to climate change through increased nitrous oxide (N2O) emissions mediated by nitrification and denitrification. We conducted a meta-analysis of the effects of elevated CO2 on nitrification and denitrification based on 879 observations from 58 publications and 46 independent elevated CO2 experiments in terrestrial ecosystems. We investigated the effects of elevated CO2 alone or combined with elevated temperature, increased precipitation, drought, and N addition. We assessed the response to elevated CO2 of gross and potential nitrification, potential denitrification, and abundances of related functional genes (archaeal amoA, bacterial amoA, nirK, nirS, and nosZ). Elevated CO2 increased potential nitrification (+28%) and the abundance of bacterial amoA functional gene (+62%) in cropland ecosystems. Elevated CO2 increased potential denitrification when combined with N addition and higher precipitation (+116%). Elevated CO2 also increased the abundance of nirK (+25%) and nirS (+27%) functional genes in terrestrial ecosystems and of nosZ (+32%) functional gene in cropland ecosystems. The increase in the abundance of nosZ under elevated CO2 was larger at elevated temperature and high N (+62%). Four out of 14 two-way interactions tested between elevated CO2 and elevated temperature, elevated CO2 and increased precipitation, and elevated CO2 and N addition were marginally significant and mostly synergistic. The effects of elevated CO2 on potential nitrification and abundances of bacterial amoA and nirS functional genes increased with mean annual temperature and mean annual precipitation. Our meta-analysis thus suggests that warming and increased precipitation in large areas of the world could reinforce positive responses of nitrification and denitrification to elevated CO2 and urges the need for more investigations in the tropical zone and on interactive effects among multiple global change factors, as we may largely underestimate the effects of global change on soil N2O emissions. 相似文献
162.
Yitong Yao Philippe Ciais Nicolas Viovy Emilie Joetzjer Jerome Chave 《Global Change Biology》2023,29(3):747-762
During the last two decades, inventory data show that droughts have reduced biomass carbon sink of the Amazon forest by causing mortality to exceed growth. However, process-based models have struggled to include drought-induced responses of growth and mortality and have not been evaluated against plot data. A process-based model, ORCHIDEE-CAN-NHA, including forest demography with tree cohorts, plant hydraulic architecture and drought-induced tree mortality, was applied over Amazonia rainforests forced by gridded climate fields and rising CO2 from 1901 to 2019. The model reproduced the decelerating signal of net carbon sink and drought sensitivity of aboveground biomass (AGB) growth and mortality observed at forest plots across selected Amazon intact forests for 2005 and 2010. We predicted a larger mortality rate and a more negative sensitivity of the net carbon sink during the 2015/16 El Niño compared with the former droughts. 2015/16 was indeed the most severe drought since 1901 regarding both AGB loss and area experiencing a severe carbon loss. We found that even if climate change did increase mortality, elevated CO2 contributed to balance the biomass mortality, since CO2-induced stomatal closure reduces transpiration, thus, offsets increased transpiration from CO2-induced higher foliage area. 相似文献
163.
Electrically induced calcium elevation,activation, and parthenogenetic development of bovine oocytes
Philippe Collas Rafael Fissore James M. Robl Eddie J. Sullivan Frank L. Barnes 《Molecular reproduction and development》1993,34(2):212-223
The influence of electrical stimulation on the level of intracellular Ca2+ in bovine oocytes, as well as activation and extent of parthenogenetic development, was investigated. Mature oocytes were electrically stimulated at 29 hr of maturation, and intracellular Ca2+ concentration was determined with the Ca2+ indicator fura-2 dextran (fura-2 D). The Ca2+ response of oocytes to a given electrical pulse was variable. Oocytes responded with either no Ca2+ rise from baseline (≈? 12 nM), a short-duration Ca2+ rise (from 12 nM to 300 nM) that returned to baseline within 2 min of the pulse, or a long-duration Ca2+ rise (from 12 nM to 1,000–2,000 nM) that never returned to baseline during the 8 min period over which the oocytes were monitored. In these oocytes, Ca2+ level returned to baseline when oocytes were removed from 0.30 M mannitol and placed in an ionic medium. Increasing field strength or pulse duration tended to increase the proportion of oocytes displaying a Ca2+ rise, and at 1.0 kVcm?1 for 40 μsec, all oocytes displayed a long-duration Ca2+ elevation. Direct transfer of oocytes from culture medium to mannitol also triggered a Ca2+ rise. Multiple stimulations, either electrical or by transferring to mannitol, produced multiple Ca2+ rises. This mannitol-induced Ca2+ rise could be inhibited by first washing the oocytes in medium containing equal parts of 0.30 M mannitol and phosphate buffered saline (PBS). The level of Ca2+ stimulation affected activation and development of oocytes. Insufficient, or, conversely, excessive Ca2+ stimulation impaired development. Optimum development was obtained with (1) three pulses of 0.2 kVcm?1 for 20 μsec, each pulse 22 min apart, after direct transfer of oocytes from culture medium to mannitol (22% blastocysts) or (2) three pulses of 1.0 kVcm?1 for 20 μsec after transfer of oocytes from culture medium to medium containing equal parts mannitol and PBS, then to mannitol (24% blastocysts). This procedure avoided induction of a Ca2+ rise prior to the pulse. The results indicate that the level of Ca2+ stimulation can be regulated by incubation conditions prior to the pulse and, to some extent, by field strength and pulse duration. The level of electrical stimulation influenced oocyte Ca2+ response, activation, and parthenogenetic development. © 1993 Wiley-Liss, Inc. 相似文献
164.
Jean-Fran ois Boe Philippe Goulas Jean-Louis Seris 《Biocatalysis and Biotransformation》1993,7(4):297-308
The effect of several organic acids on the oxidation of Mn(II) catalyzed by manganese peroxidase was studied. Reactivities of manganese peroxidase and chemically prepared Mn(III) organic acid complexes towards phenolic compounds were compared. If lactate appears to be the best complexant for manganese peroxidase activity, chemically prepared Mn(III)—lactate complex is a less effective oxidant towards phenolic compounds than other Mn(III)—complexes. Our results agree with the hypothesis that certain organic acids are involved in the catalytic cycle of manganese peroxidase. Malonate and lactate seem to be the most attractive complexants for practical applications of manganese peroxidase and were used in enzymatic treatment of hardwood kraft pulp. Bleaching of kraft pulp was studied and after alkaline extraction, a significant decrease of kappa number was measured. The bleaching was enhanced in lactate buffer. 相似文献
165.
Robin J. Boyd Martin Harvey David B. Roy Tony Barber Karen A. Haysom Craig R. Macadam Roger K. A. Morris Carolyn Palmer Stephen Palmer Chris D. Preston Pam Taylor Robert Ward Stuart G. Ball Oliver L. Pescott 《Diversity & distributions》2023,29(6):774-784
Aim
To develop a causal understanding of the drivers of Species distribution model (SDM) performance.Location
United Kingdom (UK).Methods
We measured the accuracy and variance of SDMs fitted for 518 species of invertebrate and plant in the UK. Our measure of variance reflects variation among replicate model fits, and taxon experts assessed model accuracy. Using directed acyclic graphs, we developed a causal model depicting plausible effects of explanatory variables (e.g. species' prevalence, sample size) on SDM accuracy and variance and quantified those effects using a multilevel piecewise path model.Results
According to our model, sample size and niche completeness (proportion of a species' niche covered by sampling) directly affect SDM accuracy and variance. Prevalence and range completeness have indirect effects mediated by sample size. Challenging conventional wisdom, we found that the effect of prevalence on SDM accuracy is positive. This reflects the facts that sample size has a positive effect on accuracy and larger sample sizes are possible for widespread species. It is possible, however, that the omission of an unobserved confounder biased this effect. Previous studies, which reported negative correlations between prevalence and SDM accuracy, conditioned on sample size.Main conclusions
Our model explicates the causal basis of previously reported correlations between SDM performance and species/data characteristics. It also suggests that niche completeness has similarly large effects on SDM accuracy and variance as sample size. Analysts should consider niche completeness, or proxies thereof, in addition to sample size when deciding whether modelling is worthwhile. 相似文献166.
Peter R. Bieck Karl-Heinz Antonin Gisbert Farger Erik B. Nilsson Eckhart K. Schmidt Philippe Dostert Margherita Strolin Benedetti Peter C. Waldmeier 《Neurochemical research》1993,18(11):1163-1167
CGP 28 014 is a specific inhibitor of catechol-O-methyltransferase (COMT) in vivo. In humans, the inhibition was assessed by measuring urinary excretion of isoquinolines and with the levodopa test. Following administration of CGP 28 014, urinary excretion of isoquinolines was significantly increased. In rats, CGP 28 014 reduced plasma and striatal concentrations of 3-O-methyldopa (30MD) in a dose-dependent manner. Acute and subchronic administration of CGP 28 014 alone or in combination with the peripherally acting decarboxylase inhibitor benserazide decreased plasma 30MD as an index of COMT inhibition by about 50%. There seems to be a close relationship between the time-course of plasma concentrations of CGP 28 014 and the extent of COMT inhibition assessed by the 30MD/DOPA ratio in plasma. 相似文献
167.
Zhi Jian Yu Changbae Jin Robin William Rockhold Beth Hoskins Ing Kang Ho 《Neurochemical research》1993,18(11):1203-1209
Wistar-Kyoto and spontaneously hypertensive rats received i.v. infusions of cocaine hydrochloride (60 mg/kg per day) for 3, 7, and 14 days, or saline for 7 days. Acute cocaine challenge (40 mg/kg, s.c.) was given to treated and control rats 24 hr after the termination of each infusion period. There were no strain differences in brain levels of cocaine during cocaine infusion, nor after cocaine challenges. There were no strain differences in resting levels of [3H]dopamine release. Release of [3H]dopamine decreased in nuclei accumbens of 7- and 14-day cocaine-infused animals. Release of [3H]dopamine was maximal in both brain regions 2 hr after acute cocaine challenge. After 14 days of cocaine infusion, cocaine challenge in both strains reduced [3H]dopamine release in the nucleus accumbens, but not in the striatum; the reduction being greater in Wistar-Kyoto rats. The behavioral tolerance which accompanies similar cocaine infusion regimens may be related to striatal tolerance to cocaine-induced dopamine release. 相似文献
168.
Paul L. Black Hamblin Phillips Henry R. Tribble Robin Pennington Mark schneider James E. Talmadge 《Cancer immunology, immunotherapy : CII》1993,37(5):299-306
The mechanism of therapeutic activity for recombinant murine interferon-(rMu IFN) in the treatment of metastatic disease was investigated by comparing effector cell augmentation with therapeutic activity in mice bearing experimental lung metastases (B16-BL6 melanoma). Effector cell functions in spleen, peripheral blood, and lung (the tumor-bearing organ) were tested after 1 week and 3 weeks of rMu IFN administration (i.v. three times per week). Natural killer (NK), lymphokine-activated killer (LAK), cytolytic T lymphocyte (CTL) activities against specific and nonspecific targets, and macrophage tumoristatic activity were measured. rMu IFN demonstrated immunomodulatory activity in most assays of immune function. The optimal therapeutic protocol of rMu IFN (2.5×106 U/kg, three times per week) prolonged survival and decreased the number of pulmonary metastatic foci. This therapeutic activity was correlated with specific CTL activity from pulmonary parenchymal mononuclear cells (PPMC), but not from spleen or blood. Macrophage tumoristatic activity in PPMC also correlated with therapeutic activity, but activity in alveolar macrophages did not. However, therapeutic activity did not correlate with NK or LAK activity at any site. These results demonstrate that the optimal therapeutic protocol is the same as the optimal immunomodulatory dose for pulmonary CTL and macrophage activities. Furthermore, while immunological monitoring may help to optimize treatment protocols, current monitoring procedures that use readily accessible sites, particularly peripheral blood, may not accurately predict the therapeutic efficacy of biological response modifiers in clinical trials.By acceptance of this article, the publisher or recipient acknowledges the right of the US. Government to retain a nonexclusive, royalty-free license in and to any copyright covering the articleThis research was sponsored by the DHHS, under contract N01-23910 with Program Resources Inc. The contents of this publication do not necessarily reflect the views or policies of the Department of Health and Human Services, nor does mention of trade names, commercial products, or organizations imply endorsement by the US Government 相似文献
169.
Valérie Michel Gérard Fonty Liliane Millet Frédérique Bonnemoy Philippe Gouet 《FEMS microbiology letters》1993,110(1):5-9
Abstract To better define the antigenic structure of the outer cell membranes of Legionellae, a panel of 6 monoclonal antibodies was raised against partially purified outer membranes of Legionella pneumophila serogroup 1, Corby strain. This study describes the purification and characterization of one of these monoclonal antibodies reacting with a 135-kDa protein, which was shown to be common to all 14 serogroups of Legionella pneumophila . It shows no cross-reactivity with 20 other Legionella species, or 9 other Gram-negative species tested by SDS-PAGE and Western blotting procedures. The epitope would appear to be predominantly surface exposed and, from preliminary detergent extraction studies, not peptidoglycan-associated. 相似文献
170.
Vincent Calcagno Patrice David Philippe Jarne François Massol 《Ecology letters》2023,26(Z1):S140-S151
How the complexity of food webs depends on environmental variables is a long-standing ecological question. It is unclear though how food-chain length should vary with adaptive evolution of the constitutive species. Here we model the evolution of species colonisation rates and its consequences on occupancies and food-chain length in metacommunities. When colonisation rates can evolve, longer food-chains can persist. Extinction, perturbation and habitat loss all affect evolutionarily stable colonisation rates, but the strength of the competition-colonisation trade-off has a major role: weaker trade-offs yield longer chains. Although such eco-evo dynamics partly alleviates the spatial constraint on food-chain length, it is no magic bullet: the highest, most vulnerable, trophic levels are also those that least benefit from evolution. We provide qualitative predictions regarding how trait evolution affects the response of communities to disturbance and habitat loss. This highlights the importance of eco-evolutionary dynamics at metacommunity level in determining food-chain length. 相似文献