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101.
Matthias Saurer Renato Spahni David C. Frank Fortunat Joos Markus Leuenberger Neil J. Loader Danny McCarroll Mary Gagen Ben Poulter Rolf T.W. Siegwolf Laia Andreu‐Hayles Tatjana Boettger Isabel Dorado Liñán Ian J. Fairchild Michael Friedrich Emilia Gutierrez Marika Haupt Emmi Hilasvuori Ingo Heinrich Gerd Helle Håkan Grudd Risto Jalkanen Tom Levanič Hans W. Linderholm Iain Robertson Eloni Sonninen Kerstin Treydte John S. Waterhouse Ewan J. Woodley Peter M. Wynn Giles H.F. Young 《Global Change Biology》2014,20(12):3700-3712
The increasing carbon dioxide (CO2) concentration in the atmosphere in combination with climatic changes throughout the last century are likely to have had a profound effect on the physiology of trees: altering the carbon and water fluxes passing through the stomatal pores. However, the magnitude and spatial patterns of such changes in natural forests remain highly uncertain. Here, stable carbon isotope ratios from a network of 35 tree‐ring sites located across Europe are investigated to determine the intrinsic water‐use efficiency (iWUE), the ratio of photosynthesis to stomatal conductance from 1901 to 2000. The results were compared with simulations of a dynamic vegetation model (LPX‐Bern 1.0) that integrates numerous ecosystem and land–atmosphere exchange processes in a theoretical framework. The spatial pattern of tree‐ring derived iWUE of the investigated coniferous and deciduous species and the model results agreed significantly with a clear south‐to‐north gradient, as well as a general increase in iWUE over the 20th century. The magnitude of the iWUE increase was not spatially uniform, with the strongest increase observed and modelled for temperate forests in Central Europe, a region where summer soil‐water availability decreased over the last century. We were able to demonstrate that the combined effects of increasing CO2 and climate change leading to soil drying have resulted in an accelerated increase in iWUE. These findings will help to reduce uncertainties in the land surface schemes of global climate models, where vegetation–climate feedbacks are currently still poorly constrained by observational data. 相似文献
102.
The influence of local spring temperature variance on temperature sensitivity of spring phenology 总被引:2,自引:0,他引:2
Tao Wang Catherine Ottlé Shushi Peng Ivan A. Janssens Xin Lin Benjamin Poulter Chao Yue Philippe Ciais 《Global Change Biology》2014,20(5):1473-1480
The impact of climate warming on the advancement of plant spring phenology has been heavily investigated over the last decade and there exists great variability among plants in their phenological sensitivity to temperature. However, few studies have explicitly linked phenological sensitivity to local climate variance. Here, we set out to test the hypothesis that the strength of phenological sensitivity declines with increased local spring temperature variance, by synthesizing results across ground observations. We assemble ground‐based long‐term (20–50 years) spring phenology database (PEP725 database) and the corresponding climate dataset. We find a prevalent decline in the strength of phenological sensitivity with increasing local spring temperature variance at the species level from ground observations. It suggests that plants might be less likely to track climatic warming at locations with larger local spring temperature variance. This might be related to the possibility that the frost risk could be higher in a larger local spring temperature variance and plants adapt to avoid this risk by relying more on other cues (e.g., high chill requirements, photoperiod) for spring phenology, thus suppressing phenological responses to spring warming. This study illuminates that local spring temperature variance is an understudied source in the study of phenological sensitivity and highlight the necessity of incorporating this factor to improve the predictability of plant responses to anthropogenic climate change in future studies. 相似文献
103.
Modeling the Sensitivity of the Seasonal Cycle of GPP to Dynamic LAI and Soil Depths in Tropical Rainforests 总被引:1,自引:0,他引:1
The seasonality of pan-tropical wet forests has been highlighted by recent remote sensing and eddy flux measurements that
have recorded both increased and sustained dry-season gross primary productivity (GPP). These observations suggest that wet
tropical forests are primarily light limited and that the mechanisms for resilience to drought and projected climate change
must be considered in ecosystem model development. Here we investigate two proposed mechanisms for drought resilience of tropical
forests, deep soil water access and the seasonality of phenology, using the LPJmL Dynamic Global Vegetation Model. We parameterize
a new seasonal phenology module for tropical evergreen trees using remotely sensed leaf area index (LAI) and incoming solar
radiation data from the Terra Earth Observing System. Simulations are evaluated along a gradient of dry-season length (DSL)
in South America against MODIS GPP estimates. We show that deep soil water access is critical for maintaining dry-season GPP,
whereas implementing a seasonal LAI did not enhance simulated dry-season GPP. The Farquhar-Collatz photosynthesis scheme used
in LPJmL optimizes leaf nitrogen allocation according to light conditions, causing maximum photosynthetic capacity in the
dry season. High LAI, characteristic of tropical forests, also dampens the seasonal amplitude of the fraction of photosynthetically
active radiation (FPAR). Given the relatively high uncertainty in tropical phenology observations and their corresponding
proximate drivers, we recommend that ecosystem model development focus on belowground processes. An improved representation
of soil depths and rooting distributions is necessary for modeling the dynamics of dry-season tropical forest functioning
and may have important impacts for modeling tropical forest vulnerability to climate change.
Author Contributions BP conceived of the study, analyzed data, and wrote the paper. UH designed study and contributed new methods. WC designed
study and contributed to paper. 相似文献
104.
Annika A.M. Bokor Jan A.L. van Kan Russell T.M. Poulter 《Fungal genetics and biology : FG & B》2010,47(4):392-398
Strains of Botrytis cinerea are polymorphic for the presence of an intein in the Prp8 gene (intein +/?). The intein encodes a homing endonuclease (HEG). During meiosis in an intein +/? heterozygote, the homing endonuclease initiates intein ‘homing’ by inducing gene conversion. In such meioses, the homing endonuclease triggers gene conversion of the intein together with its flanking sequences into the empty allele. The efficiency of gene conversion of the intein was found to be 100%. The extent of flanking sequence affected by the gene conversion varied in different meioses. A survey of the inteins and flanking sequences of a group B. cinerea isolates indicates that there are two distinct variants of the intein both of which have active HEGs. The survey also suggests that the intein has been actively homing during the evolution of the species and that the PRP8 intein may have entered the species by horizontal transfer. 相似文献
105.
106.
Critical land change information enhances the understanding of carbon balance in the United States 总被引:1,自引:0,他引:1
Jinxun Liu Benjamin M. Sleeter Zhiliang Zhu Thomas R. Loveland Terry Sohl Stephen M. Howard Carl H. Key Todd Hawbaker Shuguang Liu Bradley Reed Mark A. Cochrane Linda S. Heath Hong Jiang David T. Price Jing M. Chen Decheng Zhou Norman B. Bliss Tamara Wilson Jason Sherba Qiuan Zhu Yiqi Luo Benjamin Poulter 《Global Change Biology》2020,26(7):3920-3929
Large‐scale terrestrial carbon (C) estimating studies using methods such as atmospheric inversion, biogeochemical modeling, and field inventories have produced different results. The goal of this study was to integrate fine‐scale processes including land use and land cover change into a large‐scale ecosystem framework. We analyzed the terrestrial C budget of the conterminous United States from 1971 to 2015 at 1‐km resolution using an enhanced dynamic global vegetation model and comprehensive land cover change data. Effects of atmospheric CO2 fertilization, nitrogen deposition, climate, wildland fire, harvest, and land use/land cover change (LUCC) were considered. We estimate annual C losses from cropland harvest, forest clearcut and thinning, fire, and LUCC were 436.8, 117.9, 10.5, and 10.4 TgC/year, respectively. C stored in ecosystems increased from 119,494 to 127,157 TgC between 1971 and 2015, indicating a mean annual net C sink of 170.3 TgC/year. Although ecosystem net primary production increased by approximately 12.3 TgC/year, most of it was offset by increased C loss from harvest and natural disturbance and increased ecosystem respiration related to forest aging. As a result, the strength of the overall ecosystem C sink did not increase over time. Our modeled results indicate the conterminous US C sink was about 30% smaller than previous modeling studies, but converged more closely with inventory data. 相似文献
107.
Jun Hata Hisatomi Arima Sophia Zoungas Greg Fulcher Carol Pollock Mark Adams John Watson Rohina Joshi Andre Pascal Kengne Toshiharu Ninomiya Craig Anderson Mark Woodward Anushka Patel Giuseppe Mancia Neil Poulter Stephen MacMahon John Chalmers Bruce Neal 《PloS one》2013,8(2)
Background
Endpoint adjudication committees (EPAC) are widely used in clinical trials. The aim of the present analysis is to assess the effects of the endpoint adjudication process on the main findings of the ADVANCE trial (Trial registration: ClinicalTrials.gov ). NCT00145925Methods and Findings
The ADVANCE trial was a multicentre, 2×2 factorial randomised controlled trial of blood pressure lowering and intensive blood glucose control in 11140 patients with type 2 diabetes. Primary outcomes were major macrovascular (nonfatal myocardial infarction, nonfatal stroke and cardiovascular death) and microvascular (new or worsening nephropathy and retinopathy) events. Suspected primary outcomes were initially reported by the investigators at the 215 sites with subsequent adjudication by the EPAC. The EPAC also adjudicated upon potential events identified directly by ongoing screening of all reported events. Over a median follow-up of 5 years, the site investigators reported one or more primary outcomes among 2443 participants. After adjudication these events were confirmed for 2077 (85%) with 48 further events added through the EPAC-led database screening process. The estimated relative risk reductions (95% confidence intervals) in the primary outcome for the blood pressure lowering comparison were 8% (−1 to 15%) based on the investigator-reported events and 9% (0 to 17%) based on the EPAC-based events (P for homogeneity = 0.70). The corresponding findings for the glucose comparison were 8% (1 to 15%) and 10% (2% to 18%) (P for homogeneity = 0.60). The effect estimates were also highly comparable when studied separately for macrovascular events and microvascular events for both comparisons (all P for homogeneity>0.6).Conclusions
The endpoint adjudication process had no discernible impact on the main findings in ADVANCE. These data highlight the need for careful consideration of the likely impact of an EPAC on the findings and conclusions of clinical trials prior to their establishment. 相似文献108.
James A. Poulter Musallam Al-Araimi Ivan Conte Maria M. van Genderen Eamonn Sheridan Ian M. Carr David A. Parry Mike Shires Sabrina Carrella John Bradbury Kamron Khan Phillis Lakeman Panagiotis I. Sergouniotis Andrew R. Webster Anthony T. Moore Bishwanath Pal Moin D. Mohamed Anandula Venkataramana Vedam Ramprasad Rohit Shetty Murugan Saktivel Govindasamy Kumaramanickavel Alex Tan David A. Mackey Alex W. Hewitt Sandro Banfi Manir Ali Chris F. Inglehearn Carmel Toomes 《American journal of human genetics》2013
109.
Joshua B. Fisher Munish Sikka Stephen Sitch Philippe Ciais Benjamin Poulter David Galbraith Jung-Eun Lee Chris Huntingford Nicolas Viovy Ning Zeng Anders Ahlstr?m Mark R. Lomas Peter E. Levy Christian Frankenberg Sassan Saatchi Yadvinder Malhi 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2013,368(1625)
The African humid tropical biome constitutes the second largest rainforest region, significantly impacts global carbon cycling and climate, and has undergone major changes in functioning owing to climate and land-use change over the past century. We assess changes and trends in CO2 fluxes from 1901 to 2010 using nine land surface models forced with common driving data, and depict the inter-model variability as the uncertainty in fluxes. The biome is estimated to be a natural (no disturbance) net carbon sink (−0.02 kg C m−2 yr−1 or −0.04 Pg C yr−1, p < 0.05) with increasing strength fourfold in the second half of the century. The models were in close agreement on net CO2 flux at the beginning of the century (σ1901 = 0.02 kg C m−2 yr−1), but diverged exponentially throughout the century (σ2010 = 0.03 kg C m−2 yr−1). The increasing uncertainty is due to differences in sensitivity to increasing atmospheric CO2, but not increasing water stress, despite a decrease in precipitation and increase in air temperature. However, the largest uncertainties were associated with the most extreme drought events of the century. These results highlight the need to constrain modelled CO2 fluxes with increasing atmospheric CO2 concentrations and extreme climatic events, as the uncertainties will only amplify in the next century. 相似文献
110.
Shilong Piao Stephen Sitch Philippe Ciais Pierre Friedlingstein Philippe Peylin Xuhui Wang Anders Ahlström Alessandro Anav Josep G. Canadell Nan Cong Chris Huntingford Martin Jung Sam Levis Peter E. Levy Junsheng Li Xin Lin Mark R Lomas Meng Lu Yiqi Luo Yuecun Ma Ranga B. Myneni Ben Poulter ZhenZhong Sun Tao Wang Nicolas Viovy Soenke Zaehle Ning Zeng 《Global Change Biology》2013,19(7):2117-2132
The purpose of this study was to evaluate 10 process‐based terrestrial biosphere models that were used for the IPCC fifth Assessment Report. The simulated gross primary productivity (GPP) is compared with flux‐tower‐based estimates by Jung et al. [Journal of Geophysical Research 116 (2011) G00J07] (JU11). The net primary productivity (NPP) apparent sensitivity to climate variability and atmospheric CO2 trends is diagnosed from each model output, using statistical functions. The temperature sensitivity is compared against ecosystem field warming experiments results. The CO2 sensitivity of NPP is compared to the results from four Free‐Air CO2 Enrichment (FACE) experiments. The simulated global net biome productivity (NBP) is compared with the residual land sink (RLS) of the global carbon budget from Friedlingstein et al. [Nature Geoscience 3 (2010) 811] (FR10). We found that models produce a higher GPP (133 ± 15 Pg C yr?1) than JU11 (118 ± 6 Pg C yr?1). In response to rising atmospheric CO2 concentration, modeled NPP increases on average by 16% (5–20%) per 100 ppm, a slightly larger apparent sensitivity of NPP to CO2 than that measured at the FACE experiment locations (13% per 100 ppm). Global NBP differs markedly among individual models, although the mean value of 2.0 ± 0.8 Pg C yr?1 is remarkably close to the mean value of RLS (2.1 ± 1.2 Pg C yr?1). The interannual variability in modeled NBP is significantly correlated with that of RLS for the period 1980–2009. Both model‐to‐model and interannual variation in model GPP is larger than that in model NBP due to the strong coupling causing a positive correlation between ecosystem respiration and GPP in the model. The average linear regression slope of global NBP vs. temperature across the 10 models is ?3.0 ± 1.5 Pg C yr?1 °C?1, within the uncertainty of what derived from RLS (?3.9 ± 1.1 Pg C yr?1 °C?1). However, 9 of 10 models overestimate the regression slope of NBP vs. precipitation, compared with the slope of the observed RLS vs. precipitation. With most models lacking processes that control GPP and NBP in addition to CO2 and climate, the agreement between modeled and observation‐based GPP and NBP can be fortuitous. Carbon–nitrogen interactions (only separable in one model) significantly influence the simulated response of carbon cycle to temperature and atmospheric CO2 concentration, suggesting that nutrients limitations should be included in the next generation of terrestrial biosphere models. 相似文献