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91.
Modelling climate response to historical land cover change 总被引:9,自引:0,他引:9
Victor Brovkin rey Ganopolski Martin Claussen Claudia Kubatzki Vladimir Petoukhov 《Global Ecology and Biogeography》1999,8(6):509-517
In order to estimate the effect of historical land cover change (deforestation) on climate, we perform a set of experiments with a climate system model of intermediate complexity – CLIMBER-2. We focus on the biophysical effect of the land cover change on climate and do not explicitly account for the biogeochemical effect. A dynamic scenario of deforestation during the last millennium is formulated based on the rates of land conversion to agriculture. The deforestation scenario causes a global cooling of 0.35 °C with a more notable cooling of the northern hemisphere (0.5 °C). The cooling is most pronounced in the northern middle and high latitudes, especially during the spring season. To compare the effect of deforestation on climate with other forcings, climate responses to the changing atmospheric CO2 concentration and solar irradiance are also analysed. When all three factors are taken into account, dynamics of northern hemisphere temperature during the last 300 years within the model are generally in agreement with the observed (reconstructed) temperature trend. We conclude that the impact of historical land cover changes on climate is comparable with the impact of the other climate forcings and that land cover forcing is important for reproducing historical climate change. 相似文献
92.
Changes in the 2H and 18O of atmospheric water vapour provide information for integrating aspects of gas exchange within forest canopies. In this study, we show that diurnal fluctuations in the oxygen isotope ratio (δ18O) as high as 4‰ were observed for water vapour (δ18Ovp) above and within an old‐growth coniferous forest in the Pacific Northwest region of the United States. Values of δ18Ovp decreased in the morning, reached a minimum at midday, and recovered to early‐morning values in the late afternoon, creating a nearly symmetrical diurnal pattern for two consecutive summer days. A mass balance budget was derived and assessed for the 18O of canopy water vapour over a 2‐d period by considering the 18O‐isoflux of canopy transpiration, soil evaporation and the air entering the canopy column. The budget was used to address two questions: (1) do δ18O values of canopy water vapour reflect the biospheric influence, or are such signals swamped by atmospheric mixing? and (2) what mechanisms drive temporal variations of δ18Ovp? Model calculations show that the entry of air into the canopy column resulted in an isotopically depleted 18O‐isoflux in the morning of day 1, causing values of δ18Ovp to decrease. An isotopically enriched 18O‐isoflux resulting from transpiration then offset this decreased δ18Ovp later during the day. Contributions of 18O‐isoflux from soil evaporation were relatively small on day 1 but were more significant on day 2, despite the small H216O fluxes. From measurements of leaf water volume and sapflux, we determined the turnover time of leaf water in the needles of Douglas‐fir trees as ≈ 11 h at midday. Such an extended turnover time suggests that transpiration may not have occurred at the commonly assumed isotopic steady state. We tested a non‐steady state model for predicting δ18O of leaf water. Our model calculations show that assuming isotopic steady state increased isoflux of transpiration. The impact of this increase on the modelled δ 18Ovp was clearly detectable, suggesting the importance of considering isotopic non‐steady state of transpiration in studies of forest 18O water balance. 相似文献
93.
Arvanitoyannis IS Bosinas KP Bouletis AD Gkagtzis DC Hadjichristodoulou C Papaloucas C 《Anaerobe》2011,17(6):300-302
The aim of the present work was to evaluate the effect of atmosphere modification on microbial (mesophiles, yeast and molds) qualities, color, pH, texture and water activity of the Greek bakery product “touloumpaki”. Samples were stored under MAP (60% CO2) either alone or with the addition of honey syrup for 16 days at room temperature (22–24 °C). Texture was better maintained under MAP and the addition of honey prevented the increase of shear force needed (1.498 and 3.20 for samples with and without honey). Honey inhibited the growth of yeasts on samples stored under MAP (1.6 and 2.02 log CFU/g for samples under MAP with and without honey respectively) while multivariant analysis showed that MAP and honey acted synergistically in confining yeasts. Presence of honey restrained the mesophilic growth until the end of storage period (5.21 and 4.29 log CFU/g for MAP and control samples respectively) while MAP did not have any beneficial effect. Water activity (aW < 0.754) was strongly associated with reduced mesophile growth. Lightness values showed a significant decrease during time with no significant changes among treatments in both internal layers and external surface of the product. 相似文献
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96.
腐食酪螨对低氧高二氧化碳气调的抗性 总被引:3,自引:0,他引:3
在10%CO_2,5%O_2(其余部分为N_2,下同);35%CO_2,11%CO_2;35%CO_2,21%O_2;75%CO_2,11%O_2,及75%CO_2,21%O_2,五种气调环境下对腐食酪螨Tyrophagus putrescentiae(Schrank)进行连续25~26代的抗气性诱导筛选。结果表明,抗性都有不同程度的增加,在75%CO_2,11%O_2下抗性系数最大为5.0,在10%CO_2,5%O_2下抗性系数最小为3.7,在其它气调环境下,抗性系数都在4以上。 相似文献
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98.
The field of prebiotic chemistry effectively began with a publicationin Science 50 years ago by Stanley L. Miller on the spark discharge synthesis of amino acids and other compounds using a mixture of reduced gases that were thought to represent the components of the atmosphere on the primitive Earth. On the anniversary of this landmark publication, weprovide here an accounting of the events leading to the publication of the paper. We also discuss the historical aspects that lead up to the landmark Miller experiment. 相似文献
99.
In the present study, the effect of type of stunning (electrical v. gas) and the gas mixtures in a modified atmosphere (MA) packing system (MA-A: 30% CO2 + 70% O2; MA-B: 30% CO2 + 69.3% N2 + 0.7% CO; MA-C: 40% CO2 + 60% N2) on light lamb meat quality, obtained by 20 males of Manchego Spanish breed, was evaluated at 7, 14 and 21 days post packing. For all ageing times, gas-stunned groups reached the highest pH (P < 0.001) and shear force (SF) values (P < 0.05), and at 21 days, water losses were highest; in contrast, meat colour coordinates were lower (P < 0.001). In general, MA-B showed the highest stability for colour coordinates whereas the lowest tenderness (high SF) was found on MA-A. In this study, the gas mixture with a low carbon monoxide level (MA-B) promoted a higher colour stability and good tenderness, in comparison to the other two blends. In contrast, the conventional packaging system (type A, high oxygen levels) had a reduced tenderness and major colour instability. 相似文献
100.