共查询到20条相似文献,搜索用时 15 毫秒
1.
Does a warmer climate with frequent mild water shortages protect grassland communities against a prolonged drought? 总被引:1,自引:0,他引:1
C. Zavalloni B. Gielen C. M. H. M. Lemmens H. J. De Boeck S. Blasi S. Van den Bergh I. Nijs R. Ceulemans 《Plant and Soil》2008,309(1-2):119-130
While irrigation of farm dairy effluent (FDE) to land is becoming popular in New Zealand, it can lead to increased emissions of the greenhouse gas nitrous oxide (N2O). This paper reports the results from trials on N2O emissions from irrigation of FDE to two dairy-grazed pastures on two poorly drained silt-loam soils located at Waikato and Manawatu, New Zealand. These pasture soils were periodically irrigated with FDE under contrasting soil moisture conditions with water-filled pore-space (WFPS) ranging between 26% and 94%. Nitrous oxide emissions were measured from the FDE irrigated and unirrigated sites using large numbers of static chambers (12–20). Irrigation of FDE generally increased N2O emissions compared to the control. N2O emissions varied with changes in climatic conditions and soil WFPS. Overall N2O emissions from effluent-derived N ranged between 0.01% and 4.93% depending on irrigation time and soil WFPS. Lower N2O emissions from FDE were attributable to very low soil WFPS conditions during the dry seasons. Higher N2O emissions were measured from application of FDE to a recently grazed pasture on wet soil. Our results suggest strategic application of FDE during dry summer and autumn seasons can reduce N2O emissions from application of FDE. Delaying effluent-irrigation after grazing events could further reduce N2O emissions by reducing the levels of surplus mineral-N. 相似文献
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3.
Renata Bączek-Kwinta Agnieszka Adamska Katarzyna Seidler-Łożykowska Krzysztof Tokarz 《Biologia》2010,65(5):837-842
The response of the wild type (WT) and a strain C6/2 of German chamomile to 7-d soil drought and subsequent 7-day rehydration was studied. Shoot and leaf growth, vegetative development, water and protein contents, ascorbate peroxidase activity and gas exchange were compared. At the stress stage, water content of WT plants was slightly influenced and the effect was ceased after rehydration. Also the decrease in gas exchange was temporary. New leaves were formed, although their area was diminished. On the contrary, leaves of C6/2 plants were more desiccated and the durable decrease in water content was accompanied by the impairment in gas exchange also at the recovery stage (20–40% loss when compared to the control). At both stages of the experiment the growth of the long shoots of this genotype was drastically decreased, as well as leaf formation. Ascorbate peroxidase activity was increased by drought in leaves of both genotypes, but the pattern of changes in WT plants reflected the enhancement of metabolism resulting from proper water content and gas exchange at the recovery stage. Different pattern of changes in the protein content during drought was also noticed: a slight increase in WT, while the decrease by ¼ in C6/2 leaves. The response of WT plants to desiccation and rewatering was found to be more elastic than that of C6/2. 相似文献
4.
What truly happened in the terrestrial ecosystems in response to the famous Messinian salinity crisis is still the matter of extensive discussions. Did mammals record any faunal and/or a climatic or environmental fluctuation is a question that still remains open. Our objective is to investigate mammalian faunas before, during and after the crisis within different terrestrial basins surrounding the Mediterranean Sea. We therefore apply here two methods, the cenogram method and a transfer function based on murine (rodents) species richness to better understand if our proxies can record any qualitative or quantitative climatic or environmental change. The results indicate that mammal faunas do not record any particular shift in climate or environment at the scale of the whole peri-Mediterranean area. The trend is different at the regional scale of terrestrial basins as temperatures increase (Calatayud-Daroca-Teruel Basin) or decrease (Languedoc-Roussillon region) punctually occurs just after the crisis; stable conditions in different areas (e.g. Greece) contradict these trends. Biases in the fossil record or in the methodologies could produce such discrepancies. 相似文献
5.
Manti L 《Radiation and environmental biophysics》2006,45(1):1-8
This review addresses the purported interplay between actual or simulated weightlessness and cellular response to ionizing radiation. Although weightlessness is known to alter several cellular functions and to affect signaling pathways implicated in cell proliferation, differentiation and death, its influence on cellular radiosensitivity has so far proven elusive. Renewed controversy as to whether reduced gravity enhances long-term radiation risk is fueled by recently published data that claim either overall enhancement of genomic damage or no increase of radiation-induced clastogenicity by modeled microgravity in irradiated human cells. In elucidating this crucial aspect of space radiation protection, ground-based experiments, such as those based on rotating-wall bioreactors, will increasingly be used and represent a more reproducible alternative to in-flight experiments. These low-shear vessels also make three-dimensional cellular co-cultures possible and thus allow to study the gravisensitivity of radioresponse in a context that better mimics cell-to-cell communication and hence in vivo cellular behavior. 相似文献
6.
Experiments were conducted to examine the effects of long-term fertilization and acute Zn toxicity on the size, nitrification activity and community structure of autotrophic ammonia-oxidizing populations of the β-subgroup of the class Proteobacteria in arable soils. Plots under different long-term fertilization regimes were sampled, and then different concentrations of ZnCl2 were spiked into soil samples for 8 weeks. It was found that long-term fertilization significantly increased nitrification rates and population size, and there was a positive correlation between them. A shift in the composition of AOB was also detected in samples fertilized with mineral N fertilizer (NPK) and organic matter (OM) as compared to unfertilized sample. EC50 values suggested that there was no significant difference in Zn toxicity to nitrification rates among the three fertilization treatments. Long-term fertilization did not improve the resilience of AOB activity to Zn toxicity. 相似文献
7.
Raimo Virkkala Risto K. Heikkinen Stefan Fronzek Heini Kujala Niko Leikola 《Biodiversity and Conservation》2013,22(2):459-482
Species ranges are expected to move polewards following the changing climate, which poses novel challenges to the protected area network, particularly at northern latitudes. Here we study how well protected areas are likely to sustain populations of birds of conservation concern under a changing climate in northern Europe, in Finland. We fitted bioclimatic envelope models generated for 100 bird species to climate scenario data for the years 2051–2080 and three alternative emission scenarios in a 10-km grid system to predict changes in the species probability of occurrence. We related the projected changes in the climatic suitability to the amount of protected preferred habitat for the study species in the 10-km grid cells, and based on the cover of four main CORINE Land Cover classes in each conservation area in Finland. The probability of occurrence of all species (except marshland birds) decreased according to all scenarios, the decline being greatest in southern and smallest in northern boreal zones. This decline was slightly greater in unprotected than in protected areas for species of forests, mires and mountain habitats. The climatically suitable areas for the species were predicted to shift northwards, but the potential gain of southern species of conservation concern appears not to compensate for the loss of northern species. Thus, a representative protected area network is needed in all boreal zones. Overall, our results show that species-specific habitat preferences and habitat availability should be taken into account when assessing the efficiency of a protected area network in a changing climate. 相似文献
8.
Does nitrogen nutrition restrict the CO2 response of fertile grassland lacking legumes? 总被引:7,自引:0,他引:7
S. Zanetti U. A. Hartwig C. van Kessel A. Lüscher T. Hebeisen M. Frehner B. U. Fischer G. R. Hendrey H. Blum J. Nösberger 《Oecologia》1997,112(1):17-25
The extent of the response of plant growth to atmospheric CO2 enrichment depends on the availability of resources other than CO2. An important growth-limiting resource under field conditions is nitrogen (N). N may, therefore, influence the CO2 response of plants. The effect of elevated CO2 (60 Pa) partial pressure (pCO2) on the N nutrition of field-grown Lolium perenne swards, cultivated alone or in association with Trifolium repens, was investigated using free air carbon dioxide enrichment (FACE) technology over 3 years. The established grassland ecosystems
were treated with two N fertilization levels and were defoliated at two frequencies. Under elevated pCO2, the above-ground plant material of the L. perenne monoculture showed a consistent and significant decline in N concentration which, in general, led to a lower total annual
N yield. Despite the decline in the critical N concentration (minimum N concentration required for non-N-limited biomass production)
under elevated pCO2, the index of N nutrition (ratio of actual N concentration and critical N concentration) was lower under elevated pCO2 than under ambient pCO2 in frequently defoliated L. perenne monocultures. Thus, we suggest that reduced N yield under elevated pCO2 was evoked indirectly by a reduction of plant-available N. For L. perenne grown in association with T. repens and exposed to elevated pCO2, there was an increase in the contribution of symbiotically fixed N to the total N yield of the grass. This can be explained
by an increased apparent transfer of N from the associated N2-fixing legume species to the non-fixing grass. The total annual N yield of the mixed grass/legume swards increased under
elevated pCO2. All the additional N yielded was due to symbiotically fixed N. Through the presence of an N2-fixing plant species more symbiotically fixed N was introduced into the system and consequently helped to overcome N limitation
under elevated pCO2.
Received: 11 November 1996 / Accepted: 20 May 1997 相似文献
9.
Does proximity to a mature forest contribute to the seed rain and recovery of an abandoned agriculture area in a semiarid climate? 总被引:1,自引:0,他引:1
J. T. Souza E. M. N. Ferraz U. P. Albuquerque E. L. Araújo 《Plant biology (Stuttgart, Germany)》2014,16(4):748-756
Proximity to forests contributes to the recolonisation of anthropogenic‐disturbed areas through seed input. We evaluated the role of proximity to a mature forest in the recolonisation of an agricultural area that has been abandoned for 18 years and is currently a young forest. Seed rain was monitored at fixed distances from the mature forest. The type of surface recolonisation (germination versus resprouting) and the reproductive season were measured in both forests. The majority of plants recolonising the young forest originated from seed germination. Proximity to the mature forest contributed to the seed rain in the young forest; however, 18 years has not provided sufficient time for the recolonisation of 80 species present in the mature forest. Some species shared between forests differed in their fruiting season and seed dispersal. The seed rain had a total species richness of 56, a total density of 2270 seeds·m?2·year?1 and predominance of self‐ and wind dispersal. A significant reduction in seed rain with increasing distance from the mature forest was observed. The young forest contained 35 species not observed in the mature forest, and the floristic similarity between the two forests was 0.5, indicating that the two forests are floristically distinct. 相似文献
10.
Grace JB Michael Anderson T Smith MD Seabloom E Andelman SJ Meche G Weiher E Allain LK Jutila H Sankaran M Knops J Ritchie M Willig MR 《Ecology letters》2007,10(8):680-689
Theoretical analyses and experimental studies of synthesized assemblages indicate that under particular circumstances species diversity can enhance community productivity through niche complementarity. It remains unclear whether this process has important effects in mature natural ecosystems where competitive feedbacks and complex environmental influences affect diversity–productivity relationships. In this study, we evaluated diversity–productivity relationships while statistically controlling for environmental influences in 12 natural grassland ecosystems. Because diversity–productivity relationships are conspicuously nonlinear, we developed a nonlinear structural equation modeling (SEM) methodology to separate the effects of diversity on productivity from the effects of productivity on diversity. Meta-analysis was used to summarize the SEM findings across studies. While competitive effects were readily detected, enhancement of production by diversity was not. These results suggest that the influence of small-scale diversity on productivity in mature natural systems is a weak force, both in absolute terms and relative to the effects of other controls on productivity. 相似文献
11.
The water potential at turgor loss point (Ψtlp) has been suggested as a key functional trait for determining plant drought tolerance, because of its close relationship with stomatal closure. Ψtlp may indicate drought tolerance as plants, which maintain gas exchange at lower midday water potentials as soil water availability declines also have lower Ψtlp. We evaluated 17 species from seasonally dry habitats, representing a range of life‐forms, under well‐watered and drought conditions, to determine how Ψtlp relates to stomatal sensitivity (pre‐dawn water potential at stomatal closure: Ψgs0) and drought strategy (degree of isohydry or anisohydry; ΔΨMD between well‐watered conditions and stomatal closure). Although Ψgs0 was related to Ψtlp, Ψgs0 was better related to drought strategy (ΔΨMD). Drought avoiders (isohydric) closed stomata at water potentials higher than their Ψtlp; whereas, drought tolerant (anisohydric) species maintained stomatal conductance at lower water potentials than their Ψtlp and were more dehydration tolerant. There was no significant relationship between Ψtlp and ΔΨMD. While Ψtlp has been related to biome water availability, we found that Ψtlp did not relate strongly to stomatal closure or drought strategy, for either drought avoiders or tolerators. We therefore suggest caution in using Ψtlp to predict vulnerability to drought. 相似文献
12.
Climate models predict an increasing frequency of extremely hot summer events in the northern hemisphere for the near future.
We hypothesised that microbial grazing by the metazoan macrofauna is an interaction that becomes unbalanced at high temperatures
due to the different development of the grazing rates of the metazoans and the growth rates of the microbial community with
increasing temperature. In order to test this hypothesis, we performed grazing experiments in which we measured the impact
of increasing temperatures on the development of the grazing rates of riverine mussels in relation to the growth rates of
a unicellular prey community (a natural heterotrophic flagellate community from a large river). In a first experimental series
using Corbicula fluminea as a grazer and under the addition of a carbon source (yeast extract), the increase of the prey’s growth rates was considerably
stronger than that of the predator’s grazing rates when temperatures were increased from 19 to over 25°C. This was also the
outcome when the mussels had been acclimatized to warm temperatures. Hereafter, specific experiments with natural river water
at temperatures of 25 and 30°C were performed. Again, a strong decrease of the mussels’ grazing rates in relation to the flagellate
growth rates with increasing temperature occurred for two mussel species (C. fluminea and Dreissena polymorpha). When performing the same experiment using a benthic microbial predator community (biofilms dominated by ciliates) instead
of the benthic mussels, an increase of the grazing rates relative to the growth rates with temperature could be observed.
Our data suggest that predator–prey interactions (between metazoans and microbes) that are balanced at moderate temperatures
could become unbalanced at high temperatures. This could have significant effects on the structure and function of microbial
communities in light of the predicted increasing frequency of summer heat waves.
Priority programme of the German Research Foundation—contribution 7. 相似文献
13.
Michael Danger Tanguy Daufresne Françoise Lucas Serge Pissard Gérard Lacroix 《Oikos》2008,117(11):1741-1751
Liebig's law of the minimum, which states that only one element limits the growth of organisms at any given time, is widely used in ecology. This principle is routinely applied to organisms, populations and communities, but can it really be applied indistinguishably across these different scales? Here we show, by prediction of a resource ratio conceptual model and with an experimental test carried out in microcosms with bacteria that, unlike single species, communities are likely to adjust their stoichiometry to that of their resources. This adjustment results from competitive exclusion and coexistence mechanisms, and is sensitive to the overall diversity of species in the community. It guaranties co‐limitation, i.e. simultaneous limitation by multiple resources, at the community scale and optimal use of resources and maximization of community biomass for wide ranges of resource ratios. These results question the applicability of the Liebig's law of the minimum at the community level, and the relevance of ecosystem models relying on this principle. 相似文献
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Summary Iljin's experiments withRhoeo discolor, cabbage and red beet which seemed to demonstrate increased drought resistance of plasmolysed tissue have been repeated, but his results could not be confirmed. The tissue plasmolysed in sucrose solutions, died either during stepwise plasmolysis and deplasmolysis or else later on, during exposure to unsaturated air within one or two days, even at the highest humidities. Iljin's error was apparently produced by a wrong interpretation of his tests of viability: the plasma of his dead cells did not disintegrate and retained anthocyanin by tonoplast plasmolysis.Plasmolysis proved harmful to all three objects investigated.In view of these results and earlier criticism of Iljin's analogous experiments on frost resistance by others, all experimental evidence produced in support of Iljin's mechanical theory of drought resistance should be reexamined. 相似文献
16.
Does the response of the intestinal epithelium to keratinocyte growth factor vary according to the method of administration? 总被引:3,自引:0,他引:3
BACKGROUND: Keratinocyte growth factor (KGF) is a potent mitogen and may be of value for the treatment of conditions such as short bowel syndrome and chemotherapy-induced mucositis. However the most efficacious route and method of administration is unclear. METHODS: Rats maintained by total parenteral nutrition (TPN) were given KGF (1 mg/kg/rat/day, i.v.) infused continuously or as a once-daily injection. The same dose was also given s.c. to chow-fed rats. Changes in gut growth were assessed by measurement of wet weight, proliferation (vincristine induced metaphase arrest) and crypt branching index. Changes in gut hormone profile were also determined to examine if any trophic effects were mediated via this mechanism. RESULTS: KGF caused a 70-100% increase in wet weight of the stomach, small and large intestine of TPN-fed rats (P < 0.01) with no significant differences seen between the two methods of administration. The increase in metaphase counts was greatest in the stomach (about seven-fold P < 0.01), but was less pronounced in the distal small intestine and colon (about 50% increase). The trophic effect of KGF was much less prominent in orally-fed rats. Crypt branching index was significantly reduced by KGF in the proximal small intestine of TPN, but not orally-fed rats. Plasma gastrin, PYY, total glucagon, enteroglucagon and GLP-1 all increased by two-three-fold (all P < 0.01) in response to KGF whereas insulin levels fell by about 25% in the TPN group. CONCLUSIONS: The mitogenic action of KGF occurred predominantly in the stomach and proximal small intestine. Its efficacy was less pronounced in orally-fed animals, suggesting KGF may be of greatest benefit in conditions associated with lowered intestinal proliferation. Clinical trials of KGF can probably use single daily i.v. injections without reduction in efficacy. 相似文献
17.
Differences among lake morphologies often explain variation in characteristics of lentic ecosystems. Although beaver ponds
also vary in morphology, previous studies have not examined the effects of such variation on downstream ecosystems. This study
evaluated downstream effects of multiple beaver ponds in the Colorado Rocky Mountains during one low and one high-flow year.
Beaver pond morphology was described as the natural log transformed ratio of beaver dam height (which determines hydraulic
head) to pond surface area and related to pond spillover phytoplankton and characteristics of the ecosystem downstream (nutrient
concentrations, limiting nutrients, periphyton, benthic organic matter (BOM), and benthic invertebrate consumers). Nitrate
concentration increased systematically downstream of beaver ponds, but only in the low flow year when groundwater influences
predominated. Effects of beaver ponds on soluble reactive phosphorus concentration depended on pond morphology, increasing
downstream of small ponds with high dams, but only during the low-flow year. In situ experiments showed that neither beaver
activity nor pond morphology predicted periphyton-limiting nutrients downstream. Both periphyton biomass and BOM decreased
downstream of small ponds with high dams but pond morphology did not predict abundance of invertebrate grazers or detritus-feeding
consumers. While suspension feeding invertebrates increased downstream from small ponds with high dams, variation in chlorophyll
a from water spilling over beaver dams did not follow a similar pattern. We conclude that the effects of beaver ponds on downstream
nutrients, resources and consumers are rarely systematic, but instead depend on variation in pond morphology and on annual
hydrologic variation. 相似文献
18.
Does engineering abscisic acid biosynthesis in Nicotiana plumbaginifolia modify stomatal response to drought? 总被引:5,自引:1,他引:4
C. Borel A. Frey A. Marion-Poll F. Tardieu & T. Simonneau 《Plant, cell & environment》2001,24(5):477-489
The consequences of manipulating abscisic acid (ABA) biosynthesis rates on stomatal response to drought were analysed in wild‐type, a full‐deficient mutant and four under‐producing transgenic lines of N. plumbaginifolia. The roles of ABA, xylem sap pH and leaf water potential were investigated under four experimental conditions: feeding detached leaves with varying ABA concentration; injecting exogenous ABA into well‐watered plants; and withholding irrigation on pot‐grown plants, either intact or grafted onto tobacco. Changes in ABA synthesis abilities among lines did not affect stomatal sensitivity to ABA concentration in the leaf xylem sap ([ABA]xyl), as evidenced with exogenous ABA supplies and natural increases of [ABA]xyl in grafted plants subjected to drought. The ABA‐deficient mutant, which is uncultivable under normal evaporative demand, was grafted onto tobacco stock and then presented the same stomatal response to [ABA]xyl as wild‐type and other lines. This reinforces the dominant role of ABA in controlling stomatal response to drought in N. plumbaginifolia whereas roles of leaf water potential and xylem sap pH were excluded under all studied conditions. However, when plants were submitted to soil drying onto their own roots, stomatal response to [ABA]xyl slightly differed among lines. It is suggested, consistently with all the results, that an additional root signal of soil drying modulates stomatal response to [ABA]xyl. 相似文献
19.
Ying Fan Shibin Ding Xiaolei Ye Anne Manyande Dongliang He Nana Zhao Huiqin Yang Xin Jin Jian Liu Chong Tian Shunqing Xu Chenjiang Ying 《Hormones and behavior》2013
Bisphenol A (BPA) is a ubiquitous environmental endocrine disrupting compound (EDC); public health concerns have been fueled by findings that maternal BPA exposure can change sex differences in the brain and in some behaviors. We investigated whether a physiologically relevant dose of BPA ingested by male rats before conception would affect spatial memory and hippocampal acetylcholinesterase (AchE) in their adult offspring. Twenty-two 60-day-old male rats (F0) received either a BPA diet (50 μg/kg/day) or vehicle alone for 10 weeks before being mated with non-exposed females. The paternal rats and their forty adult offspring's (F1) behaviors were then examined in the Morris Water Maze (MWM) and their AchE activities in the hippocampus were evaluated. BPA exposure led to spatial memory deficits along with decreased AchE activities in the hippocampus (p = 0.01) in adult F0 rats. This paternal exposure also induced impairment in spatial memory acquisition in both sexes while retention only in females in F1 rats, as well as abolished sex differences in the hippocampus AchE. Overall, these data provide new evidence that paternal BPA exposure, at a “safe” dose, may induce transgenerational alterations in spatial memory in a sex-specific manner. 相似文献
20.
Aurelien Mondon 《Ethnic and racial studies》2017,40(13):2151-2179
This article will examine the construction and functions of, as well as relationship between, the diverse and changing articulations of Islamophobia. The aim is to contribute to debates about the definition of Islamophobia, which have tended to be contextually specific, fixed and/or polarized between racism and religious prejudice, between extreme and mainstream, state and non-state versions or undifferentiated, and offer a more nuanced framework to: (a) delineate articulations of Islamophobia as opposed to precise types and categories; (b) highlight the porosity in the discourse between extreme articulations widely condemned in the mainstream, and normalized and insidious ones, which the former tend to render more acceptable in comparison; (c) map where these intersect in response to events, historical and political conditions and new ideological forces and imperatives and (d) compare these articulations of Islamophobia in two contexts, France and the US. 相似文献