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31.
I. Opatovsky M. Elbaz I. Dori L. Avraham S. Mordechai-Lebiush A. Dombrovsky L. Tsror 《Plant pathology》2019,68(4):790-795
One of the economically important diseases of lettuce is lettuce big-vein disease (LBVD), which leads to severe yield losses. LBVD is associated with a complex of two viruses, Lettuce big-vein associated virus (LBVaV) and Mirafiori lettuce big-vein virus (MLBVV). These viruses are transmitted by motile zoospores of Olpidium spp. fungi, which persist in the soil for decades through resting spores. In greenhouse and field experiments, this study tested whether changing plant and soil temperatures together with fungicide application would have a significant effect on controlling LBVD in lettuce. Soil fumigation with metam sodium was not effective at controlling the disease, as opposed to treatment with chloropicrin and methyl bromide. Moreover, the fungicides carbendazim and fluazinam were effective in reducing the incidence of Olpidium virulentus. Nevertheless, control of the fungal vector did not seem to be sufficient to control the disease due to the transition ability of the virus under low vector abundance. Crop covers, which affect the favourable environmental conditions for the viruses by lowering soil temperature and raising air temperature, reduced the disease symptoms. Combining fungicides with crop cover had a synergistic effect on reducing disease symptoms, thus providing a sustainable solution for LBVD. 相似文献
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34.
Martin Pfeiffer;Georg Küstner;Erdenetsetseg Erdenesukh;Wolf von Tümpling;Jürgen Hofmann 《国际水土保持研究(英文)》2021,9(4):605-619
Headwater streams play a major role for provision of ecosystem services, e.g. drinking water. We investigated a high-altitude headwater catchment of the Kharaa River (including 41 1st-order rivers) to understand the impact of land cover (especially forest cover), environment and human usage on runoff, chemical water quality and macroinvertebrate fauna in a river basin under discontinuous permafrost conditions in an arid, sparsely populated region of Mongolia. To verify our hypotheses that different landuses and environmental impacts in permafrost headwaters influence water quality, we investigated 105 sampling sites, 37 of them at intermittent stream sections without water flow. Discharge was positively impacted by land cover types steppe, grassland and forest and negatively by shrubland, forest burnt by wild fires (indicating a reduction of permafrost) and slope. Water quality was affected by altitude, longitude and latitude, shrub growth and water temperature. Shannon diversity of macroinvertebrates was driven by water temperature, iron content of the water, flow velocity, and subbasin size (adjusted R2 = 0.54). Sample plots clustered in three groups that differed in water chemistry, macroinvertebrate diversity, species composition and bio-indicators. Our study confirms that steppes and grasslands have a higher contribution to runoff than forests, forest cover has a positive impact on water quality, and diversity of macroinvertebrates is higher in sites with less nutrients and pollutants. The excellent ecological status of the upper reaches of the Kharaa is severely threatened by forest fires and human-induced climate change and urgently needs to be conserved. 相似文献
35.
Landuse/cover in Nairobi City is changing rapidly because of the increased interactions of human activities with the environment as population increases. We used multi‐temporal Landsat images (1976, 1988 and 2000) together with physical and socio‐economic data in a post‐classification analysis with GIS to map landuse/cover distribution and to analyse factors influencing the landuse/cover changes for Nairobi City. An unsupervised classification approach, which uses a minimum spectral distance to assign pixels to clusters, was used with the overall accuracy ranging from 87 per cent to 90 per cent. Landuse/cover statistics revealed that substantial landuse/cover changes have taken place and that the built‐up areas have expanded by about 47 km2 over the study period (1976–2000). Forests have decreased substantially while agricultural lands have been on the increase. Rapid economic developments together with the increasing population were noted to be the major factors influencing rapid landuse/cover changes. Urban expansion has replaced agricultural farmlands and other natural vegetation, thereby affecting habitat quality and leading to serious environmental degradation. The random, unplanned growths of environmentally degraded squatter settlements were noted to be emerging in the rural fringes. Successful planning of Nairobi's development will require reliable information about landuse/cover changes and factors influencing such changes. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
36.
Peter Sørensen Betina N. Pedersen Ingrid K. Thomsen Jørgen Eriksen Bent T. Christensen 《植物养料与土壤学杂志》2023,186(4):441-450
Background
A high use-efficiency of fertilizer N remains essential to sustain high crop productivity with low environmental impact. However, little is known on the long-term lability of mineral fertilizer N.Aims
To quantify crop uptake and leaching of 15N-labelled mineral fertilizer that has been retained in an agricultural soil for 25–30 years in crops with variable growing season.Methods
A field plot received 15N-labelled mineral fertilizers over a period of 5 years and was then kept under arable cropping for 12 years. After relocation to 16 lysimeters, the topsoil grew set-aside grassland for the next 13 years. Then crop uptakes and leaching losses of 15N remaining in soil was tested over a 2-year period by either converting set-aside grass to production grassland, or by replacing it with spring barley (+/− autumn cover crop) or vegetation-free fallow. All treatments received unlabelled mineral N fertilizers.Results
Crop uptake and leaching of 15N were generally highest in the first test year after termination of the set-aside. The leaching of residual 15N in soil declined in the order: vegetation-free soil (4.7%), spring barley (1.9%), spring barley + cover crop (0.7%) and production grassland (0.2%). Corresponding losses for the second leaching period were 2.7%, 0.9%, 0.4% and 0.06%. There was a fixed relationship between leaching losses of 15N and total N.Conclusions
After residing in soil for 25–30 years, the lability of labelled mineral N fertilizer residues appeared slightly higher than the lability of bulk soil N. Autumn vegetation was crucial for reducing leaching losses. 相似文献37.
Paula Estelí Romero-Ovalle;María Victoria Campanella;Miguel Pascual;Martín García-Asorey;Cristian Pacheco;Cristian Barrionuevo;Alejandro Jorge Bisigato; 《Land Degradation u0026amp; Development》2024,35(3):1098-1109
During the last century shrub encroachment has occurred in many arid and semiarid areas of the world. Patagonia is a large xeric territory located in the southern tip of South America, which has been grazed by sheep for more than a century. In many areas overgrazing led to vegetation change (shrub encroachment), which in turn reduced sheep carrying capacity and caused ranch abandonment. However, these changes in physiognomy did not occur everywhere, and even some authors did not find evidence that shrub encroachment is currently occurring. Our objectives were to determine if encroachment really happened in NE Patagonia and, in the case of confirming shrub encroachment, to evaluate if the increase in shrub density was spatially homogeneous. We used object-based image analysis to evaluate shrub density and cover in aerial photographs taken in 1970 and 2018. In both dates, shrub density showed a clear contrast between two kinds of areas showing higher and lower density than was expected by chance. Shrub density and cover more than doubled between 1970 and 2018. This increase was concentrated in those areas with moderate or high densities of shrubs in 1970. Our results confirm the occurrence of shrub encroachment in NE Patagonia and demonstrate that it is currently concentrated near previously invaded areas. These findings have implications when defining protocols for monitoring shrub encroachment since monitors should focus on both areas that already have shrubs and areas that lack them. 相似文献
38.
Water use of spring wheat to raise water productivity 总被引：1，自引：0，他引：1
In semi-arid environments with a shortage of water resources and a risk of overexplotation of water supplies, spring wheat (Triticum aestivum L.) is a crop that can reduce water use and increase water productivity, because it takes advantage of spring rainfall and is harvested before the evaporative demands of summer. We carried out an experiment in 2003 at “Las Tiesas” farm, located between Barrax and Albacete (Central Spain), to improve accuracy in the estimation of wheat evapotranspiration (ETc) by using a weighing lysimeter. The measured seasonal ETc averages (5.63 mm day−1) measured in the lysimeter was 417 mm compared to the calculated ETc values (5.31 mm day−1) calculated with the standard FAO methodology of 393 mm. The evapotranspiration crop coefficient (Kc) derived from lysimetric measurements was Kc-mid: 1.20 and Kc-end: 0.15. The daily lysimeter Kc values were fit to the evolution linearly related to the green cover fraction (fc), which follows the crop development pattern. Seasonal soil evaporation was estimated as 135 mm and the basal crop coefficient approach was calculated in this study, Kcb which separates crop transpiration from soil evaporation (evaporation coefficient, Ke) was calculated and related to the green cover fraction (fc) and the Normalized Difference Vegetation Index (NDVI) obtained by field radiometry in case of wheat. The results obtained by this research will permit the reduction of water use and improvement of water productivity for wheat, which is of vital importance in areas of limited water resources. 相似文献
39.
Although land use change is the main driver of biodiversity decline in the South American temperate grasslands, its impacts on β-diversity have not yet been evaluated. We investigated relationships between β-diversity, landscape features, and geographical variables by surveying vegetation from 163 plots distributed in eight different land use types in Uruguay. We created land use maps using Landsat images and calculated landscape metrics, determining β-diversity across all plots and exploring variation of β-diversity among different land use types. We ran distance decay models to explore relationships between β-diversity and geographical location, climate, and landscape metrics. Plant species communities were characterized by a high turnover and low nestedness of species, indicating high dissimilarity across Uruguay. Native forest showed higher β-diversity than grassland, timber plantation, and crops. β-diversity increased with geographical distance and environmental dissimilarity. At landscape scale, turnover decreased negatively and nestedness increased to contagion, number of patches, and area-weighted mean. Nestedness increased with timber plantation and species turnover with crop area. Higher Landscape Shape Index of grassland and crops decreased species turnover. An increase of grassland and crop patches in the surrounding landscape was directly related to a higher species turnover. The high β-diversity across Uruguay resulting from land use change, moderated by landscape configurations, suggests that numerous protected areas for different habitats are urgently required. A more inclusive vision on biodiversity conservation is necessary, extending the predominant focus from native forests to grasslands, and convincing a broad range of stakeholders, especially landowners and managers, about biodiversity-friendly land-use approaches. 相似文献
40.
余田 《农业图书情报学刊》2012,24(5):155-159
研究发现,一些期刊一号多刊违反了一号一刊的规定,未对新增期刊申请新刊号,为逃避新闻出版署的检查,把频次标识为ⅹ月上旬、ⅹ月上半、A、下半月刊等形式,而不按实际发行情况标识旬刊、半月、月刊等形式,以及以月代期。一些期刊出版不遵守封面标识的有关规定,刊名不突出,或作夸大宣传,误导读者,外文刊未标识中文刊名。刊期标识也未遵循有关规定,较多期刊以月代期或不标识刊期;较多的期刊对月份的标识执行不力,未标识月的高达29.6%;对卷号的标识仅19.4%;部分期刊以总刊期代替刊期、卷号、年份、月份、频次。频次的标识,按发行实际正确标识的仅14.8%。标识的数字标准还有待统一,有标中文的和外文,而不是阿拉伯数字。调查的结果表明,期刊封面标识出版的有关规定执行并不乐观,还需要共同努力,提高期刊的综合出版质量。 相似文献