共查询到20条相似文献,搜索用时 7 毫秒
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农田生态系统是对人类生存发展具有重大影响的生态系统之一。农田生态系统生产力水平与影响作物生长发育的自然环境因子如光、气、热、水、肥、土等具有不可分割的联系。其中一些环境因子如光、气、热等在一定的区域内和较长的时间范围内并无显著变化差异, 相似文献
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《Journal of biological education》2012,46(2):138-141
Giving land an ecological value is a problem in many student projects. This paper suggests a method which is suitable for a range of abilities Any methods used by students for evaluating the ecological or conservation value of an area under study need to be relatively simple, as it is unlikely that they will have a specialist knowledge of ecology. The most frequently used criteria in site evaluation are difficult to apply at secondary education level, and a method has been developed which relies only on recognition of major habitat types and landscape features. The example used is a comparison of two possible sites for location of a sewage treatment works, and a ‘total ecological score’ is obtained for each site. This can then be used to calculate possible ‘units of ecological damage’ in the event of a development on the land. Damage can also be categorized as reversible or irreversible to allow for reinstatement and mitigation work. Students can then incorporate these estimates as part of a wider impact analysis and decision-making process and the methods can be applied to any development. 相似文献
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Robert C. Hunt 《Human ecology: an interdisciplinary journal》2000,28(2):251-277
Labor productivity is a major component of agricultural development. Boserup is the scholar most associated with the view that labor productivity declines with intensification of agriculture. This paper reviews the theoretical argument and empirical support for the decline thesis. An empirical test is conducted by means of a comparative study of traditional rice agriculture in Southeast Asia. The decline thesis is rejected. The implications for agricultural development are discussed. 相似文献
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W. J. Elliot 《CMAJ》1965,93(21):1134-1135
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Maozhen Han Melissa Dsouza Chunyu Zhou Hongjun Li Junqian Zhang Chaoyun Chen Qi Yao Chaofang Zhong Hao Zhou Jack A Gilbert Zhi Wang Kang Ning 《基因组蛋白质组与生物信息学报(英文版)》2019,17(1):76-90
Agricultural activities, including stock-farming, planting industry, and fish aquaculture,can affect the physicochemical and biological characters of freshwater lakes. However, the effects of pollution producing by agricultural activities on microbial ecosystem of lakes remain unclear.Hence, in this work, we selected Honghu Lake as a typical lake that is influenced by agriculture activities. We collected water and sediment samples from 18 sites, which span a wide range of areas from impacted and less-impacted areas. We performed a geospatial analysis on the composition of microbial communities associated with physicochemical properties and antibiotic pollution of samples. The co-occurrence networks of water and sediment were also built and analyzed. Our results showed that the microbial communities of impacted and less-impacted samples of water were largely driven by the concentrations of TN, TP, NO_3^--N, and NO_2^--N, while those of sediment were affected by the concentrations of Sed-OM and Sed-TN. Antibiotics have also played important roles in shaping these microbial communities: the concentrations of oxytetracycline and tetracycline clearly reflected the variance in taxonomic diversity and predicted functional diversity between impacted and less-impacted sites in water and sediment samples, respectively. Furthermore, for samples from both water and sediment, large differences of network topology structures between impacted and less-impacted were also observed. Our results provide compelling evidence that the microbial community can be used as a sentinel of eutrophication and antibiotics pollution risk associated with agricultural activity; and that proper monitoring of this environment is vital to maintain a sustainable environment in Honghu Lake. 相似文献
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Jacqueline Swartz 《CMAJ》1989,140(10):1206-1207
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Zehui Jiang 《Plant biosystems》2013,147(2):127-131
Abstract A pollen diagram from a small lake, Kutulahdenlampi, in northern Finland is interpreted in terms of the development of forest vegetation during the Holocene. The abundance of each of the forest taxa is considered independently by means of pollen accumulation rates (PARs), using as the reference material, long term average pollen deposition values monitored by a network of pollen traps. Particular attention is paid to the arrival of spruce and to the species in the original forests that this newcomer replaces. A model of pollen dispersal and deposition developed by Sugita is used to estimate the area around the lake that the pollen assemblage is most clearly reflecting. This relevant source area of pollen (RSAP), for the present day situations is c. 1,500 m. Pollen loadings calculated for a simulated landscape that mimics (i) that of the present day and (ii) for the situation at 8,000 BP (as deduced from the PARs) are compared with the pollen assemblages from the diagram at those points in time, and are seen to be compatible. The advantages of combining PAR and modelling to look at the spatial scale of vegetation reconstructions are discussed. 相似文献
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J?rg Müller Valentin H. Klaus Till Kleinebecker Daniel Prati Norbert H?lzel Markus Fischer 《PloS one》2012,7(12)
While bryophytes greatly contribute to plant diversity of semi-natural grasslands, little is known about the relationships between land-use intensity, productivity, and bryophyte diversity in these habitats. We recorded vascular plant and bryophyte vegetation in 85 agricultural used grasslands in two regions in northern and central Germany and gathered information on land-use intensity. To assess grassland productivity, we harvested aboveground vascular plant biomass and analyzed nutrient concentrations of N, P, K, Ca and Mg. Further we calculated mean Ellenberg indicator values of vascular plant vegetation. We tested for effects of land-use intensity and productivity on total bryophyte species richness and on the species richness of acrocarpous (small & erect) and pleurocarpous (creeping, including liverworts) growth forms separately. Bryophyte species were found in almost all studied grasslands, but species richness differed considerably between study regions in northern Germany (2.8 species per 16 m2) and central Germany (6.4 species per 16 m2) due environmental differences as well as land-use history. Increased fertilizer application, coinciding with high mowing frequency, reduced bryophyte species richness significantly. Accordingly, productivity estimates such as plant biomass and nitrogen concentration were strongly negatively related to bryophyte species richness, although productivity decreased only pleurocarpous species. Ellenberg indicator values for nutrients proved to be useful indicators of species richness and productivity. In conclusion, bryophyte composition was strongly dependent on productivity, with smaller bryophytes that were likely negatively affected by greater competition for light. Intensive land-use, however, can also indirectly decrease bryophyte species richness by promoting grassland productivity. Thus, increasing productivity is likely to cause a loss of bryophyte species and a decrease in species diversity. 相似文献
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Soil Carbon Accumulation During Temperate Forest Succession on Abandoned Low Productivity Agricultural Lands 总被引:2,自引:0,他引:2
Carbon sequestration in soils that have previously been depleted of organic matter due to agriculture is an important component of global strategies to mitigate rising atmospheric CO2 concentrations. Extensive areas of low productivity farmland have been abandoned from agriculture in eastern North America and elsewhere over the past century, and are naturally regenerating to temperate forests. We investigated the soil carbon sequestration potential of such lands by sampling adjacent mature forest and agricultural field sites, and replicated chronosequences of forest succession on Podzol, Brunisol, and Luvisol soil types that are considered ‘marginal’ for agriculture and have been abandoned extensively across southeastern Ontario, Canada. Total soil organic carbon and nitrogen stocks to 10 cm depth were approximately 32% and 18% lower, respectively, in agricultural fields compared to mature forests. Furthermore, carbon stocks across our 100-year chronosequences increased most within the 0–5 cm soil depth interval, tended to increase within the 5–10 cm interval, and were unaltered within the 10–20 cm interval. Soil type had little effect on the potential magnitude or rates of soil carbon sequestration (~10 g C m?2 y?1 in the top 10 cm), perhaps because all sites shared a common vegetation successional pattern. Finally, our investigations of the ‘labile’ free-light carbon and nitrogen fractions in the Brunisol soil type indicated no increases across the chronosequence, implying that soil carbon accumulation was primarily in more recalcitrant pools. Our results indicate that each of these low productivity soil types can be moderate carbon sinks for a century following agricultural abandonment, and strongly suggest that time since abandonment is more important than soil type in determining the potential magnitude of carbon sequestration within this climatic region. 相似文献