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61.
《Journal of Sustainable Forestry》2013,32(3):83-93
Abstract Mineralization is the dominant process controlling soil-solution P in the Spodosols of the southeastern United States. Pine trees growing in these soils are typically colonized by ectomycorrhizal (EM) fungi that are known to produce phosphatases. Little, however, is known of the dynamics of EM short roots or phosphatase activity in tree plantations. To address this question, short root densities, EM morphotypes, and associated surface acid phosphomonoesterase in a 12-year-old Pinus elliottii plantation in northern Florida were evaluated. The density of total (living and dead) short roots changed little from February through June, with a mean of 7.6 cm3 soil. The majority of the short roots, however, were inactive or dead with only 14 to 38% appearing viable upon visual inspection. The majority of the viable short roots were mycorrhizal. The most abundant morphotypes were formed by Cenococcum and Thelephora but these had low phosphatase activity. In contrast, less frequently observed morphotypes had substantially higher rates of enzyme production and these may play an important role in sustainable P nutrition of plantation trees. 相似文献
62.
老子的自然哲学观中具有丰富的生态伦理意蕴,主要表现为老子自然哲学观中“道法自然”的生态智慧观,“天人合一”的生态和谐观和“万物自化”的生态社会观。研究它们对于保护生态环境和认识人与自然和谐的意义,对于全面落实科学发展观,都有重要的时代价值。 相似文献
63.
64.
气候变化对内蒙古农牧业生态环境的影响 总被引:2,自引:1,他引:2
分析了数十年来气候变暖对内蒙古农牧业生态环境的影响。发现气候变暖使内蒙古地区无霜期延长,积雪、冰雹、雷暴、大风、沙尘暴日数减少,降水量也出现由少转多的变化。事实表明,气候增暖使内蒙古总的生态环境出现向好转化,但是增暖所带来的负面影响是病虫害的增加,加上人为的作用,严重地破坏了内蒙古的生态平衡。 相似文献
65.
Recent research shows that land use history is an important determinant of current ecosystem function. In the United States,
characterization of land use change following European settlement requires reconstruction of the original property mosaic.
However, this task is difficult in unsystematically surveyed areas east of the Appalachian Mountains. The Gwynns Falls watershed
(Baltimore, MD) was originally surveyed in the 1600-1700s under a system of warrants and patents (commonly known as ‘metes
and bounds’). A method for the reconstruction and mapping of warrant and patent properties is presented and used to map the
original property mosaic in the Gwynns Falls watershed. Using the mapped mosaic, the persistence of properties and property
lines in the current Gwynns Falls landscape is considered. The results of this research indicate that as in agricultural areas,
the original property lines in the Gwynns Falls watershed are persistent. At the same time, the results suggest that the property
mosaic in heavily urbanized/suburbanized areas is generally ‘reset.’ Further, trends in surveying technique, parcel size,
and settlement patterns cause property line density and property shape complexity to increase in the less urbanized upper
watershed. The persistence of original patterns may be damping expression of heterogeneity gradients in this urban landscape.
This spatial pattern of complexity in the original mosaic is directly opposite of hypothesized patterns of landscape heterogeneity
arising from urbanization. The technique reported here and the resulting observations are important for landscape pattern
studies in areas settled under unsystematic survey systems, especially the heavily urbanized areas of the eastern United States.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
66.
Helge Green Nina Heiberg Kirsten Lejbølle Dan Funck Jensen 《European journal of plant pathology / European Foundation for Plant Pathology》2001,107(3):349-359
The activity of Trichoderma harzianum in the spermosphere and rhizosphere of different plant species was studied by use of a beta-glucuronidase (GUS) transformant (strain T3a). Hereby, direct observation of micro-habitats supporting metabolic activity of T. harzianum is reported. Germination of conidia and mycelial growth were not supported by exudates from healthy roots of various ages. Instead, growth and activity of T. harzianum depended on access to dead organic substrates such as seed coats, decaying roots, and wounds, including those caused by infecting pathogens. A correlation between the GUS activity of T. harzianum and the biomass of Pythium ultimum in infected roots was established. On the basis of our observations, we suggest that the biocontrol ability of T. harzianum involves competition with the pathogen for substrates including the seed coat, and wounded or infected root tissue. 相似文献
67.
68.
Improved understandings of the agricultural and range ecologies ofsemi-arid Africa require better information on the spatiotemporal distributionof domestic livestock across agropastoral landscapes. An empirical GIS-basedapproach was developed for estimating distributions of herded livestock acrossthree agropastoral territories (around 100 km2 each)over a two-year period. Algorithms developed from regression analyses of herdtracking data (with R2s 0.67) are used to transform a morecomprehensive but incomplete set of data generated from herders accounts oftheir herds grazing itineraries (400 herds following 6500 itineraries). Theresulting characterization registers 40 000 days of livestock activitiesacross694 land units (averaging 70 ha) over the study period. This studydemonstrates that rural producers knowledge of their daily extractionpracticescan be translated to fine-grained characterizations of extraction densitiesacross mixed landscapes. The spatiotemporal distribution of livestock that isrevealed by this approach diverges strongly from that predicted bycommonly-usedpoint-diffusion estimation procedures. Instead, the distribution reflects localpatterns of land use, topography, vegetation, settlements, and water points.Grazing and nongrazing times spent in land units are not spatially correlatedand the seasonality of grazing pressure is spatially variable. Therefore, theecological impacts of livestock grazing are spatially variable at fine scalesand there is a significant potential for livestock-mediated nutrient transfersacross agropastoral landscapes. The georeferenced data produced by thisapproachnot only will help evaluate the impact and sustainability of differentmanagement practices but also provides a strong empirical base for improvedspatial modeling of herded livestock.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
69.
洮儿河沿岸地区水利工程建设的生态水文影响初探 总被引:6,自引:0,他引:6
张艳红 《干旱区资源与环境》2006,20(4):133-137
水利工程建设在获得社会经济利用的同时也对生态水文问题造成明显的负面影响,在干旱半干旱地区此类问题尤为显著。本文分别探讨了洮儿河沿岸地区三类水利工程即水库、防洪堤和灌渠对于流域生态水文的影响,主要体现在:(1)减少水库下游河流径流量,加重下游水资源短缺问题;严重影响下游沼泽湿地水文,导致湿地退化(2)灌渠建设使地下水位抬升,加重土壤次生盐渍化问题;(3)防洪堤修建改变湿地水质,增大其矿化度和碱度。 相似文献
70.
Repeated sequences of digitised and geo-referenced historical aerial photography provide a powerful means of understanding
landscape change. We use this method to demonstrate a landscape wide expansion of closed forest (42% increase in total coverage)
in the Australian monsoon tropics over the past five decades. Retrospective habitat suitability models (HSI) of closed forest
derived using four landscape measures (drainage distance, slope angle, aspect and elevation) for imagery taken in 1947 correctly
forecast the subsequent spatial distribution of the expansion, with topographic fire protection primarily determining the
closed-forest distribution. The dynamics of the closed forest-savanna boundary were predicted accurately by generalised linear
models, with closed-forest expansion in fire-protected sites along forest edges and regression in the more fire-prone areas.
Two factors may plausibly explain the expansion of closed forests. First, eco-ethnographic records stress the skilful use
of fire by Aboriginal people in protecting isolated and locally resource-rich closed-forest patches. Second, the recent global
increase in atmospheric CO2 may be changing the competitive balance between savanna and forest by enabling C3 trees to grow fast enough to escape the fire trap presented by flammable C4 grasses. 相似文献